Dissertation Krugmann

Schriftenreihe des Instituts für Tierzucht und Tierhaltung der

Christian-Albrechts-Universität zu Kiel, Heft 228, 2019

©2019 Selbstverlag des Instituts für Tierzucht und Tierhaltung

der Christian-Albrechts-Universität zu Kiel

Olshausenstraße 40, 24098 Kiel

Schriftleitung: Prof. Dr. J. Krieter

ISSN: 0720-4272

Gedruckt mit Genehmigung des Dekans der Agrar- und Ernährungswissen-

schaftlichen Fakultät der Christian-Albrechts-Universität zu Kiel

Aus dem Institut für Tierzucht und Tierhaltung

der Agrar- und Ernährungswissenschaftlichen Fakultät


Assessment of growing pigs‘ positive affective state using

behavioural parameters and structural equation modelling

Dissertation

zur Erlangung des Doktorgrades

der Agrar- und Ernährungswissenschaftlichen Fakultät


vorgelegt von

M.Sc. Katja Lisabeth Krugmann

aus Lübeck

Kiel, 2019

Dekan: Prof. Dr. Dr. C. Henning

1. Berichterstatter: Prof. Dr. Joachim Krieter

2. Berichterstatter: Prof. Dr. Nicole Kemper

Tag der mündlichen Prüfung: 15. Mai 2019

Die Förderung erfolgte dankenswerter Weise aus Mitteln des Bundesministeriums für Ernährung und Landwirtschaft (BMEL) aufgrund eines Beschlusses des Deutschen

Bundestages und der H. WILHELM SCHAUMANN STIFTUNG.

Meiner Familie

TABLE OF CONTENTS

GENERAL INTRODUCTION ........................................................................................ 11

CHAPTER ONE Are behavioural tests capable of measuring positive affective states in growing pigs? .......... 17

CHAPTER TWO Playing behaviour – a suitable indicator to measure positive emotions in growing pigs? ..... 39

CHAPTER THREE Can tail and ear postures be suitable to capture the affective state of growing pigs? ............ 63

CHAPTER FOUR Investigation of influence of growing pigs’ positive affective state on behavioural and

physiological parameters using structural equation modelling ............................................... 85

GENERAL DISCUSSION ..................................................................................................... 111

GENERAL SUMMARY ........................................................................................................ 125

ZUSAMMENFASSUNG ....................................................................................................... 129

ATTACHMENT .................................................................................................................... 133

11

GENERAL INTRODUCTION

In the last few decades, there has been increasing concern about livestock’s husbandry and

animal welfare issues (SandØe & Simonsen, 1992). Animal welfare represents a

multidimensional complex about which there are different opinions. One well-known

definition of animal welfare includes three general components: 1) basic health and biologic

functioning, which include animals’ freedom from disease and suffering and their

fundamental capability to perform, 2) natural living, in accordance with given opportunities to

practice natural behaviour in their housing systems and 3) the animals’ affective state,

especially regarding the share of their experienced positive and negative emotions (Fraser,

2008). As all three components are equally important, good welfare is only achieved if all

components are satisfied. Whereas extensive research in the area of the basic health and

functioning and natural living has already been carried out (Blokhuis, 2013), the animals’

affective state still constitutes a latent variable which is not itself measurable and must be

evaluated indirectly by different parameters. According to Fraser (2008), the animals’

affective state consists of different emotions such as pleasure, happiness, pain and suffering

and other feelings such as hunger and thirst that are experienced as pleasant or unpleasant.

Additionally, the primarily positive affective state presumably includes experienced, pleasant

emotions such as happiness (Ortony and Turner, 1990; Diener and Lucas, 2000) whereas

unpleasant emotions such as fear, pain or suffering probably indicate the animals’ more

negative affective state. In principle, emotions are described as intense, short-lived affective

responses to a stimuli related to specific body changes (Dantzer, 1988). More classically, they

are characterised as containing a behavioural component (a posture or an activity), an

autonomic component (visceral and endocrine responses) and a subjective component

(emotional experience or feeling) (Dantzer, 1988). Further, it is stated that emotional

properties do exist in animals since emotional reactivity has been identified as consistent

across time and situation (Boissy, 1998; Erhard and Schouten, 2001).

For the assessment of animals’ negative affective states, stress-related parameters such as e.g.

salivary cortisol concentrations are examined, while reliable measurement methods for the

animals’ positive affective state are lacking (Marcet Rius et al., 2018). Up to now, assessment

systems such as the “Welfare Quality®” protocol have been partially unreliable and strongly

influenced by subjective perceptions, especially in terms of the “Qualitative Behaviour

12

Assessment” (Czycholl et al., 2017; Temple et al., 2011; Bokkers et al., 2012; Tuyttens et al.,

2014). Thus, an objective measurement of the primarily positive affective state still remains

considerably difficult and an enormous challenge (Duncan, 2005). Hence, scientific

investigation of positive emotions has long been omitted (Boissy et al., 2007), but has

continued to gain significance in the course of current livestock sciences.

In previous studies, animals in cognitive bias tests have responded differently according to

their affective state (Harding et al., 2004; Scollo et al., 2014). Correspondingly, animals in a

more negative affective state, due to anxiety, depression or a barren environment, react with a

more pessimistic behavioural response to stimuli. Thus, it seems conceivable that behavioural

parameters such as the animals’ way of reacting to stimuli in standardised tests such as the

human-approach or novel-object test, playing behaviour or body language signals could be

suitable to draw conclusions concerning the primarily positive affective state. For instance,

playing behaviour in livestock is stated as “luxury” behaviour (Lawrence, 1987), which only

occurs when the animals’ primary needs reach a satisfactory level and optimal environmental

conditions prevail (Lawrence, 1987; Held and Špinka, 2011). Further, in human depression

research, physiological changes in hippocampal structures, adrenal glands (Czéh et al., 2006)

and salivary immunoglobulin-A contents (Bosch et al., 2004) and protein compositions

(Grigoriev et al., 2003) have proven to be indicative of more or fewer positive affective states,

which could possibly be verified in animals as well.

Aim of the present thesis

The aim of this thesis was to obtain a better understanding of livestock’s particularly positive

affective state, exemplified by investigations with fattening pigs. In the course of this,

potential indicators were to be derived which enabled feasible and reliable measurement of

the pigs’ particularly positive affective state. Various behavioural and physiological

parameters were selected from previous literature studies. All parameters were examined for

their suitability as potential indicators to assess the fattening pigs’ primarily positive affective

state in two different housing systems on three different farms.

The first Chapter investigates whether behavioural tests such as the human approach (HAT)

or novel object test (NOT), which are considered as suitable tests for assessing the level of

fear or anxiety in animals, are suitable to detect fattening pigs’ positive affective state. Each

pig was subjected three times to the HAT and NOT during fattening whereby the first, second

13

and third points of testing were at the beginning, middle and end of fattening, respectively. At

each point of testing, the pigs were tested alone in their home pen and three behavioural

variables were noticed and subsequently analysed: the approach latency (AL), duration of

contacts (DC) and number of contacts (NC).

The second Chapter compares the occurrence of the fattening pig’s playing behaviour in the

two different housing systems regarding the total duration of playing behaviour (s/h),

locomotor play (s/h) and social play (s/h) and whether these could be useful to assess the pig’s

particularly positive affective state. The playing behaviour was recorded for two days at the

beginning and two days at the end of fattening.

The third Chapter deals with body language signals of the examined fattening pigs, such as

their curled-up tails or forward-directed ears and proved their suitability to enable detection of

the pigs’ primarily positive affective state. The body language signals were analysed for four

days in total, two days at the beginning and two days at the end of fattening, respectively.

The fourth Chapter provides insights into the relationships between a large variety of

behavioural parameters such as behavioural tests, playing behaviour or body language signals

and physiological parameters such as hippocampal structures and salivary immunoglobulin-A

content respectively protein compositions which were collected during the related research

project. The partial least squares structural equation modelling method was applied to analyse

the most appropriate parameters to estimate the latent variable of the fattening pigs’ primarily

positive affective state and to evaluate the latent structures in between the behavioural and

physiological parameters.

14

REFERENCES

Blokhuis, H., Veissier, I., Jones, B., Miele, M., 2013. Improving farm animal welfare –

Science and society working together: the Welfare Quality approach. In: Blokhuis, H.,

Miele, M., Veissier, I., Jones, B. (Eds.), Improving farm animal welfare. Wageningen

Academic Publishers, Wageningen, Gelderland, Netherlands.

Boissy A., 1998. Fear and fearfulness in determining behavior. In: Grandin T, editor. Genetics

and the behavior of domestic animals. New York: Academic Press; 67–111.

Boissy, A., Manteuffel, G., Jensen, Bak, M., Randi Oppermann, M., Spruijt, B., Keeling, L.

J., 2007. Assessment of positive emotions in animals to improve their welfare. In:

Physiology & behavior 92 (3), 375–397.

Bokkers, E.A.M., de Vries, M., Antonissen, I., de Boer, I.J.M., 2012. Inter- and intra-observer

reliability of experienced and inexperienced observers for the Qualitative Behaviour

Assessment in dairy cattle. Animal Welfare 21, 307-318.

Bosch, J.A., Ring, C., Amerongen, A.V.N., 2004. Academic examinations and immunity:

academic stress or examination stress? Psychosomatic Medicine, 625–627.

Czéh, B., Simon, M., Schmelting, B., Hiemke, C., Fuchs, E., 2006. Astroglial Plasticity in the

hippocampus is affected by psychological stress and concomitant fluoxetine treatment.

Neuropsychopharmacology, 1616–1626.

Czycholl, I., Kniese, C., Schrader, L., Krieter, J., 2017. Assessment of the multi-criteria

evaluation system of the Welfare Quality® protocol for growing pigs. animal 11,

1573–1580.

Dantzer R., 1988. Les émotions. Paris: Presses Universitaires de France; 121.

Diener, E., Lucas, R.E., 2000. Subjective emotional well-being. In M. Lewis and J.M.

Haviland-Jones (Eds.), Handbook of emotions (2nd ed., pp. 325-337). New York:

Guilford Press.

Duncan, I.J.H., 2005. Science-based assessment of animal welfare: farm animals. Revue

Scientifique et Technique – Office International de Epizooties 24(2):483-492.

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Erhard H.W., Schouten W.G.P., 2001. Individual differences and personality. In: Keeling LJ,

Gonyou HW, editors. Social behavior in farm animals. Wallingford: CAB

International; 333–52.

Fraser, D., 2008. Understanding animal welfare. Acta Veterinaria Scandinavica.

Grigoriev, I.V., Nikolaeva, L.V., Artamanov, I.D., 2003. Protein Content of Human Saliva in

Various Psycho-emotional States. Biochemistry, 405–406.

Harding, E.J., Paul, E.S., Mendl, M., 2004. Animal behaviour: cognitive bias and affective

state. Nature 427, 312.

Held, S.D.E., Špinka, M., 2011. Animal Play and animal welfare. Animal Behaviour 81, 891-

899.

Lawrence, A., 1987. Consumer demand theory and the assessment of animal welfare. Animal

Behaviour 35, S. 293-295.

Marcet Rius, M., Cozzi, A., Bienboire-Frosini, C., Teruel, E., Chabaud, C., Monneret, P.,

2018. Selection of putative indicators of positive emotions triggered by object and

social play in mini-pigs. Applied Animal Behaviour Science 202, 13–19.

Ortony, A., Turner, T.J., 1990. What’s basic about basic emotions? Psychological Review, 97,

315-331.

SandØe, P., Simonsen, H.B., 1992. Assessing animal welfare: where does science end and

philosophy begin? Animal Welfare 1, 257-267.

Scollo, A., Gottardo, F., Contiero, B., Edwards, S.A., 2014. Does stocking density modify

affective state in pigs as assessed by cognitive bias, behavioural and physiological

parameters? Applied Animal Behaviour Science 153, 26–35.

Temple, D., Dalmau, A., Ruiz de la Torre, J., Manteca, X., Velarde, A., 2011. Application of

the Welfare Quality protocol to assess growing pigs kept under intensive conditions in

Spain. Journal of Veterinary Behavior 6:138–149.

Tuyttens, F.A.M., de Graaf, S., Heerkens, J.L.T., Jacobs, L., Nalon, E., Ott, S., Stadig, L.,

Van Laer, E., Ampe, B., 2014. Observer bias in animal behaviour research: can we

believe what we score, if we score what we believe? Animal Behaviour 90, 273-280.

17

CHAPTER ONE

Are behavioural tests capable of measuring positive affective states in

growing pigs?

K.L. Krugmann , F.J. Warnken, J. Krieter, I. Czycholl

Institute of Animal Breeding and Husbandry, Christian-Albrechts-University Kiel,

Olshausenstr. 40, D-24098 Kiel, Germany.

Submitted to Applied Animal Behaviour Science

18

ABSTRACT

This study examined whether behavioural tests such as the human approach (HAT) or novel

object test (NOT), which are considered as suitable tests for assessing the level of fear or

anxiety in animals, are suitable to detect a positive affective state in 297 fattening pigs from

three different farms. The investigated farms consisted of a barren (farm 1, n=160) and an

enriched (farm 2, n=106; farm 3, n=31) housing system that varied in terms of availability of

space, enrichment and seasonal influences. Each pig was subjected three times to the HAT

and NOT during fattening whereby the first, second and third points of testing were at the

start, middle and end of fattening, respectively. Measuring the time (in seconds) which the

pigs needed to come into physical contact with the human or novel object resulted in three

behavioural variables: the approach latency (AL), duration of contacts (DC) and number of

contacts (NC). The pigs housed in the barren environment showed quicker AL than the

enriched-housed pigs (HAT: farm 1: 11.3 ± 1.1s vs. farm 2: 65.4 ± 1.1s respectively farm 3:

56.2 ± 1.3s (in the middle of fattening); HAT: farm 1: 7.4 ± 1.1s vs. farm 2: 57.1 ± 1.1s

respectively farm 3: 58.3 ± 1.3s (at the end of fattening); NOT: farm 1: 6.4 ± 1.1s vs. farm 2:

21.7 ± 1.1s respectively farm 3: 10.9 ± 1.2s (in the middle of fattening); NOT: farm 1: 4.5 ±

1.1s vs. farm 2: 23.0 ± 1.1s respectively farm 3: 9.0 ± 1.2s (at the end of fattening)). The same

pattern of behaviour was observed for the DC in the HAT but not in the NOT (HAT: farm 1:

48.6 ± 1.1s vs. farm 2: 4.8 ± 1.1s respectively farm 3: 4.0 ± 1.3s (in the middle of fattening);

HAT: farm 1: 83.8 ± 1.1s vs. farm 2: 6.3 ± 1.1s respectively farm 3: 7.6 ± 1.3s (at the end of

fattening)). Due to controversially discussed literature, it is difficult to conclude whether the

described definite differences of the pigs’ behaviour between the two housing systems might

indicate useful behavioural indicators to detect a positive affective state. Nevertheless, the

results of this study lay relevant foundations for further investigations concerning the

assessment of the positive affective state of fattening pigs. In addition, this study increases

knowledge regarding the validity of the HAT and NOT in general.

Keywords: animal welfare; human approach test; novel object test; pigs; positive emotions

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INTRODUCTION

Certain behavioural reactions of animals are commonly measured by behavioural tests

performed in standardized environments and seem to capture some parts of the behavioural

tendencies of the individual animal (Forkman et al., 2007). Thus, implementations of

behavioural tests are also used in breeding decisions (Wilsson and Sundgren, 1997).

Additionally, a large number of behavioural tests focus on assessing emotions (Carreras et al.,

2017) whereas the HAT and NOT are known to be suitable to measure the level of fear or

anxiety in animals (e.g. Murphy et al., 2014; Hemsworth and Coleman, 1998). Moreover, they

are used to evaluate the effectiveness of medical treatments such as anxiolytics (Dalmau et al.,

2009). Hence, the reactions to sudden or unfamiliar events are used to assess the animals’

fearfulness (Boissy, 1995) whereby the amount of avoidance or approach behaviour is

suggested to provide a measure of the level of fear in animals (Hemsworth and Coleman,

1998). Accordingly, a shorter latency to approach novel stimuli is maintained to show less

fearful animals (Forkman et al., 2007) so that it could be imagined that these animals also

possess a more positive affective state since fear is detected as a strong negative emotion,

which is also often included in assessments of animal welfare (Forkman et al., 2007). The

affective state, which is determined as an essential part of animal welfare, constitutes the

experienced positive and negative emotions of animals (Fraser, 2009). However, it still poses

an enormous challenge to measure the affective state of animals objectively as previous

assessment systems are partially unreliable and strongly influenced by subjective perceptions

(Czycholl et al., 2017; Temple et al., 2011; Bokkers et al., 2012; Tuyttens et al., 2014). The

generally criticized intensive housing conditions of farm animals and a greater demand for

more “animal friendly” systems, the necessity to detect reliable and suitable indicators that

identify animals’ especially positive affective state (Marcet Rius et al., 2018) have continued

to gain significance in the course of the increasing interest in animal welfare.

It is conceivable that behavioural features such as the latency to approach and contact novel

stimuli, which represents the usual measure to assess fear (Carreras et al., 2017) and other

measures, such as the duration or number of contacts provide valuable information on

behavioural patterns of animals. Aside from the measuring of the level of fear, the

behavioural variables mentioned reflect the willingness to explore novel objects, and the

boldness of the animals’ personality can also be measured through responses to novel objects,

threatening stimuli or environments (Carter et al., 2012). Furthermore, van der Staay et al.

20

(2017) suggest that the affective state of animals is influenced by environmental conditions.

Moreover, primarily the NOT appears to be sensitive to marginal changes in the environment

(Bracke and Spoolder, 2008). Hence, it could be imaginable that animals which are housed in

differing environments, e.g. in terms of barren or enriched habitats, different handling

treatments or further stimuli, react in different ways to sudden or unfamiliar events as are said

to be measured in behavioural tests (Boissy, 1995). Possibly, these expected, different

behavioural reactions could be useful to obtain a better comprehension of the affective state of

farm animals.

Thus, the present study aimed at determining behavioural patterns of fattening pigs housed in

different habitats that could be measured in the HAT and the NOT to detect suitable

behavioural indicators to assess livestock’s affective state. Thereby it has been hypothesized

that particularly quicker AL and longer DC indicate less fearful and more curious pigs that

simultaneously might possess a more positive affective state.

MATERIALS AND METHODS

Animals and housing conditions

The behavioural data were collected on three farms with different housing systems in

Northern Germany between November 2016 and September 2017. 297 fattening pigs bred

from commercial crossbred dams (Large White x Landrace) and sired by Pietrain boars were

tested in total. The tails of the pigs were undocked, and the boars were castrated. The housing

systems differed primarily in terms of the space availability (m²/pig), an enriched or barren

habitat and the climatic conditions.

Farm 1 depicted a barren habitat for the pigs and was a fattening stable in which the pigs were

kept in groups of 19 to a pen. The pens measured 3.70 x 4.70m resulting in 0.92m² per pig.

The floor was half planed, and half perforated with no bedding. These pigs were fed ad

libitum with pelleted feed through a dry-feeding machine and water was accessible through

nipple drinkers. The ambient temperature was 18°C. There was daily artificial light for eight

hours (07:00-15:00).

An ecological fattening stable with an enriched habitat, such as inside and outside pens (in

total 4.90 x 9.80m) with straw bedding represented Farm 2. There was a roofed (2.70 x

21

4.90m) and roofless area (3.50 x 4,90m) in the outside pens. At the beginning of fattening 54

pigs were housed in one pen with a total area of 48.02m² (4.90 x 9.80m) resulting in 0.89m²

per pig. Throughout fattening the animals were divided into three of these pens evenly so that

each pig attained an availability of space of 2.67m². These pigs were fed ad libitum with

mealy feed.

Farm 3 constituted an ecological fattening stable with a specifically enriched habitat for the

pigs. There were straw-bedded inside pens and roofed straw-bedded outside pens as well as

outside pens with soiled floor for rooting. The dimension of these pens measured in total

83.32m² (8.33m² per pig with a usual occupancy of 10 pigs per pen). The feeding was ad

libitum with liquid feed.

On Farm 2 and Farm 3 there were also nipple drinkers and hayracks available and the daylight

length as well as the ambient temperature was determined by the season. Once a day these

pigs got bread and different fruits and vegetables.

Experimental procedure

297 fattening pigs of three different farms were subjected to three HATs and three NOTs

during their fattening. The first, second and third points of testing were conducted at the

beginning, middle and end of fattening. Each pig was tested alone in the home pen. Both

behavioural tests were performed with a one-day time lag in between and never on the same

day. The pigs were given an acclimation period of two minutes followed by a test period of

three minutes that started when the unknown human entered, or the novel object were brought

into the test area. The unknown human in the HAT was always a female person who the pigs

did not know from daily routine work. She wore a clean overall plus rubber boots and stood

motionless in the middle of the pen during the entire test phase. A plastic duck presented to

the pigs in three different sizes (according to the age and the live weight of the animals)

represented the utilized novel objects in the NOT. These ducks showed a yellow body colour

with a red coloured beak. With the help of a rod and a string, they were held in the middle of

the pen at the height of the pig's head. Always the same observing person noted the analysed

variables during the test phase: the approach latency (AL), the duration of contacts (DC) and

the number of contacts (NC). AL represented the time in seconds that each pig needed to

approach the unknown human or the novel object until the snout touched the human or the

novel object. DC exposed the accumulated seconds in which the pigs touched the human or

22

the novel object with their snouts. The entire number of snout contacts that occurred during

the test phase was indicated by NC. Further, an AL of 180 seconds was noted if the pigs did

not come into contact with the human or the novel object.

The behavioural tests were conducted in the home pens of the respective housing systems. On

Farm 1 the home pen (3.70 x 4.70m) was used completely. Parts of the outdoor area were

used for testing the pigs on the other two farms. The amount of space for testing on Farm 2

measured 6.20 x 4.90m with a roofed and unroofed area. On Farm 3, the roofed outdoor area

was utilized (2.40 x 3.80m).

Statistical analysis

Statistical analyses were performed with SAS® 9.4 (SAS Institute Inc., 2017). The

behavioural data were not normally distributed. Thus, all data were log10 (X + 1) transformed

to obtain normality of residuals of the used linear mixed model (PROC MIXED). Fixed

effects were added to the model in a stepwise manner. The Akaike’s information criteria

corrected (AICC) and the Bayesian information criteria (BIC) were used to compare the

different models. The model with the smallest AICC and BIC values was chosen and included

the fixed effects farm (1-3), batch (1, 2) nested in farm, points of testing (beginning, middle

and end of fattening) nested in farm and gender (female, male) together with a random effect

of each individual pig nested in farm, batch and gender. The significance of differences in the

least square means was adjusted with the Bonferroni-correction. Statistical significance was

determined at p<0.05.

The residuals of the linear mixed models of all behavioural variables of both behavioural tests

were correlated through the Pearson correlation coefficient (PROC CORR).

23

RESULTS

Human Approach Test (HAT)

Approach latency (AL) HAT

Differences between the farms at each point of testing

No significant differences between the AL were observed on farm 1 and farm 2 at the

beginning of fattening (Figure 1). On farm 1, the AL was significantly lower than on farm 2 at

the middle and the ending of the fattening (Figure 1). There were no significant differences

between the AL of farm 1 and farm 3 at the beginning of the fattening and significantly lower

AL on farm 1 than on farm 3 at the middle and the ending of the fattening (Figure 1). No

significant differences between the AL were observed on farm 2 and farm 3 at the beginning,

middle and ending of the fattening (Figure 1).

Differences between the points of testing within each farm

The AL significantly decreased throughout fattening from the beginning to end on farm 1 and

farm 2 (Figure 1). On farm 3, no significant differences in the AL were observed between the

beginning and end of fattening (Figure 1).

Duration of contact (DC) HAT


At the beginning, middle and end of fattening the pigs on farm 1 showed longer DC than the

pigs on farm 2 (Figure 2). There were no significant differences observed between the DC of

farm 1 and farm 3 at the beginning of fattening (Figure 2). At the middle and end of fattening,

the pigs on farm 1 showed longer DC than the pigs on farm 3 (Figure 2). On farm 2, the DC

were significantly lower than on farm 3 at the beginning of fattening and there were no

significant differences between the DC on farm 2 and farm 3 at the middle and end of

fattening (Figure 2).


On farm 1 and farm 2, the DC significantly increased from the beginning to the end of

fattening (Figure 2). On farm 3, there was no significant increase or decrease of the DC

between the beginning and end of fattening observed (Figure 2).

24

Figure 1: LS-means and standard errors (s) (retransformed) of the approach latency in the HAT at each point of testing; a, b, c different letters indicate significant differences within the farm between the different points of testing (p<0.05); A, B, C different letters indicate significant differences between the farms within the different points of testing (p<0.05).

25

Figure 2: LS-means and standard errors (s) (retransformed) of the duration of contacts in the HAT at each point of testing; a, b, c different letters indicate significant differences within the farm between the different points of testing (p<0.05); A, B, C different letters indicate significant differences between the farms within the different points of testing (p<0.05).

Number of contacts (NC) HAT


At the beginning and middle of fattening the pigs on farm 1 showed significantly higher NC

than the pigs on farm 2 (beginning of the fattening: farm 1: 1.8 ± 1.0s vs. farm 2 1.3 ± 1.0s;

p<0.05; middle of the fattening: farm 1: 2.9 ± 1.0s vs. farm 2: 1.8 ± 1.0s; p<0.05). At the end

of fattening there were no significant differences between the NC of farm 1 and farm 2 (farm

1: 2.3 ± 1.0s vs. farm 2: 1.9 ± 1.0s; p>0.05). There were no significant differences observed

between the NC of farm 1 and farm 3 at the beginning and end of fattening (beginning of

fattening: farm 1: 1.8 ± 1.0s vs. farm 3: 1.7 ± 1.1s; p>0.05; end of fattening: farm 1: 2.3 ± 1.0s

vs. farm 3: 1.8 ± 1.1s; p>0.05). At the middle of fattening, the pigs on farm 1 showed

significantly higher NC than the pigs on farm 3 (farm 1: 2.9 ± 1.0s vs. farm 3: 1.5 ± 1.1s;

p<0.05). On farm 2, there was significant lower NC than on farm 3 at the beginning of

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fattening (farm 2: 1.3 ± 1.0s vs. farm 3 1.7 ± 1.1s; p<0.05) and at the middle and end of

fattening there were no significant differences between the NC of farm 2 and farm 3 (middle

of fattening: farm 2: 1.8 ± 1.0s vs. farm 3 1.5 ± 1.1s; p>0.05); end of fattening: farm 2: 1.9 ±

1.0s vs. farm 3: 1.8 ± 1.1s; p>0.05).


There was a significant increase in NC on farm 1 and farm 2 from the beginning to the end of

fattening (farm 1: 1.8 ± 1.0s vs. 2.3 ± 1.0s; p<0.05); farm 2: 1.3 ± 1.0s vs. 1.9 ± 1.0s; p<0.05)

and no significant differences between the NC of the beginning and end of fattening on farm 3

(1.7 ± 1.1s vs. 1.8 ± 1.1s; p>0.05).

Gender HAT

The female pigs showed significantly lower AL and longer DC than the castrated males

(Table 1). No significant differences were observed between the NC of the female and

castrated male pigs (Table 1).

Table 1: LS-means and standard errors (s) (retransformed) of the behavioural variables in the HAT and NOT of different gender

Behavioural

variables

Female Male p-value

HAT-AL 33.36 ± 1.09a 52.05 ± 1.11b 0.04

HAT-DC 10.97 ± 1.10a 7.75 ± 1.12b 0.005

HAT-NC 1.96 ± 1.03a 1.82 ± 1.03a 0.05

NOT-AL 12.52 ± 1.08a 16.14 ± 1.09b 0.01

NOT-DC 25.98 ± 1.08a 20.95 ± 1.10b 0.03

NOT-NC 3.23 ± 1.03a 3.04 ± 1.03a 0.1

HAT = human approach test; NOT = novel object test; AL = approach latency; DC = duration of contact; NC = number of contacts; a, b different letters indicate significant differences between the gender (p<0.05).

27

Novel Object Test (NOT)

Approach latency (AL) NOT


At the beginning, middle and end of fattening significantly lower AL were observed on farm

1 than on farm 2 (Figure 3). At the beginning and middle of fattening there were no

significant differences between the AL on farm 1 and farm 3. At the end of fattening the pigs

on farm 1 showed lower AL than the pigs on farm 3 (Figure 3). There were no significant

differences between the AL on farm 2 and farm 3 at the beginning, middle and end of

fattening (Figure 3).


The AL on farm 1 and farm 2 decreased from the beginning to the end of fattening (Figure 3).

No significant differences of the AL were observed at the beginning and end of fattening on

farm 3 (Figure 3).

Duration of contact (DC) NOT


There were longer DC on farm 1 than on farm 2 at the beginning and end of fattening and no

significant differences between the DC of farm 1 and farm 2 at the middle of fattening (Figure

4). On farm 1 and farm 3 there were no significant differences observed between the DC at

the beginning, middle and end of fattening (Figure 4). At the beginning of fattening the pigs

on farm 2 showed shorter DC than the pigs on farm 3 and there were no significant

differences between the DC of farm 2 and farm 3 at the middle and end of fattening (Figure

4).


The pigs on farm 1 and farm 2 showed a significant increase in DC from the beginning to the

end of fattening and there were no significant differences between the DC of the beginning

and end of fattening on farm 3 (Figure 4).

28

Figure 3: LS-means and standard errors (s) (retransformed) of the approach latency in the NOT at each point of testing; a, b, c different letters indicate significant differences within the farm between the different points of testing (p<0.05); A, B, C different letters indicate significant differences between the farms within the different points of testing (p<0.05).

29

Figure 4: LS-means and standard errors (s) (retransformed) of the duration of contacts in the NOT at each point of testing; a, b, c different letters indicate significant differences within the farm between the different points of testing (p<0.05); A, B, C different letters indicate significant differences between the farms within the different points of testing (p<0.05).

Number of contacts (NC) NOT


At the beginning, middle and end of fattening the pigs on farm 1 showed significantly higher

NC than the pigs on farm 2 (beginning of fattening: farm 1: 3.3 ± 1.0s vs. farm 2 1.9 ± 1.0s;

p<0.05; middle of fattening: farm 1: 3.6 ± 1.0s vs. farm 2: 2.8 ± 1.0s; p<0.05; end of

fattening: farm 1: 4.3 ± 1.0s vs. farm 2: 2.5 ± 1.0s; p<0.05). At the beginning, middle and end

of fattening there were no significant differences between the NC of farm 1 and farm 3

(beginning of fattening: farm 1: 3.3 ± 1.0s vs. farm 3 3.6 ± 1.1s; p<0.05; middle of fattening:

farm 1: 3.6 ± 1.0s vs. farm 3: 3.5 ± 1.1s; p<0.05; end of fattening: farm 1: 4.3 ± 1.0s vs. farm

3: 3.1 ± 1.1s; p<0.05). There was a significantly lower NC on farm 2 than on farm 3 at the

beginning of fattening (farm 2: 1.9 ± 1.0s vs. farm 3: 3.6 ± 1.1s; p<0.05) and no significant

differences between the NC of farm 2 and farm 3 at the middle and end of fattening (middle

30

of fattening: farm 2: 2.8 ± 1.0s vs. farm 3: 3.5 ± 1.1s; p>0.05; end of fattening: farm 2: 2.5 ±

1.0s vs. farm 3: 3.1 ± 1.1s; p>0.05).


On farm 1 and farm 2, there was a significant increase in NC from the beginning to the end of

fattening (farm 1: 3.3 ± 1.0s vs. 4.3 ± 1.0s; p<0.05; farm 2: 1.9 ± 1.0s vs. 2.5 ± 1.0s; p<0.05).

No significant differences were observed between the NC of the beginning and end of

fattening on farm 3 (3.6 ± 1.1s vs. 3.1 ± 1.1s; p>0.05).

Gender NOT

The female pigs showed significant lower AL and higher DC than the castrated male pigs

(Table 1). There were no significant differences observed between the NC of the female and

castrated male pigs (Table 1).

Relationship between the behavioural variables

In the HAT, the AL was negatively correlated with the NC and DC (rp = -0.62 p<0.001; rp = -

0.68 p<0.001) whereas the NC was positively correlated with the DC (rp = 0.76 p<0.001)

(Table 2).

In the NOT, there was a positive correlation observed between the NC and DC (rp = 0.74

p<0.001) and there were negative correlations between the AL and the NC respectively DC

(rp = -0.55 p<0.001 respectively rp = -0.61 p<0.001) (Table 2).

The DC of the NOT was positively correlated with the NC respectively DC of the HAT (rp =

0.21 p<0.001 respectively rp = 0.24 p<0.001) (Table 2).

31

Table 2: Pearson rank correlations between the residuals of the linear mixed models of the behavioural variables

Behavioural

variables HAT-DC HAT-AL NOT-NC NOT-DC NOT-AL

HAT-NC 0.76 -0.62 0.16 0.21 -0.16

HAT-DC -0.68 0.16 0.24 -0.19

HAT-AL -0.13 -0.18 0.18

NOT-NC 0.74 -0.55

NOT-DC -0.61

NOT-AL

Correlation coefficients in bold indicate moderate respectively high and statistically significant correlations (p<0.05).

DISCUSSION

The present study aimed to examine whether behavioural tests like the HAT or NOT

performed with fattening pigs of two different housing systems are useful to assess their

positive affective state.

In the following, the behavioural variables AL, DC and NC are discussed together for both

behavioural tests. The AL indicated definite differences in the pigs’ behaviour between the

two different housing systems in both the HAT and NOT especially at the middle and end of

fattening. The pigs housed in the barren environment showed lower AL than the enriched-

housed pigs. The same pattern of behaviour was observed for the DC in the HAT but not in

the NOT. Finally, the NC showed no definite differences of the pigs’ behaviour between the

two housing systems, neither in the HAT nor in the NOT.

Approach latency (AL)

According to Brown et al. (2009) quicker latencies to approach novel stimuli, such as

unknown humans or novel objects, are associated with less fearful animals. Therefore it could

be imaginable that these barren-housed pigs, which showed significantly quicker AL, possess

a more positive affective state due to less fearfulness but the quicker AL could also be a

reason for a stronger motivation to explore novel stimuli (Stolba and Wood-Gush, 1980)

32

related to boredom in the environment of these barren-housed pigs. Additionally,

Wemelsfelder et al. (2000) argued that enriched-housed pigs might be less fearful or more

curious to explore a novel object or a person in the home pen. But, simultaneously, barren-

housed pigs seemed to be more motivated to explore a novel object or a person in the home

pen probably due to fewer exploration possibilities in their habitat compared to enriched-

housed pigs. Further on, Forkman et al. (2007) claim that the avoidance reaction of the animal

appears to be essential as both a non-curious and a fearful animal will show long latencies to

approach. Consequently, it is difficult to determine, whether the quicker AL of the barren-

housed pigs might represent behavioural indicators for a more positive affective state possibly

because of less fearfulness, because other authors maintain that barren environments have

negative effects on pig welfare (Beattie et al., 1995). Thus, it could be also conceivable that

these quicker AL of the pigs housed in the barren habitat describe their more negative

affective state, possibly due to boredom and fewer exploration opportunities in their

environment.

The decreasing AL from the first to the third points of testing during fattening on farm 1 and

farm 2 both in the HAT and NOT could be related to a gradual reduction in fear;

Wemelsfelder et al. (2000) also observed a decreasing latency to enter the test arena for all

pigs while the experiment progressed. Additionally, Forkman et al. (2007) suggest that fear

and anxiety decrease with age, which could also explain the decreasing AL during fattening

on farm 1 and farm 2. The reduced level of fear and anxiety probably also causes the pigs to

get used to unknown humans or novel objects (Forkman et al., 2007) so that AL decreases

when the fattening progresses.

Moreover, an intensive monitoring of the avoidance reaction of the pigs e.g. regarding a high

latency to approach the unknown human or the novel object might be able to evaluate whether

the pigs show avoidance reactions or do not approach the novel stimuli due to lack of interest

(possibly related to various exploration opportunities in the environment) or fear and anxiety

accompanied by flight behaviour. The implementation of a forced human approach test might

be a possible solution to detect the reason of the avoidance reaction of the pigs whereby

animals which flee when humans approach them are known to be fearful (Pedersen et al.,

2003). Also Waiblinger et al. (2006) suggest that forced and voluntary approach tests measure

the animals’ behaviour in differing ways: the forced approach test might increase the

likelihood that an animal responds more actively to the human whereas in the voluntary

33

approach test the chances of getting no response or a passive response might probably be

higher. Hence, related observations between high approach latencies and the avoidance

reaction could provide more detailed information about a more positive, respectively more

negative affective state of the examined pigs.

Duration of contacts (DC)

In the HAT, there was a longer DC observed in the barren housing system (farm 1) than in the

enriched housing system (farm 2 and farm 3) at the middle and end of fattening. This definite

difference between the DC of the pigs in the two different housing systems could also be

related to the level of motivation to explore novel stimuli. Stolba and Woodgush (1981) argue

that the pigs’ interaction with a novel object decreased with increasing environmental

complexity and that the pigs in more intensive housing systems were more interested in the

novel object and that their interest maintained for a longer period. Consequently, this longer

DC related to a high level of motivation to explore novel stimuli in the barren-housed pigs

could imply a behavioural indicator of less welfare and therefore a less positive affective state

of these animals. Nevertheless, this definite difference in the pigs’ behaviour between the two

housing systems was only observed in the HAT. In the NOT, there were significant

differences of the pigs’ behaviour between the three farms, but not between the two housing

systems. Hence, this might imply that the HAT and NOT do not measure the same

behavioural attributes. Also Boivin et al. (1992) found no relationship between open-field

tests and handling tests, possibly indicating that they do not reflect the same animal

characteristic, which was also displayed in the weak correlations between the behavioural

variables of the HAT and NOT. For example, in contrast to the NOT, the pigs’ behaviour in

the HAT was influenced by their previous experiences with humans. There are studies which

demonstrate that negative handling leads to more avoidance responses (Carreras et al., 2017).

Increasing DC was observed on farm 1 and farm 2 from the first to the third points of testing

during the fattening both in the HAT and NOT. Regarding this, Forkman et al. (2007) posit

that human and object investigation increases with age, suggesting that fear and anxiety

decrease with age and that there could be an habituation process that reduces the fear

responses.

34

Number of contacts (NC)

At the second point of testing in the HAT and third point of testing in the NOT, higher NC

was observed in the barren housing system (farm 1) than in the enriched housing system (farm

2 and farm 3). Reimert et al. (2014) also observed barren-housed pigs more frequently present

near the person than enriched-housed pigs. This can also be justified by less fearful pigs

respectively a higher motivation for exploring novel stimuli but again it is not clear whether

this pattern of behaviour is related to a more positive or more negative affective state.

Besides, this definite difference in the pigs’ behaviour was only shown at one of the six points

of testing during fattening in the HAT respectively NOT.

The increased NC from the first to the third point of testing during fattening on farm 1 and

farm 2 in the HAT and NOT might also be related to a habituation process (Forkman et al.,

2007), which lowered the level of fear and thereby increased the NC of the pigs with the

unknown human or the novel object.

Gender

The female pigs showed quicker AL and longer DC than the male pigs in both, the HAT and

NOT. This might indicate that female pigs are less fearful than male pigs. Reimert et al.

(2014) observed gilts approaching and touching a person and a novel object faster than the

barrows suggesting the female animals were less fearful than the male ones. The gilts of this

study also had lower basal cortisol concentrations than barrows (Reimert et al., 2014), which

could explain the reaction of the female pigs as less fearful since high cortisol concentrations

depicted an indication of stress (Jarvis et al., 2006), and stress is known to be often connected

with fear (Forkman et al., 2007).

Further, especially the higher AL of the male pigs than the female pigs in the HAT can be

explained by their castration and its consequences, since in studies by Reimert et al. (2013)

the castrated male piglets also responded more fearfully to novel situations than female

piglets. Additionally, in this study, the male pigs had higher salivary cortisol concentrations

than the female pigs (Reimert et al., 2013), which could also indicate a stressed and fearful

affective state, as mentioned before. It is supposed that the absence of gonadal testosterone

makes the castrated pigs more fearful (Reimert et al., 2013) and that handling by a human

during castration and the connected pain afterwards makes the castrated male pigs more

fearful of humans (Prunier et al., 2006) so that they approach them not as quickly as the

35

female pigs. Further studies with uncastrated boars would be useful to support these

assumptions.

Additionally, the development of brains could influence the exploratory behaviour of animals;

Fleming and Dilger (2017) claim that, in general, the female brain of pigs develops faster than

the male ones possibly explaining the shorter AL and longer DC of the female pigs in both

behavioural tests due to better developed cognitive abilities.

CONCLUSION

The results of the present study showed that HAT and NOT performed with fattening pigs of

two different housing systems might be suitable to assess their level of anxiety and fear, but,

simultaneously, they also appeared to be capable of showing a stronger or lower motivation to

explore novel stimuli making it difficult to draw a clear conclusion as to whether a high or

low level of motivation to explore indicates more negative or more positive affective states.

Conclusively, in this study, neither the HAT nor the NOT depicted autonomous, reliable

indicators of positive affective states in growing pigs. However, the results of this study lay

essential foundations for further investigations concerning the assessment of the positive

affective state of fattening pigs. Furthermore, the findings of this study provide more detailed

information about certain reactions to unknown humans or novel objects of fattening pigs,

which are housed in different environments.

ACKNOWLEDGEMENTS

The project is supported by funds of the Federal Ministry of Food and Agriculture (BMEL)

based on a decision of the Parliament of the Federal Republic of Germany via the Federal

Office for Agriculture and Food (BLE) under the innovation support programme.

36

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39

CHAPTER TWO

Playing behaviour – a suitable indicator to measure positive emotions in

growing pigs?




Submitted to Journal of Animal Science

40

ABSTRACT

There is a lack of suitable measurement methods which are established for determining the

well-being of livestock. Thus, the aim of the present study was to examine whether the

occurrence of playing behaviour in fattening pigs (n=228) in different housing systems can be

used as an indicator to identify their positive affective state. The investigated housings

consisted of a barren (farm 1, n=138) and two enriched (farm 2, n=54; farm 3, n=36) habitats

that varied in terms of availability of space, enrichment and seasonal influences. The

behaviour of the pigs was recorded for two days at the beginning of fattening (first fattening

phase) and two days at the end of fattening (final fattening). In the first fattening phase, the

pigs in the barren habitat played significantly more than those in the enriched habitats (farm 1:

8.3 ± 1.1 s/h; p<0.05 vs. farm 2: 1.5 ± 1.0 s/h; farm 3: 3.3 ± 1.0 s/h). In the final fattening

phase, this pattern was reversed with pigs showing significantly more playing behaviour in

the enriched environment (farm 2: 2.2 ± 1.0 s/h; farm 3: 2.7 ± 1.0 s/h vs. farm 1: 1.2 ± 1.0 s/h;

p<0.05). The locomotor playing behaviour did not indicate definite differences between the

two housing systems in the first fattening phase, but significantly more locomotor play in the

enriched than barren housing system in the final fattening (final fattening: farm 1: 0.7 ± 1.0

s/h vs. farm 2: 1.6 ± 1.0 s/h; farm 3: 1.3 ± 1.0 s/h; p<0.05). Conversely, the pigs in the barren

habitat showed significantly more social playing behaviour than the pigs in the enriched

housing system in the first fattening phase and there were no definite differences between the

two housing systems in the final fattening (first fattening phase: farm 1: 6.6 ± 1.0 (s/h) vs.

farm 2: 1.2 ± 1.0 s/h; farm 3: 2.0 ± 1.0 s/h; p<0.05). Taken together, these observations

clearly show that the occurrence of playing behaviour in fattening pigs varies across fattening

phases and different housing systems. However, it remains questionable and difficult to

interpret whether playing behaviour as a solitary indicator is reliable to determine positive

affective states in fattening pigs.

Keywords: affective state, animal welfare, pigs, playing behaviour, positive emotions

INTRODUCTION

Modern livestock farming is currently intensively involved in public and political debate.

Consumers are concerned about the well-being of farm animals, housing conditions have been

41

criticised and an increased focus on animal welfare is required (Rushen, 2003; Veissier et al.,

2012; Alban et al. 2015). Consequently, current science includes the aim of researching the

objective detection of livestock’s well-being (Webster, 2005). It has already been defined that

animal welfare consists of three basic parts: basic health and functioning, natural living, and

affective state (Fraser, 2008). Whereas extensive research in the area of the basic health and

functioning and natural living has already been carried out (Blokhuis, 2013), there is a need to

detect the affective state of farm animals more intensively, which represents the pleasant or

unpleasant emotions they experience (Fraser, 2009). It has also been established that animals

are able to be aware to experience basic emotions such as happiness or anxiety (Panksepp,

1998). Up to now previous assessment systems like e.g. the “Welfare Quality®” protocol has

been partially unreliable and strongly influenced by subjective perceptions, especially in

terms of the “Qualitative Behaviour Assessment” (Czycholl et al., 2017; Temple et al., 2011).

Hence, the measurement of affective state is difficult and an enormous challenge (Duncan,

2005). Accordingly, it is further necessary to identify reliable and suitable indicators which

detect a livestock’s affective state and especially their positive emotions (Marcet Rius et al.,

2018).

Playing behaviour occurs in mammals, can be measured non-invasively and is easy to

recognise (Fraser and Duncan, 1998; Špinka et al., 2001; Barnard, 2004). It represents not

completely functional behaviour and does not contribute to the survival of animals

(Burghardt, 2005) as e.g. feed or water intake. Hence, playing behaviour includes apparent

main types of social (Vanderschuren et al., 1997), locomotor-rotational (Newberry et al.,

1988) and object play (Bateson and Young, 1981). Further, it has been stated that playing

only occurs when optimal environmental conditions prevail (Lawrence, 1987; Held and

Špinka, 2011) and the primary needs of animals (for food, safety, comfort, etc.) have reached

a satisfactory level (Buchenauer, 1981; Newberry, 1988). Authors have also suggested that

playing behaviour exists if the animals fare well and feel well (Siviy et al., 2006) especially in

terms of being free from sickness, injury, thermal stress or other challenges to their fitness and

health (Martin and Caro 1985; Burghardt, 2005). Moreover, it increases with improved

physical condition (Sharpe et al., 2002; Nunes et al., 2004; Cameron et al., 2008). Thus,

playing behaviour in livestock can be seen as “luxury” behaviour (Lawrence, 1987), which

decreases when animals experience negative emotions accompanied by e.g. threats to their

fitness (Fagen 1976; Martin and Caro 1985; Burghardt 2005) or adverse environmental

conditions (Müller-Schwartze et al., 1982; Siviy and Panksepp, 1985). Additionally, it has

42

been said to be often connected with animals experiencing positive emotions (Fraser and

Duncan, 1998; Špinka et al., 2001; Barnard, 2004; Burgdorf and Panksepp, 2006).

Furthermore, the playing behaviour of farm animals has been identified as a potential

indicator of current well-being (Fagen, 1976; Lawrence, 1987) and according to Boissy et al.

(2007), playing behaviour represents one of the most important indicators of positive

emotions in captive animals. Domestic pigs (Sus scrofa domesticus) are considered social,

intelligent mammals (D’Eath and Turner, 2009; Gieling et al., 2011) and research shows that

pig playing behaviour occurs beyond all playing behaviour categories: locomotor, social and

object (Donaldson et al., 2002; Newberry et al., 1988).

Along with the research aim of current scientific study this paper examined whether the

playing behaviour of fattening pigs in different housing systems can be used as an objective

measurement method to assess affective state. It has been hypothesised that the occurrence of

more playing behaviour in pigs might indicate their more positive affective state.


Animals and housing

The data were collected on three farms with different housing systems in Northern Germany

from November 2016 until September 2017. 228 fattening pigs bred from commercial cross-

bred dams (Large White x Landrace) and sired by Pietrain boars were used in total. All boars

were castrated and the tails were undocked. The housing systems differed especially in terms

of an enriched or barren habitat, the availability of space and climatic conditions. The pigs in

the barren housing system were weaned at the age of four weeks and those of the enriched

farms were weaned at six weeks.

Farm 1 depicted a conventional fattening stable (n=138) managed in a closed system in which

the pigs were housed in groups of 19 to a pen. These pens measured 3.70 x 4.70m resulting in

0.92m² per pig and the floor was half perforated and half concrete. Thus, farm 1 represents the

barren environment. The pigs were fed ad libitum with pelleted feed through a dry-feeding

machine involving an animal feeding space ratio of 1:4. Water was accessible through nipple

drinkers and the ambient temperature was 18° C. Metal chains, plastic pipes and balls were

43

offered as occupation material and in case of tail biting, the pigs were given gunny sacks.

Artificial light was provided for eight hours (07:00-15:00) per day.

Farm 2 (n=54) represented an ecological fattening stable with an enriched habitat, e.g. inside

and outside pens (in total 4.90 x 9.80m) with straw bedding. The outside pen included a

roofed (2.70 x 4.90m) and roofless area (3.50 x 4,90m). In the first fattening phase, there were

54 pigs housed in one pen with a total area of 48.02m² (4.90 x 9.80m) giving 0.89m² per pig.

After the first fattening phase, the animals were evenly divided into three of these pens so that

each pig had 2.67m² available space. The feeding was ad libitum with mealy feed by an

animal feeding space ratio of 1:4.

Also, the third farm (farm 3; n=36) constituted an ecological fattening stable with an enriched

environment. There were straw-bedded inside pens, roofed straw-bedded outside pens and

additionally special soil-based rooting areas. The whole pens measured 83.32m² in total

(8.33m² per pig with a usual occupancy of 10 animals per pen). The pigs were fed ad libitum

with liquid feeding including an animal feeding space ratio of 1:1.

On farms 2 and 3 there were also hay racks and nipple drinkers available but no occupation

material like metal chains, plastic pipes or balls as on farm 1. The ambient temperature as

well as the daylight length was determined by the season. Additionally, these pigs received

bread and different vegetables and fruits daily.

Experimental design

This study examined the playing behaviour of fattening pigs at the first fattening phase and at

the final fattening of two batches. The playing behaviour was determined by an ethogram

(Table 1) basing on previous research.

Recording and analysis of playing behaviour

The behaviour of the pigs was recorded for two days at the beginning and two days at the end

of the fattening using camera systems (HeiTel Digital Video GmbH, Kiel, Germany and

AXIS M30-VE Network Cameras). The cameras were positioned above the pens to obtain a

complete overview. Each of the pigs was marked individually with a sign on its back.

Continuous sampling was used to note the duration (s/h) of each playing behaviour sequence

(Table 1). Due to the great extent of the video data, it was assessed by four observers. These

observers were intensively trained using video test sequences at the beginning of the video

44

analysis and through repeated courses of instruction between the individual evaluation

sections. Additionally, the observers were applied cross-classified and not replaced during the

whole video analysis process. If several pigs played simultaneously, the sequence was

analysed for one pig and then rewound and analysed for the others. According to the testing

environment, the collected video material was examined following the different play

categories (Table 1) for eight hours per day for farm 1 and corresponding to the season for the

daylight hours for farms 2 and 3. Thus, the total duration of playing behaviour was divided by

the light day per hour in order to obtain a comparable attribute: the total duration of playing

behaviour (s/h). This procedure was also performed to obtain the total durations of playing

behaviour (s/h) for each play category (Table 1). The total duration of the locomotor play

(s/h) included all play categories that were shown exclusively by body movements whereas

the total duration of the social play (s/h) indicates all play categories with additional social

issues (Table 1).

Table 1: Ethogram of pigs’ playing behaviour

Play category Code Description References

Locomotor play Pivot a Gambolling or twirling the body by

1 to 360° Brown et al. (2015), Chaloupkova et al. (2007), Donaldson et al. (2002), Newberry et al. (1988)

Hop b Jumping off with the hind legs and angling the forelegs

Welker (1961)

Scamper c Energetic running (from 1m or along the whole pen)

Brown et al. (2015)

Flop d Dropping from an upright to a lying or sitting position on the pen floor

Brown et al. (2015), Chaloupkova et al. (2007), Donaldson et al. (2002)

Roll e Rolling lengthwise over the back Defined for this study Head-shaking j Moving the head back and forth

quickly with ears flapping Reimert et al. (2013)

Social play Non-harmful

fighting g Heads and mouths playfully

touching each other (no pushing anti-parallel/ without apparent aggression)

Brown et al. (2015)

Chase h Chasing other pigs playfully (without apparent aggression)

Welker (1961)

Invitation i Pushing the snout with minimal or moderate force into another pig’s body (if playing resulted afterwards)

Martin et al. (2015)

45


Statistical analyses were performed with SAS® 9.4 (SAS Institute Inc., 2017). The

behavioural data were not normally distributed. Thus, all data were log10 (X + 1) transformed

to obtain normality of residuals of the used linear mixed models (PROC MIXED). Fixed

effects were added to the model in a stepwise manner. The Akaike’s information criteria

corrected (AICC) and the Bayesian information criteria (BIC) were used to compare the

different models and the model with the smallest AICC and BIC values was chosen. The

model included the fixed effects observer (1-4), farm (farm 1, farm 2 and farm 3), gender

(female, male), points of testing (first fattening phase, final fattening) nested in farm, day (1,

2) nested in farm together with a random effect of each individual pig nested in farm and

gender and was used to analyse the data of the total duration of playing behaviour (s/h) and

total duration of locomotor respectively social play (s/h). The same model with the additional

fixed effect location nested in farm was utilised to compare the total duration of playing

behaviour (s/h) between the inside and outside area of farms 2 and 3. At this, a data-set was

used that contained only these two farms. Statistical significance was determined at p<0.05.

The significance of differences in the least square means was adjusted with the Bonferroni-

correction.

The differences between the farms within the individual play categories were analysed

descriptively using the Kruskal-Wallis test as there were too few observations in some play

categories to apply statistical models.

RESULTS

The following section represents first the results of each play category, i.e. how many pigs

performed which play category per farm. Then the retransformed LS-Means of the total

duration of playing behaviour (s/h) (all play categories summarised), of the locomotor play

(s/h) (all locomotor play categories summarised) and of the social play (s/h) (all social play

categories summarised) are presented.

Play categories

As illustrated in Figure 1, in the first fattening phase, the pigs on farm 1 performed no playing

behaviour in the categories “pivoting” (a), “hopping” (b) and “rolling” (e) whereas in the final

46

fattening these pigs showed no “rolling” (e) and no “chasing” (h) (Figure 1). Each play

category was observed during both phases on farm 2, except the play category “rolling” (e) in

the final fattening. On farm 3, each play category was observed during both phases.

Figure 1: Playing pigs (%) per farm within each play category. 1.=first fattening phase; 2.=final fattening; a=pivoting; b=hopping; c=scampering; d=flopping; e=rolling; g=non-harmful fighting; h=chasing; i=invitation play; j=head-shaking. a, b, c different letters indicate significant differences between the farms within the different points of testing (p<0.05)

Total duration of playing behaviour (s/h)

Regarding the comparison between the farms at each point of testing, the pigs on farm 1

played significantly longer than the pigs on farm 2 and farm 3 in the first fattening phase

(Figure 2). In the final fattening, significantly shorter durations of playing behaviour (s/h)

occurred on farm 1 compared to farm 2 and farm 3 (Figure 2).

Concerning the comparison between the points of testing within each farm, the pigs on farm 1

showed significantly more playing behaviour in the first fattening phase than in the final

fattening (Figure 2). The pigs on farm 2 played significantly shorter in the first fattening

47

phase than in the final fattening (Figure 2). On farm 3, there was no significant difference

observed between the first fattening phase and the final fattening (Figure 2).

In terms of the comparison between the genders, there were significantly longer durations of

playing behaviour (s/h) observed in the sows than in the castrates (sows: 2.8 ± 1.0 s/h vs.

castrates: 2.4 ± 1.0 s/h; p<0.05).

Relating to the comparison between the location (inside vs. outside area) on farm 2 and farm 3

the pigs showed significantly longer durations of playing behaviour (s/h) in the outside areas

than in the inside areas (outside: farm 2: 3.6 ± 1.0 s/h; farm 3: 4.4 ± 1.0 s/h vs. inside: farm 2:

1.2 ± 1.0 s/h; farm 3: 2.2 ± 1.0 s/h; p<0.05).

Figure 2: LS-Means and standard errors of the total duration of playing behaviour (s/h) during the fattening; a, b, c different letters indicate significant differences within the farm between the different points of testing (p<0.05); A, B, C different letters indicate significant differences between the farms within the different points of testing (p<0.05); 1.=First fattening phase; 2.=Final fattening.

48

Locomotor play (s/h)

In respect of the comparison between the farms at each point of testing, the pigs on farm 1

showed significantly more locomotor play (s/h) than the pigs on farm 2 in the first fattening

phase and there were no significant differences observed between the locomotor play (s/h) of

farm 1 and farm 3. The pigs on farm 2 showed less locomotor play (s/h) than the pigs on farm

3. In the final fattening, there occurred significantly shorter durations of locomotor play (s/h)

on farm 1 than on farm 2 and farm 3 (Table 2).

Concerning the comparison between the points of testing within each farm, on farm 1 the pigs

showed significantly more locomotor play in the first fattening phase than in the final

fattening. On farm 2, there were no significant differences between the total durations of

locomotor play (s/h) in the first fattening phase and in the final fattening. The pigs on farm 3

showed significantly more locomotor play in the first fattening phase than in the final

fattening (Table 2).

The comparison of gender of the total duration of locomotor play (s/h) showed longer

durations of locomotor play (s/h) in sows than in castrates, although this difference did not

reach significance (sows: 1.5 ± 1.0 s/h vs. castrates: 1.4 ± 1.0 s/h; p=0.06).

Table 2: LS–Means and standard errors (retransformed) of the total duration of locomotor play (s/h) and social play (s/h)

Point of testing Play

category

Farm 1

(n=138)

Farm 2

(n=54)

Farm 3

(n=36)

First fattening phase locomotor 2.27 ± 1.07A,a 1.37 ± 1.05a,B 2.04 ± 1.05A,a

Final fattening locomotor 0.79 ± 1.05A,b 1.67 ± 1.05a,B 1.39 ± 1.05B,b

First fattening phase social 6.64 ± 1.09A,a 1.24 ± 1.07a,B 2.09 ± 1.07a,C

Final fattening social 1.33 ± 1.07A,b 1.47 ± 1.08A,a 2.18 ± 1.07a,B

A, B, C different letters indicate significant differences between the farms within each point of testing (p<0.05); a, b different letters indicate significant differences within the farms between the different points of testing (p<0.05).

Social play (s/h)

Regarding the comparison between the farms at each point of testing, the pigs on farm 1

showed significantly longer durations of social play (s/h) than the pigs on farm 2 and farm 3

in the first fattening phase. Besides, there was less social play (s/h) observed on farm 2 than

on farm 3 (Table 2). In the final fattening, there were no significant differences of the social

49

play (s/h) of farm 1 and farm 2 whereby the pigs on farm 1 showed significantly less social

play (s/h) than the pigs on farm 3. On farm 2, there was significantly less social play (s/h)

than on farm 3 (Table 2).

In terms of the comparison between the points of testing within each farm, the pigs on farm 1

showed significantly longer durations of social play (s/h) in the first fattening phase than in

the final fattening. The comparison of social play (s/h) between the first fattening phase and

the final fattening presented no significant differences on farm 2 and farm 3 (Table 2).

Concerning the comparison between the genders, the sows indicated significantly longer

durations of social play (s/h) than the castrates (sows: 2.1 ± 1.0 s/h vs. castrates: 1.9 ± 1.0 s/h;

p<0.05).

DISCUSSION

The main aim of this study was to investigate whether the occurrence of playing behaviour in

fattening pigs in different housing systems is suitable to measure their positive emotions and

to obtain a better general understanding of their whole affective state.

Play categories

The pigs in the barren environment showed less variety in their playing behaviour than the

pigs in the enriched housing systems: they showed no play categories such as “pivoting”,

“hopping” and “rolling” in the first fattening phase and no “rolling” and no “chasing” in the

final fattening. These lack of variety in playing behaviour are based on Newberry et al.

(1988), who argue that pigs in intensive housing conditions are unable to express their full

repertoire of playful behaviour due to e.g. limitations of space and novel objects. Following

the hypothesis that playing behaviour occurs when animals are in positive emotional states

(Burghardt, 2005), these findings probably indicate fewer positive emotions in pigs housed in

such impoverished conditions whose playing behaviour is presumably hampered.

Total duration of playing behaviour

In the first fattening phase it is conspicuous that the pigs in the barren environment showed

considerably more playing behaviour than the pigs in the enriched housing systems. This may

be due to the different management of the two housing systems: farm 1 represented a closed

50

system, in which, the piglets changed their compartment and pens within the farm and not

through stressful transport by trucks as applied to farm 2 and farm 3. In contrast to the young

pigs in the enriched housing systems, the barren housed pigs did not have to get used to new

farmers, feeding systems and daily routines either. This holistic familiarisation with the new

situation might become a major cause of stress for the relocating pigs. Therefore, recently

experienced stress could be a reason for the lower occurrence of playing behaviour in the

enriched housing systems in the first fattening phase (Bateson, 2014). The fact that the rearing

phase was shorter in the enriched housed pigs than in the barren housed pigs might also

explain their lower occurrence of playing behaviour (s/h) at this level of age because,

according to several studies, weaning results in the decline of playing behaviour (e.g.

Donaldson et al., 2002). Presumably, these enriched-habitat pigs also suffered a relative

deterioration of their familiar habitat due to a less attractive stable system compared to the

piglet production farms where they were reared in extensive pasture conditions. This possibly

resulted in frustrated fattening pigs that did not feel well and thus performed less playing

behaviour (Le Floc'h et al., 2010; Siviy et al., 2006). Frustration also counts as a clear

indicator of poor welfare (Broom, 1991). According to this, it is conceivable that the absence

or lower occurrence of playing behaviour represents an affective state of the examined pigs,

which includes a lower number of positive emotions.

In the final fattening, the pigs in the barren environment (farm 1) showed significantly less

playing behaviour (s/h) than those in the enriched environment (farm 2 and farm 3).

Particularly on the basis of these results, it is conceivable that play stimulating circumstances

such as food enrichment, or sudden impressions such as windy weather or novel events

(Newberry et al., 1988), or the offering of straw-bedding or elements of unpredictability to the

environment (Špinka et al., 2001) dominate more likely in enriched housing systems such as

on farm 2 and farm 3. Based on these results, it could be assumed that the lower occurrence of

playing pigs in the barren environment (farm 1) reveals their affective states, which appear to

possess fewer positive emotions than those pigs in the enriched housing systems (farm 2 and

farm 3). Mainly the increased availability of space could explain the longer occurrence of

playing pigs in the enriched housing systems (farm 2 and farm 3) compared to the barren

environment (farm 1). The enriched housing systems offer the three respectively eight times

as much space availability for the pigs. These findings correspond with the view of Lawrence

(1987) that playing behaviour occurs when the environmental conditions are optimal.

Furthermore, there was no tail biting observed in the enriched housing systems, whereas this

51

behavioural disorder increasingly occurred in the barren environment (20% of the pigs were

affected by tail-biting (biter or victim)) especially during the final fattening that possibly

points to poor welfare (Brunberg, 2011) and could explain the lower occurrence of playing

behaviour of these pigs at this level of age.

Moreover, the proposal of enrichment such as straw-bedding and different vegetables and

fruits once a day might be reasonable for the increased playing behaviour in the pigs in the

enriched housing systems (farm 2 and farm 3) at the final fattening compared to the barren

environment (farm 1). Enrichment such as straw-bedding or special soil-based rooting areas

also provide opportunities for pigs to perform their natural living habits, which indicates an

important part of good welfare (Fraser, 2008) and could be assumed as an explanation for

enhanced playing in the enriched housed pigs. Vinke et al. (2005) observed juvenile mink

with access to a swimming pool performing more play behaviour, although it occurred outside

the pool. Also, pigs showed longer durations of playing, after receiving food enrichment such

as seeds scattered in straw and buried chocolate raisins (Dudink et al., 2006; Reimert et al.,

2013). Even Morméde et al. (1990) observed that piglets which are kept in a small area

without straw could be more frustrated and stressed in such a housing environment and

therefore display a lower frequency of playing behaviour. Additionally, in the enriched

housing systems, there was more playing observed in the highly stimulating outside areas than

in the inside areas, probably due to the seasonal influences (Newberry et al. 1988), the

unpredictability of the environment (Špinka et al., 2001) and sufficient space for locomotor

play, whereas the pigs might prefer the inside area mainly for resting and sleeping. Moreover,

Martin et al. (2015) claim that enriched housed pigs may develop a broader play repertoire

and the cognitive abilities needed to perform play behaviour earlier than pigs in less enriched

habitats. Consequently, it could be assumed that an enriched habitat leads pigs to augment

their playing behaviour that supposedly reflects the presence of positive affect and good

welfare (Ahloy-Dallaire et al., 2017).

In addition, the feeding method appears to influence playing behaviour. Burghardt (2005)

predicted that enhanced resource availability increases the play levels that correspond to the

lower total durations of playing behaviour (s/h) on farm 1 and farm 2 than on farm 3 in the

final fattening. On farm 1 and farm 2 there was an animal feeding space ratio of 1:4, whereas

farm 3 allocated the largest animal feeding space ratio of 1:1, so it was possible that all pigs

fed simultaneously. Thus, the incidence of playing increased with enhanced resource

52

availability when the pigs weighed over 100 kg (farm 1: 1.20 ± 1.08 (s/h) vs. farm 2: 2.27 ±

1.09 (s/h); farm 3: 2.75 ± 1.08 (s/h)) (Figure 3). Therefore, it might be inferred that housing

systems with adequate feeding space ratios lead to augmented playing behaviour in fattening

pigs, which is again suspected to improve welfare and might be able to generate and by doing

this display positive affective states (e.g. Bateson, 2014; Burgdorf and Panksepp, 2006).

Locomotor play

In the first fattening phase, the pigs on farm 1 (barren habitat) and on farm 3 (enriched

habitat) showed significantly more locomotor play (s/h) than on farm 2 (enriched habitat). In

the final fattening, there is a definite difference between the two housing systems concerning

the occurrence of locomotor play (s/h): the pigs in the barren habitat (farm 1) showed

significantly less locomotor play (s/h) than those in the enriched habitat (farm 2 and farm 3).

As already mentioned, the enriched housing systems offer the three respectively eight times

the space availability for the pigs, especially in the final fattening. This extra-space possibly

extends invitations to the pigs to perform increased locomotor-play that is also reflected by

the longer durations of this playing behaviour (s/h) in the enriched environment (farm 2 and

farm 3) at the final fattening. These findings again emphasise the assumption that playing

behaviour occurs when the environmental conditions are optimal (Lawrence, 1987). In the

first fattening phase, the pigs in the barren environment (farm 1) have approximately double

the space available as they legitimately need (30 - 50 kg: 0.5m² per pig (BMVEL, 2006)) so

they showed total durations of locomotor play (s/h) equivalent to the pigs on farm 3, which

represented one of the enriched habitats. The pigs on farm 2 had the least space availability in

the first fattening phase and therefore presumably performed the least locomotor play at this

level of age. Thus, the opportunity to perform playing, especially locomotor play due to

sufficient space, improves neuromuscular development, motor performance (Byers, 1977) and

cardiovascular fitness (Bekoff 1988; Byers and Walker 1995) resulting in enhanced health

that possibly points to increased welfare. Frequently performed locomotor play improves the

physical condition and authors argue that the better the physical condition in animals, the

more playing results (Sharpe et al., 2002; Nunes et al., 2004; Cameron et al., 2008).

Additionally, these findings might imply that housing conditions, which include sufficient

physical movement opportunities for the pigs, lead to increasing playing behaviour that

simultaneously might provide more possibilities for the developments of positive emotions.

As suggested in previous studies, play can produce affective states in terms of e.g. helping

53

individuals shed negative affective states (Calcagnetti and Schechter, 1992; Held and Špinka,

2011).

Social play

In the first fattening phase it is especially noticeable that the pigs in the barren environment

(farm 1) performed considerably more social play (s/h) than the pigs in the enriched housing

systems (farm 2 and farm 3). In contrast, this definite difference between the two housing

systems was not observed in the final fattening.

In the literature, the occurrence of social playing behaviour has been discussed

controversially. Hence, due to the studies of Hausberger et al. (2012) it could be possible that

the barren housed pigs of the present study showed significantly more playing behaviour

including a large amount of social play in the first fattening phase, because of being

chronically stressed by their low-stimulus environment. Hausberger et al. (2012) examined

the social play behaviour of captive horses and their physiological parameters such as

vertebral disorders, cortisol and oxidative stress values and linked significantly increased

occurrence of social play to poor welfare. In the study, socially playing horses showed more

vertebral disorders, higher oxidative stress values and behaved more aggressively towards

humans than non-social playing horses. Thus, social playing possibly also indicates an

opportunity for animals to cope with their usual, unfavourable life conditions (Hausberger et

al., 2012). This effect might detect a negative affective state of the coping animals, because

animals that are satisfied, e.g. with their environment, do not need to cope, e.g. in an

expression of a behavioural disorder such as belly nosing or sham chewing. As a

consequence, such non-coping animals possibly have a more positive affective state and

experience good welfare (Broom, 1991).

Gender

In the present study, significantly longer total durations of playing behaviour (s/h) occurred in

the female pigs than in the male pigs. This can be explained by different neurological

developments: according to Short and Balaban (1994), females show neurological

development earlier than male pigs and it is said that animals with increased and more

complex dendrite connections in the brain may be more likely to create their own play (Zupan

et al., 2016). Špinka et al. (2001) explained the gender difference based on the many disparate

abilities of motor skills between female and male pigs that influence how they play. It might

54

be also a long-term effect of injury and pain that decreases the playing behaviour of male pigs

due to their castration in early life. For instance, Winder et al. (2017) observed less playing

behaviour in calves in their group home pen after destruction of their horn buds using hot

irons than non-disbudded controls who had undergone a sham procedure. Even these results

may suggest that the lower occurrence of playing behaviour in animals which have recently

experienced negative emotions such as pain possibly indicate affective states including lower

numbers of positive emotions.

Moreover, the present results did not show significant differences in the occurrence of

locomotor play (s/h) between the genders although pursuant to studies of Brown et al. (2015),

there was more locomotor play (s/h) observed in the female pigs than in the male ones.

In this study, the male pigs showed significantly less social play than the females. In contrast,

Brown et al. (2015) observed no significant differences of the occurrence of social play

between the gender even though authors argue that playing behaviour is an important factor in

establishing social relationships in the future (Holmes, 1995), provided that males

traditionally compete for access to females for mating (Graves, 1984).

Age

Bekoff and Byers (1998) suggest that playing behaviour is characteristic of young mammals

and commonly observed at this age of life. Also, Brown et al. (2015) observed that playing

increased in the first six weeks of life and then declined to lower levels by week 14 of life.

The longer total durations of playing behaviour (s/h) on farm 1 and farm 3 in the first

fattening phase than in the final fattening confirm these studies although the difference of

these results on farm 3 did not reach significance. In the first fattening phase, the pigs on farm

1 and farm 3 also showed significantly more locomotor and social play (s/h) than the pigs in

the final fattening. Martin et al. (2015) observed heavier piglets performing less playing

behaviour than lighter piglets after weaning. Maybe the reverse situation on farm 2 is

explained by the holistic change of habitat and a stressful transport by truck as mentioned

above.

Experimental set-up

In addition to the presumed influencing factors on the occurrence of playing behaviour

mentioned, it cannot be excluded that the evaluative subjectivity of each observer also affects

55

the results of the pig’s playing behavioural observation, although intensively repeated courses

of instruction and a cross-classified application for each observer as well as a fixed effect of

the observer in the linear mixed model should minimise this impact. Besides this, the four

observers were not replaced during the whole analysis process of the video data.

CONCLUSION

The aim of this study was to investigate whether the occurrence of playing behaviour in

fattening pigs housed in different housing systems could be useful to obtain a better

understanding of their whole affective state. Following the various approaches of explanation,

playing behaviour might be capable of reflecting quite different emotional states. Thus, it

could be possible that the varied occurrence of playing behaviour in fattening pigs in different

housing systems constitutes a potential indicator of positive as well as negative affective

states including good or poor welfare. Nevertheless, due to the inconclusive results of the

present study and controversially discussed literature, it remains questionable as to whether

the occurrence of playing behaviour is capable of identifying exclusively positive affective

states in fattening pigs. Thus, a combination of further indicators could be useful to

compensate the consisting difficulties in the interpretation.

ACKNOWLEDGEMENTS




56

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63

CHAPTER THREE

Can tail and ear postures be suitable to capture the affective state of

growing pigs?




Submitted to Applied Animal Behaviour Science

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ABSTRACT

The present study examined whether tail and ear postures in fattening pigs (n=228) housed in

different housing systems could be suitable for assessing their affective state. In doing so, it

investigated the appearance of curled-up, hanging, raised, tucked-under or wagging tails

respectively ears directed forwards, backwards, mixed and laterally. The housing systems

examined included a barren (farm 1, n=138) and two enriched (farm 2, n=54; farm 3, n=36)

habitats that differed concerning the availability of space, enrichment and seasonal influences.

The tails of the pigs were undocked, and the boars were surgically castrated. The pigs’ tail

respectively ear postures were analysed for two days at the beginning and two days at the end

of fattening using the scan sampling method respectively the GLIMMIX procedure to analyse

the data. Especially at the end of fattening, the pigs in the barren housing system showed

significantly fewer curled-up tails than those in the enriched housing system (farm 1: 58.7 ±

11.6 % vs. farm 2: 91.6 ± 2.2 %; farm 3: 95.5 ± 1.8 %). The barren-housed pigs showed also

more raised respectively wagging tails than the enriched-housed pigs (raised tails: farm 1:

25.6 ± 7.6 % vs. farm 2: 1.3 ± 0.6 %; farm 3: 1.4 ± 0.6 %; wagging tails: farm 1: 8.7 ± 4.0 %

vs. farm 2: 3.4 ± 1.1 %; farm 3: 0.2 ± 0.2 %). Particularly at the end of fattening, there were

no definite differences concerning the ears directed forwards between the two housing

systems (end of fattening: Farm 1: 82.3 ± 8.5 %; Farm 2: 63.9 ± 4.9 %; Farm 3: 55.0 ± 6.1 %)

and significantly fewer ears directed laterally were observed in the barren than in the enriched

environment (farm 1: 11.3 ± 4.4 % vs. farm 2: 54.9 ± 3.9 % farm 3: 33.7 ± 3.2 %). Primarily

the curled-up tails could be suitable for indicating a positive affective state of the examined

fattening pigs whereas the other tail postures and principally the ear postures seemed to be

less suitable to reliably represent the pigs’ affective state due to inconclusive results between

the two different housing systems and controversially discussed literature. Nevertheless, the

findings of the present study improve the comprehension of the affective state in fattening

pigs in general.

Keywords: curled-up tails, ear postures, positive emotions, tail postures

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INTRODUCTION

Consumers are increasingly concerned about the welfare of animals, which contributes to the

decision on what products they buy. Thereby, it is widely accepted that good welfare is not

simply the absence of negative emotions (Boissy et al., 2007). Animal welfare scientists agree

that good welfare includes the promotion and provision of positive affective states and

experiences (Proctor and Carder, 2014). Hence, the study of emotions in animals has been

gaining interest (Panksepp, 1998). There is a wide agreement that animals can feel suffering

and pain and methods for assessing such negative emotions have been developed (Boissy et

al., 2007) but there is ultimately less knowledge of whether animals experience emotions

comparable to humans (Boissy et al., 2007). Nevertheless, scientific investigation of positive

emotions has long been omitted (Boissy et al., 2007). Hence, there is still a lack of established

methods for measuring the animals’ especially positive affective state which includes their

experienced emotions (Fraser, 2009). Therefore, it is an essential issue to become capable of

assessing whether and under what circumstances animals experience particularly positive

emotions (Boissy et al., 2007) and to know exactly which emotions animals can feel and how

they show them (Désiré et al., 2002). However, amongst other things, the subjective character

of short-term affective states as well as long-term mood makes their objective assessment

quite difficult (Curtis and Stricklin, 1991; Rushen, 1996). Hence, the development to measure

affective states as objectively as possible, especially by non-invasive and practicably applied

methods, remains a scientific challenge (Edwards, 2007; Winckler et al., 2007).

LeDoux (1996) states that the best objective and exact way to measure the affective state of

animals is to investigate physiological processes such as hormone transports or

neurotransmitter releases. Further, much more practical ways to assess the affective state of

animals seem to be behavioural observations. Authors suggest that behavioural parameters

such as playing behaviour, affiliative behaviour or vocalisations can be considered as

indicators of positive emotions in animals (Boissy et al., 2007). However, another potential

indicator of the animals’ affective state could be their tail posture, which is known to be

associated with pain or stress in calves and lambs (Graf and Senn, 1999; Grant, 2004). Tail

postures in pigs could conduce as an intraspecific communication method and in canid species

tail postures assist intraspecific signalling in different environments (Kleiman, 1972).

Whereas higher tail postures are suggested to be related to confidence or aggression, a lower

tail posture could reflect fear or submission (Tembrock, 1968; Fox, 1971; Kleiman, 1972;

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Prince, 1975; Bradbury and Vehrenkamp, 1998). Moreover, curled-up tails in pigs are

assumed to be linked to a positive affective state (Groffen, 2012) and Kiley-Worthington

(1975) concluded curled-up tail postures to be health indicators. Besides, Reimert et al. (2013)

described that tail postures of pigs varied depending on the emotional context. Thus, it might

be conceivable that different tail postures could be useful to gain a better understanding of the

animals’ affective state, including its positive and negative share.

Additionally, Boissy et al. (2011) observed that sheep ears rose up to upright positions during

negative situations whereas positive emotional experiences were related to passive, plane ear

postures. More forward ear postures of sheep were also found in negative experiences such as

social isolation and less in positive situations such as fresh hay feeding (Reefmann et al.,

2009). Additionally, a higher number of ear-posture changes seem to indicate negative

situations in pigs (Reimert et al., 2013). Also cows spend more time keeping their ears in

backward or hanging postures while being stroked, which could point to a more positive

affective state as other authors suggest that cows like to be stroked (Schmied et al., 2010,

2008a, 2008b; Waiblinger et al., 2004; Westerath et al., 2014; Windschnurer et al., 2009).

Hence, as there are highly developed muscles around the ears which ensure they can rotate in

many different ways (Reefmann et al., 2009), Reimert et al. (2013) assumed that ear postures

could be indicative of affective states in pigs.

Thus, the current study aims to promote the general understanding of the body language

signals of fattening pigs especially regarding their tail and ear postures and the associated

context to the pigs’ affective state.


Animals and housing

The study was conducted on three different farms in Northern Germany over a period from

November 2016 until September 2017. A total of 228 fattening pigs, bred from commercial

cross-bred dams (Large White x Landrace) and sired by Pietrain boars were used. All male

pigs were castrated, and the tails were undocked. The housing systems varied especially

regarding an enriched or barren habitat, the availability of space and the climatic conditions.

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The pigs in the enriched habitat were weaned at the age of six weeks and those of the barren

housing system were weaned with four weeks of life.

Farm 1 represented a conventional fattening stable (n=138) in a closed system in which the

pigs were housed in groups of 19 in a pen. These pens measured 3.70 x 4.70m resulting in

0.92m² per pig and the floor was half perforated and half concrete. Thus, farm 1 constituted

the barren habitat. There was an animal feeding space ratio of 1:4 and the pigs were fed ad

libitum with pelleted feed through dry-feeding machines. Water was achievable through

nipple drinkers and the ambient temperature was 18°C. Balls, plastic pipes and metal chains

were provided as occupation material and in case of tail-biting, the pigs received gunny sacks.

There was daily artificial light for eight hours (07:00-15:00).

Farm 2 (n=54) depicted an ecological fattening stable with an enriched environment, e.g.

inside and outside pens (in total 4.90 x 9.80m) with straw bedding. The outside pen involved a

roofed (2.70 x 4.90m) and roofless area (3.50 x 4,90m). In the first fattening phase, there were

54 pigs housed in one pen with a total area of 48.02m² (4.90 x 9.80m) occurring in 0.89m² per

pig. After the first fattening phase, the animals were divided into three of these pens evenly so

that each pig had 2.67m² available spaces. The feeding was ad libitum with mealy feed by an

animal feeding space ratio of 1:4.

The third farm (farm 3; n=36) exhibited an ecological fattening stable with an enriched

habitat. There were special soil-based rooting areas, roofed straw-bedded outside pens and

straw-bedded inside pens. The dimension of the whole pen was 83.32m² in total (8.33m² per

pig with a usual occupancy of 10 animals per pen). There was an animal feeding space ratio

of 1:1 and the pigs were fed ad libitum with liquid feeding.

In the enriched housing system (farm 2 and farm 3), there were hay racks and nipple drinkers

available as well but no occupation material as in the barren habitat (farm 1). The ambient

temperature and the daylight length were determined by the season. Supplementary, the pigs

in the enriched housing system got bread and different vegetables and fruits daily.

Experimental design

The present study investigated different tail and ear postures of fattening pigs at the beginning

and at the end of fattening of two batches from three different farms. The different tail and ear

postures were determined by an ethogram (Table 1).

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Table 1: Ethogram of the different tail and ear postures and presumed, related indicated affective state

Body part Tail/ear

posture

Description Presumed,

indicated

affective state

Reference

Tail

Curled-up

Tail forms a loop above the back of the pig

Positive e.g. McGlone et al. (1990)

Hanging

Tail is neither curled up nor raised but hangs down

Negative/neutral Paoli et al. (2016); Guthrie (1971)

Raised Tail is raised but not curled

Positive/Negative Scheurmann (1974); Reefmann (2009)

Tucked-under Tail is between the hind legs

Negative Groffen (2012)

Wagging Tail is wagging Positive/Negative Kleinbeck and McGlone (1993); Groffen (2012)

Ear

Forwards Ears are directed forwards

Positive/Negative Reefman et al., 2009; Raoult and Gygax (2018)

Backwards Ears are directed backwards

Positive/Negative

Windschnurer et al., 2009; Reimert et al. (2012)

Mixed

One ear is directed forwards and one ear backwards

Negative Reefmann et al. (2009)

Laterally

Ears are directed to the side, neither forwards nor backwards

Positive/Negative Reefmann et al. (2009);

Recording and analysis of the tail and ear postures

All fattening pigs were videotaped two days at the beginning and two days at the end of

fattening using camera systems (HeiTel Digital Video GmbH, Kiel, Germany and AXIS M30-

VE Network Cameras). The video cameras were positioned above the pens to obtain a

complete overview. Each of the pigs was marked individually with a sign on its back. By

using the scan sampling method (from the beginning of the daylight once an hour during the

same) the tail respectively ear posture of each pig was noticed if they were recognisable and

69

the pigs were walking or standing. Tail postures were classified as either “curled-up”,

“hanging”, “raised”, “tucked-under” or “wagging”. Ear postures were determined as “ears

directed forwards”, “ears directed backwards”, “ears mixed” or “ears directed laterally”

(Table 1). The video data were assessed by four observers. These observers were intensively

trained using video test sequences at the beginning of the video analysis and through repeated

courses of instruction between the individual evaluation sections. Additionally, the observers

were applied cross-classified and not replaced during the whole video analysis process.


Statistical analyses were performed with the SAS® 9.4 software (SAS Institute Inc., 2017).

The tail respectively ear postures were documented as binomial data (0 = respective tail or ear

posture was not shown; 1 = respective tail or ear posture was shown) during the video

analysis. The data were analysed using the GLIMMIX procedure with a binomial distribution

(link-function = logit). Fixed effects were added to the model in a stepwise manner. The

model for the data of the curled-up tails, hanging tails and ears directed forwards included the

fixed effects farm (1-3), points of testing (beginning respectively end of fattening) nested in

farm, gender (female, male) and a random effect of each individual pig nested in farm. The

model for the data of the raised tails, wagging tails and laterally directed ears included the

fixed effects of farm (1-3), gender (female, male) and a random effect of each individual pig

nested in farm. Statistical significance was determined at p<0.05 and the significance of

differences in the least square means was adjusted with the Bonferroni-correction. Due to rare

occurrences, statistical models could not be used for the data of the tucked-under tails, ears

directed backwards and ears mixed and therefore these results are not shown.

RESULTS

Curled-up tails

Regarding the differences between the farms at each point of testing, there were no significant

differences between the curled-up tails observed on farm 1 and farm 2 at the beginning of

fattening. On farm 1, there were significantly fewer curled-up tails than on farm 3. No

significant differences were observed between farm 2 and farm 3. At the end of fattening,

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there were significantly fewer curled-up tails on farm 1 than on farm 2 and farm 3 and there

were no significant differences between farm 2 and farm 3 (Table 2).

Concerning the differences between the points of testing within each farm, there were no

significant differences between the curled-up tails at the beginning and the end of fattening on

farm 1. On farm 2 and farm 3, there were significantly fewer curled-up tails at the beginning

than at the end of fattening (Table 2).

Table 2: LS-Means and standard errors of the different tail and ear postures

Tail/ear

posture Point of testing Farm 1 Farm 2 Farm 3

Curled-up

Beginning of fattening

31.5±10.2 % A,a 71.8±7.1 % AB,a 82.4±3.8 % B,a

End of fattening 58.7±11.6 % A,a 91.6±2.2 % B,b 95.5±1.8 % B,b

Hanging


18.7±7.8 % A,a 17.7±5.7 % A,a 14.1±3.1 % A,a

End of fattening 10.4±6.2 % A,a 5.5±1.7 % A,a 3.1±1.5 % A,b

Ears directed

forwards


80.5±7.6 % A,a 3.2±2.3 % B,a 65.7±4.5 % A,a

End of fattening 82.3±8.5 % A,a 63.9±4.9 % A,b 55.0±6.1 % A,a

Raised - 25.6±7.6 % A 1.3±0.6 % B 1.4±0.6 % B

Wagging - 8.7±4.0 % A 3.4±1.1 % AB 0.2±0.2 % B

Ears directed

laterally

- 11.3±4.4 % A 54.9±3.9 % B 33.7±3.2 % C

A, B, C different letters indicate significant differences between farms within each time of testing (p<0.05); a, b different letters indicate significant differences within farms between the different points of testing (p<0.05).

Hanging tails

Relating to the differences between the farms at each point of testing, at both the beginning

and end of fattening, there were no significant differences between the hanging tails observed

on the three different farms (Table 2).

In terms of the differences between the points of testing within each farm, there were no

significant differences between the hanging tails observed at the beginning and the end of

fattening on farm 1 and farm 2. On farm 3, the pigs showed significantly more hanging tails at

the beginning than at the end of fattening (Table 2).

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Raised tails

Concerning the differences between the farms, there were significantly more raised tails

observed on farm 1, than on farm 2 and farm 3. There were no significant differences between

farm 2 and farm 3 (Table 2).

Wagging tails

In terms of the differences between the farms, there were no significant differences between

the wagging tails observed on farm 1 and farm 2. On farm 1, there were significantly more

wagging tails than on farm 3. No significant differences were observed between farm 2 and

farm 3 (Table 2).

Ears directed forwards

In regard to the differences between the farms at each point of testing, there were significantly

more ears directed forwards observed on farm 1 than on farm 2, at the beginning of fattening.

There were no significant differences between farm 1 and farm 3. On farm 2, there were

significantly fewer ears directed forwards than on farm 3. At the end of fattening, no

significant differences were observed between the farms (Table 2).

Concerning the differences between the points of testing within each farm, there were no

significant differences between the ears directed forwards at the beginning and end of

fattening on farm 1. On farm 2, there were significantly fewer ears directed forwards observed

at the beginning of fattening than at the end. There were no significant differences of the ears

directed forwards between the beginning and end of fattening on farm 3 (Table 2).

Ears directed laterally

Relating to the differences between the farms, there were significantly fewer ears directed

laterally on farm 1 than on farm 2 and farm 3. There were significantly more ears directed

laterally on farm 2 than on farm 3 (Table 2).

Gender

With regard to the differences between the gender, there were significantly more raised tails

observed in the sows than in the castrates (7.1 ± 1.8 % vs. 2.1 ± 1.1 %; p=0.04). A gender

effect occurred exclusively with raised tails.

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DISCUSSION

The main aim of this study was to investigate whether the occurrence of different tail and ear

postures in fattening pigs in different housing systems is suitable to obtain a better general

understanding of affective state, particularly regarding its positive share. Two distinct

different housing systems were selected, as it was suggested that there might be significant

differences in the appearance of the pigs’ tail and ear postures in these two habitat types, in

order to conclude that the tail respectively ear postures could be able to indicate the pigs’

more positive affective state. It was hypothesised that the fattening pigs with a more positive

affective state were presumably housed on farms 2 and 3 due to a more enriched environment

compared to the barren habitat on farm 1. The enriched environment could be the potential

cause for this difference, as enrichment such as straw bedding or soil-based rooting areas

provide more opportunities for the pigs to perform their natural living, which constitutes an

important part of good welfare (Fraser, 2008) and possibly induces a more positive affective

state.

Curled-up tails

The barren-housed pigs showed significantly fewer curled-up tails than the pigs in the

enriched housing system especially at the end of fattening. Further, the enriched-housed pigs

in studies by Groffen (2012) indicated a curled-up tail more often than barren-housed pigs.

Other authors observed a positive correlation between feeding and drinking with a curled-up

tail. As feeding and drinking is known as positive behaviour that satisfies the essential need

for food and water (Cabanac, 1992; Carver, 2001; Rolls, 2005; Burgdorf and Panksepp, 2006)

it is possible that pigs curl their tails up when they are satisfied, which would indicate that

their affective state is more positive than negative. While there are usually more possibilities

to explore in enriched habitats than in barren housing systems, the curled-up tails observed

more often in the enriched housing system could be, as mentioned above, due to the satisfied

need of the pigs to perform their natural living, which constitutes an important part of animal

welfare (Fraser, 2008). This ability to perform natural behaviour and a simultaneous increase

in the occurrence of curled-up tails in more enriched environments could also indicate that

pigs, when they curl up their tails, are satisfied and therefore presumably possess more

positive affective states. Moreover, Goursot et al. (2018) observed pigs curling up their tails in

rewarding situations, which can be considered as positive experiences and therefore could

also indicate that pigs possess positive affective states when they curl up their tails. Moreover,

73

pigs showed their tails curled up more often in pens without a tail-biting outbreak than in pens

where this behavioural disorder occurred (McGlone et al., 1990). As tail-biting is known to

indicate poor welfare (Edwards, 2011) it is conceivable that the lower appearance of curled-

up tails and the simultaneous occurrence of the described behavioural disorder could point to

a less positive affective state. Also, Zonderland et al. (2009) observed pigs with curled-up

tails often lacking any tail damage, which might also indicate and promote more positive

affective states in these pigs as tail damage is associated with negative emotions such as pain;

presumably it reduces health and therefore might be able to lower the positive share of the

pigs’ affective state. Additionally, Kiley-Worthington (1975) concluded the appearance of

curled-up tails in pigs as a health indicator. Thus, according to the explanations above, it

seems acceptable that the occurrence of curled-up tails clearly points to a more positive

affective state in the enriched- than barren-housed pigs in this study.

Hanging tails

No significant differences between the hanging tails occurred in this study on the farms at the

different points of testing. Except on farm 3 where there were significantly more hanging tails

observed at the beginning than at the end of fattening.

However, according to literature, it could be possible that the occurrence of hanging tails

points to a less positive affective state in pigs. Thus, Paoli et al. (2016) suggest that a hanging

tail presents a defensive response to unwanted tail investigation involving tail-biting. Other

authors have also observed tail-biting occurring mostly when the pigs’ tails hang motionless

(Van Putten, 1980; Arey, 1991). As mentioned above, tail-biting constitutes a behavioural

disorder that points to poor welfare (Edwards, 2011). Moreover, hanging tail postures are also

known to be behavioural patterns of pain in piglets after tail docking (Noonan et al., 1994;

Sutherland et al., 2008). As pain is well known as a negative emotion, Groffen (2012) also

suggested a hanging tail posture to be linked to a more negative affective state. Thus, the

appearance of hanging tails after or during negative experiences could indicate a less positive

affective state in pigs. The significantly more hanging tails on farm 3 at the beginning than at

the end of fattening might be explained by a relative deterioration of their familiar habitat due

to a less attractive stable system compared to their piglet production farms where they were

reared in extensive pasture conditions, possibly resulting in frustrated fattening pigs that did

not feel well and thus performed more hanging tails in the beginning than at the end of

fattening (Le Floc'h et al., 2010).

74

Nevertheless, in ungulates (Guthrie, 1971) and in dogs (Tembrock, 1986; Fox, 1971;

Kleiman, 1972; Prince, 1975; Bradbury and Vehrenkamp, 1998), a hanging tail is seen as a

neutral tail posture, which is assumed to indicate neither positive nor negative affective states.

Hence, it should be noted that it could be difficult to conclude clearly whether hanging tails

indicate exclusively negative or also rather neutral affective states in pigs. However,

presumably, the aforementioned arguments of a hanging tail as an indication of a more

negative affective state might prevail, because a transferability of ungulates and dogs to

fattening pigs with respect to hanging tails could seem to be questionable. Contrary to the

hypothesis in this study, even though no significant differences were observed in the

occurrence of hanging tails between the two housing systems, further studies are needed to

investigate hanging tails as an indication of a more negative affective state in pigs.

Raised tails

There were significantly more raised tail postures observed in the barren housing system than

in the enriched housing system. In the view of Paoli et al. (2016), an upright tail posture

represents a welfare indicator in pigs, which is reduced when tail-biting occurs. Thus, it could

be assumed that a raised tail posture in pigs indicates a more positive affective state.

Moreover, calves (Scheurmann, 1974) and lambs raise their tails while sucking, and other

observations have shown raised tails in sheep while being groomed by humans (Reefmann et

al., 2009). Suspecting that sucking and being groomed are appreciated as positive stimuli, a

raised tail could also be able to indicate a more positive affective state in calves, lambs and

sheep. In contrast to this, raised tails might possibly also indicate a rather negative affective

state in sheep and ungulates. Reefmann et al. (2009) observed sheep raising their tails only

during separation from their herd members and not during rumination or pleasant situations

such as fresh hay feeding. By separation from the group, it is possible that animals feel

negative emotions such as fear and anxiety that promote a more negative affective state.

Additionally, feeding should be a positive experience that satisfies essential needs (Cabanac,

1992; Carver, 2001; Rolls, 2005; Burgdorf and Panksepp, 2006), which confirms the

assumption that more raised tails indicate rather negative affective states in sheep. Moreover,

in ungulates, a raised tail is linked with alarm and flight behaviour (e.g. Alados, 1986), which

could be associated with a more negative affective state as alarm and flight behaviour is

linked to negative emotions such as fear and stress. Additionally, it is said that a raised tail

75

shows a strong emotional activation in general, irrelevant of negative or positive valence

(Reefmann et al., 2009).

However, due to the overall context of this study and a questionable transferability from sheep

and ungulates to pigs, it is difficult to conclude clearly whether a raised tail indicates an

exclusively positive affective state in the examined pigs, although raised tails are assessed as

welfare indicators in pigs in literature. Based on the hypothesis of this study that the pigs with

the more positive affective state were housed on farms 2 and 3 due to their enriched

environment, more raised tails would have had to occur there than in the barren environment.

As this was not the case in this study and also more curled-up tails were observed in the

enriched than the barren environment and in literature curled-up tails clearly seem to be an

indication of a more positive affective state in pigs, the suitability of raised tails as reliable

indicators of a more positive affective state in the examined pigs of this study remains

questionable.

Wagging tails

On farm 1, there were significantly more wagging tails observed than on farm 3. According to

literature, tail wagging increases in food-frustrated situations (Kiley-Worthington, 1975) and

other authors have observed that tail-wagging increases shortly after surgical procedures

(Noonan, 1994; Hay et al., 2003) which are highly stressful and painful (Groffen, 2012).

Moreover, Zonderland et al. (2009) claimed that pigs often show more tail-wagging when

their tails are damaged presumably due to skin irritation (Kiley-Worthington, 1975).

Robertson et al. (1994) assumed that tail-wagging could be an effort to alleviate pain, e.g.

from biting insects or after being bitten by pen mates (Groffen, 2012). In addition to the

described assumptions of tail-wagging as an indication of a more negative affective state in

pigs, it is characterised as a sign of restlessness in cattle (Sylvester et al., 2004) and frustration

in antelope (Kiley-Worthington, 1978). In contrast, Kleinbeck and McGlone (1993) observed

that pigs wag their tail during feeding, which is seen as a positive experience and therefore

could be also associated with a more positive affective state in pigs. Additionally, also in dogs

tail-wagging is known to be linked to a positive affective state (Fatjó et al., 2007).

Furthermore, other authors assume that a wagging tail in black deer simply indicates arousal

and does not have any signalling characteristics (Stuart and Stuart, 1997). Thus, it might be

that also in pigs a wagging tail merely indicates arousal (Groffen, 2012). Hence, due to the

controversial discussions in literature and inconclusive results across the two different

76

housing systems regarding wagging tails in the fattening pigs examined, it is difficult to draw

a clear conclusion as to whether wagging tails could be potential indicators of a pig’s

exclusively more positive affective state.

Ears directed forwards

At the beginning of fattening there were significantly more forward ear postures observed on

farm 1 than on farm 2 and no significant differences occurred between farm 1 and farm 3. On

farm 2, there were significantly fewer ears directed forwards than on farm 3. At the end of

fattening, there were no significant differences between the ears directed forwards on the

three farms.

In studies of Reefmann et al. (2009), more forward ear postures in sheep were found in

negative experiences such as social isolation than in positive situations such as fresh hay

feeding. As social isolation from group members could induce negative emotions such as fear

and anxiety and fresh hay feeding might be able to induce positive affective states because it

satisfies essential needs for feeding and drinking as mentioned above, it could be assumed that

ears directed forwards indicate a less positive affective state in sheep. Also Proctor et al.

(2014) observed cows performing fewer forward ear postures during positive experiences.

However, it is questionable whether ears directed forwards point solely to a negative affective

state as this ear posture could also be linked to attentive animals (Raoult and Gygax, 2018),

which can also be achieved by positive stimuli.

Regarding the entire context of the results of this study and lacking sufficient literature

concerning the emotional context with ears directed forwards in pigs, it seems doubtful

whether the pigs on farm 2 showed conspicuously fewer ears directed forwards due to a much

more positive affective state at the beginning of fattening as described in sheep and cows. In

comparison with the results of the curled-up tails, which most probably indicate a positive

affective state due to clearly discussed literature, it could have been assumed that fewer ears

directed forwards would have also been observed on farm 3. However, since the observations

of the ears directed forwards respectively curled-up tails showed no consistent result and the

latter are clearly discussed as indications of a positive affective state in pigs, it seems as if

ears directed forwards have been hitherto less suitable to represent the affective state in pigs,

whether positive or negative.

77

Ears directed laterally

In the barren housing system, there were significantly fewer ears directed laterally observed

than in the enriched housing system. It seems imaginable that the ears directed laterally in the

present study could be related to both a passive ear posture (ears hanging down relaxed) or a

change in ear postures. Reimert et al. (2013) observed more ear posture changes in pigs in

aversive situations such as social isolation combined with negative, unpredictable

interventions, which could be an indication of a more negative affective state. Additionally, in

studies by Reefmann et al. (2009), fewer ear posture changes in sheep were associated with

positive situations (fresh hay feeding) and more ear posture changes with negative

experiences (social isolation). In opposite to this, higher numbers of passive ear postures in

sheep occurred more in positive than in negative situations (Reefmann et al., 2009).

In the overall view of the present study it might be imaginable that the ears directed laterally

point to a more positive affective state in the enriched-housed pigs, as there were also more

curled-up and fewer wagging tails observed, whereby particularly the former were assessed as

clearly indications of a more positive affective state in pigs. Nevertheless, it should be noted

that due to the snapshot of the scan sampling method, it cannot be unequivocally evaluated as

to whether the ears directed laterally in this study were related to ear posture changes or rather

passive ear postures and both presumably could be able to indicate negative respectively

positive affective states. Furthermore, the pigs’ ear postures could be less suitable to capture

the affective state in general, as there could be breed-specific differences in ear postures.

However, in this study, this can be excluded because the same genetics were housed on each

farm.

Gender

The more raised tails which were observed in the sows than in the castrates might be possibly

explained by external heat signs of the female pigs. Since the examined pigs were slaughtered

with an age of approximately six months, it may be that the sows had already shown first on

heat symptoms such as raised tails.

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CONCLUSION

The aim of this study was to examine whether different tail and ear postures of fattening pigs

housed in different housing systems could be suitable to obtain a better understanding of their

whole affective state and to identify reliable indicators to assess the pigs’ positive affective

state. Conclusively, primarily the curled-up tail postures might have the potential to assess the

affective state of the examined fattening pigs. Nevertheless, a combined consideration with

further indicators, e.g. physiological ones, would be useful to verify the suitability of the

curled-up tails as reliable indicators. However, the findings of the present study contribute to

the comprehension of the measurement of the positive affective state in pigs in general.

ACKOWLEDGEMENTS




79

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CHAPTER FOUR

Investigation of influence of growing pigs’ positive affective state on

behavioural and physiological parameters using

structural equation modelling




Submitted to Journal of Animal Science

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ABSTRACT

The aim of the present study was to investigate whether the primarily positive affective state

of fattening pigs influences various behavioural and physiological parameters such as the

pigs’ playing behaviour, way of behaving in behavioural tests, body language signals or

diameter and astroglia cell numbers of hippocampi, salivary Immunoglobulin A (IgA) content

or salivary protein composition. Additionally, the suitability of the variables mentioned was

examined to assess the pigs’ positive affective state in practice, which still constitutes a latent

variable not itself measurable. For this, a dataset including behavioural and physiological data

of 60 fattening pigs from three different farms with different housing systems were analysed

by the partial least squares structural equation modelling (PLS-SEM) method. A hierarchical

component model (HCM) was used including the pigs’ positive affective state as a higher-

order component (HOC) and the behavioural and physiological parameters as lower-order

components (LOC). Playing behaviour, body language signals and behavioural tests were

revealed, in this order, to be most influenced by the pigs’ positive affective state since these

resulted in the corresponding path coefficients (PC) of PC=0.83, PC=0.79 and PC=0.62,

respectively. Additionally moderate respectively almost moderate R²-values occurred for the

endogenous latent variables playing behaviour (R²=69.8 %), body language signals (R²=62.7

%) respectively behavioural tests (R²=39.5 %). Furthermore, the indicator of the “locomotor

play” showed the highest indicator reliability (IR) (IR=0.85) to estimate the latent variable of

pigs’ positive affective state. The results of the present study supplement the comprehension

and assessment of the pigs’ positive affective state in general.

Keywords: pig, positive affective state, positive emotions, structural equation modelling

INTRODUCTION

Partial least squares structural equation modelling (PLS-SEM) enables researchers to measure

latent variables, which are not directly assessable while measuring them indirectly using

indicator variables. Thus, it depicts a statistical method that facilitates the estimation and

testing of correlative relationships between dependent and independent variables and the

latent structures in between and aims to explain the highest possible variance of latent

variables by calculating various algorithms (Hair et al., 2017). SEM is used as a common

87

method in social science and marketing concerns, though its popularity has also increased in

agriculture issues (Lamb et al., 2011; Valente et al., 2013) such as milk production (de los

Campos et al., 2006; Heringstad et al., 2009) or animal welfare issues in gallop sports in

horses Müller et al., (2015). Hence, the positive affective state in livestock particularly still

constitutes a latent variable for which there is still no reliable measurement method. However,

there is the hypothesis that the positive affective state could influence different behavioural

and physiological parameters in livestock, so that it might be possible to make statements

about the affective state through the analysis of these possible impacts (e.g. Bosch et al.,

2004; Siviy et al., 2006; Czéh et al., 2006) and whether behavioural or physiological

parameters could be able to assess the positive affective state.

In the first instance, in behavioural tests, animals might react in certain ways in special test

situations, so that their type of behaviour, which e.g. seems to express fear (Forkman et al.,

2007), could possibly lead to conclusions about their affective state. Moreover, it has been

stated that playing behaviour only exists in animals if the animals fare well and feel well

(Siviy et al., 2006) and that it decreases when animals experience negative emotions

accompanied by e.g. threats to their fitness (Fagen 1976; Martin and Caro 1985; Burghardt

2005) or adverse environmental conditions (Müller-Schwartze et al., 1982; Siviy and

Panksepp, 1985) which could also allow conclusions concerning the affective state.

Additionally, the body language signals of animals could also be suitable to indicate their

affective state since e.g. the occurrence of curled-up tails in pigs are assumed to be linked to

their more positive affective state (Groffen, 2012). Moreover, there could be transferable

similarities between humans and pigs, so that it could be reasonable to use physiological

information on human depression research to assess livestock’s and in this case pigs’

primarily positive affective state. For instance, due to results from human depression research

it could be conceivable that pigs with a more positive affective state show higher contents of

salivary Immunoglobulin-A (IgA) (Bosch et al., 2004), larger diameters of hippocampi and

higher numbers of astroglia cells (Czéh et al., 2006) than pigs with a more negative affective

state.

Thus, in the current study, SEM was used to estimate the complex interactions between the

behavioural and physiological latent variables mentioned with regard to the particularly

positive affective state in fattening pigs and its influence on these parameters to obtain

indicators for a better understanding of the affective state of pigs in general.

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General scheme of a structural equation model (SEM)

A SEM includes two different types of variables which represent the relationships between

them. There are latent variables, which are not directly measurable, and latent measurement

variables, which make an estimation of the former latent variables possible. A SEM is formed

by a structural model (endogenous respectively exogenous latent variables) and at least two

measurement models (latent measurement variables and their self-characterising indicators).

The relationships (path coefficients (PC)) between the endogenous respectively exogenous

latent variables indicate the structural model by arrows connected to each other. Endogenous

(dependent) latent variables can be influenced by other latent variables, irrelevant of being

endogenous or exogenous, although exogenous (independent) latent variables cannot be

affected by other latent variables. Thus, the coefficient of determination (R²), which indicates

to which extent the latent variable is explained by other latent variables, is exclusively

computed for endogenous latent variables (Figure 1).

Hypotheses of the present SEM

This study examined the hypotheses that the primarily positive affective state of fattening

pigs’ influences behavioural and physiological parameters and that behavioural and

physiological parameters could be useful to estimate the pigs’ positive affective state.

Moreover, the positive affective state of fattening pigs depicts the latent variable, which is not

directly measurable, and the behavioural and physiological parameters form the latent

measurement variables, which enables an estimation of the pigs’ positive affective state. Thus,

the positive affective state is an exogenous latent variable and the behavioural and

physiological parameters are endogenous latent variables, which are influenced by the pigs’

positive affective state. According to literature, the animals’ affective state consists of

different emotions such as pleasure, happiness, pain and suffering and other feelings such as

hunger and thirst that are experienced as pleasant or unpleasant (Fraser, 2008). Moreover, the

primarily positive affective state presumably includes experienced pleasant emotions such as

happiness (Ortony and Turner, 1990; Diener and Lucas, 2000) whereas unpleasant emotions

such as fear, pain or suffering probably indicate the animals’ more negative affective state.

(a)

(b)

Figure 1: (a) general scheme of a structural equation model (SEM). IR=indicator reliability; (b) reflective-reflective hierarchical component model (HCM). IR=indicator reliability.

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Hierarchical Component Models (HCM)

The section above “General scheme of a structural equation model (SEM)” described first-

order models, which contain a single level of constructs. However, in other situations, as in

this study, very complex constructs have to be analysed. Such constructs require an

operationalisation at a higher abstraction level, so a hierarchical component model (HCM)

with two levels of abstraction was developed to analyse the construct of this study. The two

levels of abstraction of an HCM are the higher-order component (HOC), which assesses the

more abstract level, and the lower-order components (LOC), which include the sub-

dimensions of the higher component. Further, the pig’s affective state depicts the HOC, and

the different behavioural and physiological parameters represent the LOC. A reflective-

reflective HCM which contained a reflective relationship between the HOC and LOC was

used whereby all constructs of LOC were specified by reflective measurement models. A

reflective measurement model means that the indicators represent the underlying construct

and that the causality of the construct is directed to the indicators. In order to form the HOC

measurement model, all indicators of the LOC are also assigned to the HOC (Hair et al.,

2017) (Figure 1).

Assessment of the SEM

The SmartPLS 3.0 software (Ringle et al., 2015) was used to generate and calculate the SEM.

The evaluation was based on a variety of recommended quality criteria by Hair et al. (2017).

This evaluation involves a two-stage process whereby firstly the measurement models are

checked, followed by the structural model. Quality criteria of the measurement models

included the internal consistency reliability (composite reliability (CR)) and convergent

validity (indicator reliability (IR) and average variance extracted (AVE)). For the consistency

reliability, the composite reliability considers different loadings of indicators and displays

values between 0 and 1 whereas it should assume values between 0.6 and 0.7 in exploratory

research studies. For the convergent validity, the indicator reliability assesses how sufficient a

latent variable is estimated by an indicator. Thus, indicators with indicator reliabilities

between 0.4 and 0.7 should only be removed from the construct during the assessment process

if their removal increases the quality criteria of the model (Hair et al., 2017), whereas

indicators with indicator reliabilities below 0.4 should always be removed from the model

(Bagozzi et al., 1991; Hair et al., 2011). Further, the elimination of indicators should be

carefully considered as they should be retained if they make a corresponding contribution to

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the content validity of the whole model (Hair et al., 2017). AVE describes the extent to which

a latent construct explains the variance of its indicators and AVE should achieve values above

or equal to 0.5.

Primary quality criteria of the structural model involve the relevance and statistical

significance of path coefficients and the examination of the coefficients of determination (R²).

The path coefficients indicate the relationships between the constructs in the structural model

and correspond to the standardised regression coefficients in the regression analysis. Path

coefficients show values between -1 and 1 and verify or refute the pre-hypothesised

relationships between the constructs in the model. For this, sign and magnitude have to be

considered (Henseler et al., 2009). An estimated path coefficient near to +1 represents a

strong positive relationship between two examined constructs (and vice versa for negative

values), which is typically statistically significant. The closer the estimated path coefficient is

to 0, the weaker the relationship. Very low values close to 0 are generally not statistically

significant (Hair et al., 2017) whereby the statistical significance is tested by the

bootstrapping method. The coefficients of determination (R²) indicate the proportion of the

variance of an endogenous construct that is explained by all precursor constructs associated

with the endogenous construct. The higher the R² is, the better the construct is explained by

the latent variables in the structural model, which show structural path model relationships on

the explained construct (Hair et al., 2017). In scientific marketing research, R2-values of 0.25,

0.50 and 0.75 are assessed as weak, moderate and substantial, respectively (Henseler et al.,

2009; Hair et al., 2011).

Split-half scenario

To further assess the validity of the SEM, the split-half consistency was applied (Martin and

Bateson, 2007). After the SEM had been applied to the original dataset, this original dataset

was split into two halves by using the PROC SURVEYSELECT procedure in SAS® 9.4 (SAS

Institute Inc., 2017), to which the SEM was also applied.

Data origin and data structure

The dataset of the present study originated from 60 fattening pigs of two batches from three

different farms with two different housing systems in Northern Germany. SAS® 9.4 (SAS

Institute Inc., 2017) was used for the calculation of descriptive statistic. The dataset (n=60)

included behavioural data of two behavioural tests (human approach test (HAT) and novel

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object test (NOT)), playing behaviour (total duration, locomotor play and social play), body

language signals (curled-up, hanging, raised and wagging tails as well as ears directed

forwards, backwards, mixed and laterally) and physiological data of the saliva regarding its

Immunoglobulin A (IgA) content and protein composition (general protein content (GPC),

total number of bands (TNB) and total band intensity (TBI)) as well as physiological data of

the diameter and astroglia cell number of the hippocampi. The behavioural tests included

parameters of the approach latency (AL), duration of contact (DC) and number of contacts

(NC) in each test. AL represented the time in seconds that each pig needed to approach the

unknown human (in the HAT) or the novel object (in the NOT) until the snout touched the

human or the novel object. DC exposed the accumulated seconds in which the pigs touched

the human or the novel object with their snouts. The entire number of snout contacts that

occurred during the test phase was indicated by NC. The whole test phase was three minutes

and each pig was tested alone in the home pen. The unknown human in the HAT was always

a female person who the pigs did not know from daily routine work. A plastic duck presented

to the pigs in three different sizes (according to the age and the live weight of the animals)

represented the utilized novel objects in the NOT. These ducks showed a yellow body colour

with a red coloured beak. The behavioural data of the behavioural tests were recorded at the

beginning, middle and at the end of fattening and then summarised for each individual pig.

The playing behaviour involved parameters such as the total duration of playing behaviour,

locomotor play and social play in seconds per hour during the daylight of each pig. The body

language signals represented the prevalence of the curled-up, hanging, raised and wagging

tails as well as ears directed forwards, backwards, mixed and laterally once an hour during the

daylight of each individual pig. The behavioural data of playing behaviour and body language

signals were recorded for two days at the beginning and two days at the end of fattening. The

hippocampi diameters were measured in millimetres and the astroglia cell number in GFAP

pixel intensity. The IgA content (µg/ml) of the pigs’ saliva were analysed with a direct

quantitative sandwich-ELISA-Kit for pig-IgA (Celltrend GmbH, Luckenwalde, Germany).

The GPC (µg/ml) were analysed by colorimetric detection by means of a bicinchoninic acid-

based protein assay kit (Pierce™ BCA Protein Assay Kit, ThermoFisher Scientific Inc.,

Waltham, USA) and the TNB and TBI (px) through one-dimensional SDS-polyacrylamide gel

electrophoresis. All physiological data were collected merely at the end of fattening (Table 1).

During the selection process of data, it was considered that each variable contained less than

15 % missing values (Hair et al., 2014).

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The other two datasets (n=30; n=30) which were used for the split-half scenario included 30

randomly selected animals from the original dataset, respectively (PROC SURVEYSELECT).

Table 1: Descriptive data of indicators used in the SEM

Related

latent

variable

Indicator n

Mean Median Minimum Maximum Standard

deviation

Behavioural

tests

(endogen)

HAT-AL (s) 60 250.90 217.00 2.00 540.00 153.56 HAT- DC (s) 60 138.32 103.50 0.00 419.00 127.26 HAT-NC (s) 60 4.25 4.00 0.00 13.00 2.55 NOT-AL (s) 60 85.07 38.50 5.00 386.00 97.36 NOT-DC (s) 60 179.28 160.00 21.00 459.00 104.24 NOT-NC (s) 60 9.38 9.00 2.00 16.00 2.88

Playing

behaviour

(endogen)

Playing behaviour

(s/h) 60 27.81 20.67 0.00 112.88 26.50

Locomotor play

(s/h) 60 8.89 7.50 0.00 42.05 9.37

Social play (s/h) 60 18.88 10.32 0.00 102.88 22.26

Body

language

signals

(endogen)

Curled-up tails

(prevalence) 60 0.03 0.03 0.00 0.13 0.03

Hanging tails

(prevalence) 60 0.01 0.00 0.00 0.06 0.02

Raised tails

(prevalence) 60 0.01 0.00 0.00 0.13 0.02

Wagging tails

(prevalence) 60 0.00 0.00 0.00 0.06 0.01

Ears directed

forwards

(prevalence)

60 0.03 0.02 0.00 0.19 0.03

Ears directed

backwards

(prevalence)

60 0.00 0.00 0.00 0.01 0.00

Ears directed mixed

(prevalence) 60 0.00 0.00 0.00 0.02 0.00

Ears directed

laterally

(prevalence)

60 0.02 0.01 0.00 0.09 0.02

Slaughter

organs

(endogen)

Diameter of

hippocampi (mm) 60 5.27 5.38 4.25 6.50 0.52

Astroglia cell

numbers (GFAP

pixel intensity)

60 175.82 174.50 0.02 0.07 0.01

Saliva

(endogen)

IgA (µg/ml) 59 125.46 71.33 8.61 992.30 154.19 GPC (µg/ml) 60 1513.58 1185.64 341.97 4563.21 923.17 TNB 60 11.90 12.00 5.00 17.00 2.20 TBI (px) 60 392.86 381.65 146.31 1053.33 190.56

94

RESULTS

The subsequent sections present the results of the final SEM. An initial SEM was calculated

and then checked regarding quality criteria of measurement respectively structural models

which are explained in the previous section “Materials and methods”. To prove validity of this

final SEM, it was also applied to a second dataset (split-half scenario).

Initial SEM

The initial SEM estimated five relationships between six latent variables, divided into five

endogenous latent variables (LOC) and one exogenous latent variable (HOC). Thus, five

arrows connected one exogenous latent variable with five endogenous latent variables, which

served as latent measurement variables associated with 23 indicators (Figure 2).

Final SEM

In the final SEM, three relationships between four latent variables remained (three

endogenous latent variables (LOC) and one exogenous latent variable (HOC)). According to

the quality criteria of the indicator reliability, 17 of the initial 23 indicators were removed

from the model during the assessment process, as their loadings, which represent the

magnitude of indicator reliability, showed values below 0.4 or did not achieve statistically

significance (Hair et al., 2017). The endogenous measurement latent variable slaughter

organs, respectively saliva and their remaining associated indicators “astroglia cell numbers”

respectively “total number of bands” were in case of becoming a so-called single-item also

removed from the SEM as the use of single-items is risky, because it generally reduces

reliability and negatively impacts prediction validity (Hair et al., 2017) (Figure 3).

Assessment of the measurement models (final SEM)

The SEM measurement models were checked for reliability and validity based on the test

criteria composite reliability, indicator reliability and average variance extracted, which are

explained in “Materials and methods”. After calculating the first PLS-algorithm, all indicators

with loadings below 0.4 or without statistically significance were removed from the initial

model (Hair et al., 2017). For behavioural tests, the associated indicator “NOT-approach

latency” showed higher indicator reliability (IR=0.80) than the indicator “HAT-approach

latency” (IR=0.78). Thus, “NOT-approach latency”, appeared to be better than “HAT-

approach latency” to estimate behavioural tests. For playing behaviour, the indicator

95

“locomotor play” (IR=0.93) estimated the latent variable more sufficiently than the indicator

“total play” (IR=0.84). The relating indicators “curled-up tails” and “ears directed laterally”

of the body language signals indicated similar indicator reliabilities (IR=0.90 respectively

IR=0.90), which means that these two estimate body language signals equally well. For the

pig’s positive affective state, “locomotor play” (IR=0.85) was the most appropriate indicator

to estimate its latent variable, followed by “curled-up tails” (IR=0.71) and “ears directed

laterally” (IR=0.71), “total play” (IR=0.59), “NOT-approach latency” (IR=0.51), and “HAT-

approach latency” (IR=0.48) (Table 2).

As a next step, the reliability of the measurement models was examined using the composite

reliability. The measurement models behavioural tests had the lowest composite reliability

(CR=0.77) whereas playing behaviour and body language signals had the highest composite

reliabilities (CR=0.88 respectively CR=0.89). The composite reliability of the pigs’ positive

affective state (CR=0.81) was in between the above-mentioned values. As the composite

reliability was above 0.6 for all measurement models, all measurement models are proven to

be reliable (Table 2).

The test criterion average variance extracted was used to examine validity of the measurement

models. For all measurement models apart from pigs’ positive affective state, the average

variance extracted was above 0.5 (behavioural tests: AVE=0.63; playing behaviour:

AVE=0.79; body language signals: AVE=0.81); this proves the validity of all these

measurement models (Henseler et al., 2009). The value for the pig’s affective state

(AVE=0.43) is the lowest of all the measurement models and was close to the set threshold

(Table 2).

Assessment of the structural model (final SEM)

The evaluation of the structural model revealed that all relationships between the exogenous

and endogenous latent variables were statistically significant (p<0.05). Playing behaviour was

the most influenced parameter by the pigs’ positive affective state by indicating a path

coefficient of 0.83. After that, body language signals were more influenced by the pigs’

positive affective state than behavioural tests (PC=0.79 respectively PC=0.62).

The R²-values of the structural model were assessed in the following step. Here, the structural

model explained 39.5 % of the variance in behavioural tests, 62.7 % of the variance in body

language signals and 69.8 % of the variance in playing behaviour. Therefore, the structural

96

model best explains the variance of playing behaviour, followed by the variance of body

language signals and the variance of behavioural tests (Table 2).

Assessment of the split-half scenario SEM

Also the split-half scenario SEM1 and split-half scenario SEM2 were checked for reliability

and validity. As shown in Table 2, the test criteria of the split-half scenario SEMs indicated

similar tendencies as the results of the final SEM. The relationships (path coefficients)

between the exogenous and endogenous latent variables were statistically significant as well

(p<0.05).

Table 2: Indicator reliabilities (IR), coefficients of determination (R²), composite reliabilities (CR) and average variance extracted (AVE) of the final SEM, split-half consistency SEM1 and split-half consistency SEM2

Final SEM Split-half consistency SEM1 Split-half consistency SEM2

Latent

variable

Indicators IR CR AVE R² IR CR AVE R² IR CR AVE R²

Behavioural

tests

(endogenous)

HAT-

approach

latency

0.78

0.77 0.63 0.39

0.82

0.71 0.55 0.39

0.87

0.82 0.69 0.53 NOT-

approach

latency

0.80 0.65 0.80

Playing

behaviour

(endogenous)

Total play 0.84 0.88 0.79 0.69

0.91 0.92 0.85 0.77

0.76 0.84 0.72 0.69 Locomotor

play 0.93 0.93 0.93

Body

language

signals

(endogenous)

Curled-up

tails 0.90

0.89 0.81 0.62 0.85

0.86 0.76 0.60 0.88

0.87 0.78 0.61 Ears directed

lateral 0.90 0.89 0.88

Pigs’ positive

affective

state

(exogenous)

HAT-

approach

latency

0.48

0.81 0.43 -

0.52

0.82 0.44 -

0.66

0.82 0.44 -

NOT-

approach

latency

0.51 0.39 0.54

Total play 0.59 0.77 0.49 Locomotor

play 0.85 0.85 0.86

Curled-up

tails 0.71 0.62 0.68

Ears directed

laterally 0.71 0.73 0.69

Figure 2: Initial SEM. Circles indicate latent variables; rectangles represent indicators; arrows connecting circles represent relationships between latent variables (path coefficients); arrows between circles and rectangles indicate indicator reliabilities

Figure 3: Final SEM. Circles indicate latent variables; rectangles represent indicators; arrows connecting circles represent relationships between latent variables (path coefficients); arrows between circles and rectangles indicate indicator reliabilities; numbers in circles represent the coefficient of determination.

100

DISCUSSION

Assessment of the measurement models (final SEM)

Concerning indicator reliability, six of the initial 23 indicators were considered reliable for the

estimation of the respective associated latent variables. The high loadings (above 0.7) of the

indicators of the endogenous latent variables indicate that they all seem to be well suited to

measure their latent variable. The indicator reliabilities of the exogenous latent variable pigs’

positive affective state indicated values below 0.7 for the indicators “total play”, “NOT-

approach latency”, and “HAT-approach latency”. Nonetheless, these indicators were not

removed from the model, as indicators with indicator reliabilities between 0.4 and 0.7 should

only be removed from the construct if their removal increases the quality criteria of the model

(Hair et al., 2017). Further, the elimination of indicators should be carefully considered as

they should be retained if they make a corresponding contribution to the content validity of

the whole model (Hair et al., 2017), which was the case in this study. However, according to

the highest indicator reliability, the indicator “locomotor play” seems to be most appropriate

to measure the latent variable of the pigs’ positive affective state, followed by the indicators

“curled-up tails” and “ears directed laterally”, “total play”, “NOT-approach latency” and

“HAT-approach latency”.

These results seem to be realistic, as the occurrence of playing behaviour revealed to be

suitable to show a more positive affective state of the examined pigs. Also found in other

studies, playing behaviour only exists if animals fare well and feel well (Siviy et al., 2006)

and decreases when animals experience negative emotions accompanied by e.g. threats to

their fitness (Fagen 1976; Martin and Caro 1985; Burghardt 2005) or adverse environmental

conditions (Müller-Schwartze et al., 1982; Siviy and Panksepp, 1985). The fact that the

indicator “locomotor play”, according to the indicator reliabilities, seems to be the most

suitable for estimating the pigs’ positive affective state, could be related to the fact that the

opportunity to perform locomotor play improves neuromuscular development, motor

performance (Byers, 1977) and cardiovascular fitness (Bekoff 1988; Byers and Walker 1995)

resulting in enhanced health. This possibly points to increased welfare including experienced

positive emotions as basic health and biologic functioning depicts one of the most important

parts of animal welfare (Fraser, 2008) and affirms the presumably good suitability of

“locomotor play” to estimate the pigs’ positive affective state. However, the indicator “total

play”, which consists of the locomotor play and social play of the examined pigs, indicated

101

lower indicator reliability than “locomotor play”. This could be explained by the

controversially discussed literature regarding the occurrence of social play as an indication of

an exclusively positive affective state. Hausberger et al. (2012) linked the significantly

increased occurrence of social play in captive horses to poor welfare and therefore to a more

negative affective state. Thus, there is no definite evidence that social play indicates an

exclusively more positive affective state in the fattening pigs examined, even though the

transferability from horses to pigs could be questionable. However, it might explain the lower

indicator reliability of “total play” compared to “locomotor play”. Nevertheless, both

indicators of playing behaviour can be concluded as suitable indicators to estimate the latent

variable of the pigs’ positive affective state.

Hence, particularly the indicator “curled-up tails” of the body language signals seems to be

realistic to measure the pigs’ positive affective state, as according to literature pigs curl up

their tails in positive situations such as satisfying their essential needs for feeding and

drinking (Cabanac, 1992; Carver, 2001; Rolls, 2005; Burgdorf and Panksepp, 2006),

rewarding events (Goursot et al., 2018) or being housed in enriched environments (Groffen,

2012). Kiley-Worthington (1975) interpreted the appearance of curled-up tails in pigs even as

health indicators. Thus, it seems acceptable that curled-up tails could be suitable to estimate

the pigs’ positive affective state since satisfying essential needs, rewarding events, enriched

environments or good health presumably induce positive emotions and therefore a positive

affective state in pigs. As mentioned above, good health and biologic functioning represent

one of the most important part of animal welfare. The given opportunity to perform natural

living in enriched environments probably indicate enhanced welfare. In consequence, the

pigs’ positive affective state as natural living constitutes an important part of good welfare as

well (Fraser, 2008). According to the calculated indicator reliabilities, the ears directed

laterally also seem to be suitable to estimate the pigs’ positive affective state almost as well as

the curled-up tails. However, regarding this, further research is needed since it is imaginable

that the ears directed laterally of the present study could be related to both a passive ear

posture (ears hanging down, relaxed) or a change in ear postures. Further, Reimert et al.

(2013) observed more ear posture changes in pigs in aversive situations such as social

isolation combined with negative, unpredictable interventions, which could be an indication

of a more negative affective state. In opposite to this, higher amounts of passive ear postures

in sheep occurred more in positive than in negative situations (Reefmann et al., 2009). Thus, it

is difficult to conclude whether the ears directed laterally in the present study estimate an

102

exclusively positive affective state since due to the snapshot of the scan-sampling method, it

cannot be unequivocally evaluated whether the ears directed laterally in this study are related

to ear posture changes or rather passive ear postures. Both, presumably, could be able to

indicate negative respectively positive affective states.

Moreover, the indicators “HAT-approach latency” and “NOT-approach latency” of the

behavioural tests could be realistic to assess the pigs’ affective state. According to Brown et

al. (2009), quicker latencies to approach novel stimuli, such as unknown humans or novel

objects, are associated with less fearful animals. Therefore, it could be imaginable that

quicker approach latencies indicate pigs which possess a more positive affective state due to

less fearfulness. However, quicker approach latencies could also be a reason for a stronger

motivation to explore novel stimuli (Stolba and Wood-Gush, 1980) related to boredom in the

housing environment. This probably indicates pigs with a more negative affective state, since

then the pigs are possibly not able to perform their natural living, which depicts an important

part of good welfare (Fraser, 2008), as mentioned above. Based on these results and also due

to the controversially discussed literature concerning the ears directed laterally as well as

social play, it could also be assumed that the exogenous latent variable pigs’ positive affective

state corresponds more to the general affective state than to the primarily positive one.

Additionally, it seems quite understandable that according to the higher indicator reliability,

the indicator “NOT-approach latency” could be more appropriate to estimate the pigs’

positive affective state than the indicator “HAT-approach latency” as the pigs’ behaviour in

human approach tests can be influenced by their previous experiences with humans. There are

studies which demonstrate that negative handling leads to more avoidance responses (Carreras

et al., 2017). Hence, it could be conceivable that the pigs’ behaviour in the NOT is better

suited than the pigs’ behaviour in the HAT to estimate the pigs’ positive affective state.

Presumably, in further studies, it would be useful to include further indicators of behavioural

tests in the dataset, for instance related observations between quick approach latencies or

avoidance reactions, which could provide more detailed information on whether the pigs show

quick approach latencies due to less fear or a high motivation to explore unknown humans or

novel objects.

All values were above 0.6 for composite reliability, which indicates reliability in general

(Henseler et al., 2009). Thus, all four latent variables were sufficiently measured by their

respective indicators.

103

Three out of the four measurement models reached the recommended threshold for average

variance extracted, which states that AVE should be above than 0.5 (Henseler et al., 2009).

The average variance extracted for the exogenous latent variable pigs’ positive affective state

was 0.43, which is close to the mentioned threshold. An explanation for the lower average

variance extracted could be the lower indicator reliabilities of the indicators “HAT-approach

latency” (IR=0.48), “NOT-approach latency” (IR=0.51) and “total play” (IR=0.59).

Therefore, it could be possible that the pigs’ positive affective state is not sufficiently

estimated by these indicators, which could also indicate an insufficient estimation of the

whole exogenous latent variable of the pigs’ positive affective state. This, however, seems

obvious since this study is a first approximation, which does not exist in the form yet and

which lays the foundation for making the pigs’ affective state almost measurable and

understandable in the future. Conclusively, as mentioned above, additional indicators are

necessary to complement the estimation of the pigs’ positive affective state sufficiently. Also

Ringle (2004) advises modifying the measurement model when there are deficiencies in

discriminant validity, indicated by average variance extracted values below 0.5.

Assessment of the structural model (final SEM)

All three relationships between the exogenous and the endogenous latent variables showed

statistical significance according to the bootstrapping method. Thus, the pigs’ positive

affective state influenced all three endogenous latent variables significantly. Moreover, the

highest path coefficient between the pigs’ positive affective state and playing behaviour

indicated that this was the most influenced parameter (PC=0.83), followed by the body

language signals (PC=0.79) and behavioural tests (PC=0.62). This is in line with expectations

since also in previous literature playing behaviour has been suggested as suitable to indicate

good welfare and a positive affective state (Fagen, 1976; Lawrence, 1987; Boissy et al.,

2007). The results of path coefficients also show that the body language signals such as

curled-up tails respectively ears directed laterally as well as the pigs’ type of behaviour in the

behavioural tests are influenced by the pigs’ (positive) affective state. Hence, these results

also suggest that playing behaviour, the body language signals mentioned, and behavioural

tests could be potential indicators of a realistic assessment of the pigs’ positive affective state

in practice. All other parameters that were eliminated in the quality assessment of the SEM

therefore do not appear to be significantly influenced by the pigs’ positive affective state, and

therefore do not appear to be suitable for capturing the pigs’ positive affective state in

104

practice. This seems to be comprehensible especially with regard to the elimination of the

salivary parameters during the quality assessment of the model, since it is conceivable that the

saliva of the pigs may be affected by many factors such as different ingredients in the feed,

and especially the salivary IgA-content may rather be influenced by the health status of pigs

than by their positive affective state.

Concerning the coefficients of determination (R²), the model explained moderate R²-values

for the endogenous latent variables playing behaviour (69.8 %) and body language signals

(62.7 %) and an almost moderate R²-value for the endogenous latent variable behavioural

tests (39.5 %) (Henseler et al., 2009; Hair et al., 2011). This proves that the pigs’ positive

affective state explains the variance of playing behaviour and body language signals slightly

better than the variance of the pigs’ behaviour in the behavioural tests and could imply that

the former could be preferable to assess the pigs’ positive affective state in practice.

Additionally, it could be conceivable that behavioural tests are also influenced by the animals’

personality traits (Boivin et al., 1992) and not only by the affective state. However, further

indicators should be tested in the future and researched in other animal species to obtain a

more detailed understanding of the affective state.

Comparison of the final SEM with the split-half scenario SEM

Since the results of the split-half scenario SEMs indicated similar tendencies of test criteria

for reliability and validity as the final SEM does (Table 2), the model quality was assessed as

preserved. This confirms the overall validity of the final SEM that was used to pursue the

research issue of this study.

CONCLUDING STATEMENT

The current study is one of the first research studies using the PLS-SEM method for the

assessment of the pigs’ particularly positive affective state and its possible influence on

various behavioural and physiological parameters. This method seems to be suitable to

analyse the influence of the pigs’ positive affective state on behavioural and physiological

parameters and to assess the pigs’ positive affective state in practice. However, this study

which contributes to the understanding of the affective state in pigs in general depicts a first

approximation to estimate the pigs’ positive affective state using the PLS-SEM method.

105

ACKNOWLEDGEMENTS




106

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111

GENERAL DISCUSSION

The aim of this thesis was to obtain a better understanding of livestock’s particularly positive

affective state, exemplified by investigations with fattening pigs. On the basis of an analysis

of behavioural and physiological data of fattening pigs housed in two different housing

systems from three different farms, potential indicators were to be derived which would

enable feasible and reliable measurement of the pigs’ particularly positive affective state.

According to literature, the animals’ affective state contains different emotions such as

pleasure, happiness, pain and suffering and other feelings such as hunger and thirst that are

experienced as pleasant or unpleasant (Fraser, 2008). At this point, the primarily positive

affective state presumably includes experienced pleasant emotions such as happiness (Ortony

and Turner, 1990; Diener and Lucas, 2000), whereas unpleasant emotions such as fear, pain

or suffering probably indicate the animals’ more negative affective state. Hence, in the present

thesis, the question arose of when, under what circumstances and in what manner do

domesticated fattening pigs experience pleasant emotions such as happiness that can be

paraphrased by luck, joy, contentment or cheerfulness and thereby indicate a positive

affective state. That they can feel such complex emotions seems likely as they reveal similar

brain structures and chemistry to humans (Boissy et al., 2007) and it has been already

established that animals are able to experience basic emotions such as anxiety (Panksepp,

1998) as well as more complex emotions such as tension, nervousness, calmness or

contentment (Preston and de Waal, 2002).

First, it seems quite possible that the component ‘basic health and biologic functioning’ of

good animal welfare (Fraser, 2008) must be reached satisfactorily to attain a more positive

affective state as it is probable that alarmingly sick fattening pigs do not possess a completely

positive affective state. Therefore, housing systems and treatments that prevent disease and

suffering constitute an important requirement for the pigs to possess a positive affective state.

However, actually biologic functioning in the form of performance does not necessarily

contribute to a positive affective state, but only an animal that is healthy can show high

performance, which again implies that a more positive affective state requires biologic

functioning. Moreover, it might be possible that the component ‘natural living’ of good

animal welfare (Fraser, 2008) such as social contact to conspecifics or the opportunity to

perform innate natural behavioural patterns must also be complied so that the pigs can possess

112

positive affective states. Thus, a pig may have to wallow to possess a more positive affective

state, as it is an innate behavioural trait. This becomes even more prominent due to the fact

that conventionally raised domestic pigs show the same behavioural patterns as wild boars if

they have the opportunity (Stolba and Wood-Gush, 1989). In this regard, it appears likely that

housing systems that provide opportunities for the pigs to perform these behaviours probably

induce positive affective states. Continuously, it can be assumed that housing conditions

which offer the domesticated pigs a similar environment to that of wild boars could be those

housing systems which provide the best opportunity to obtain the most positive affective state

as possible. Therewith, a basic requirement of healthy animals must be fulfilled and natural

stress factors with which wild boars are confronted (e.g. foraging, food competition, hunters,

predators or extreme climatic influences) must be reduced to a minimum. Under natural

conditions, wild boars prefer the combination of different areas of the environment such as

open and dense forests, swamps and fields (Andersson et al., 2011) where they can perform

their major activities of sleeping, resting, rooting, feeding, standing and walking (Blassetti et

al., 1988). Accordingly, in this thesis, it was hypothesised that it might be possible for the

pigs housed in the enriched habitats including different functional areas on farms 2 and 3 to

possess a more positive affective state than the pigs of the barren housing environment of

farm 1 which contained only one functional area to live out all natural behavioural patterns.

Potential reliable indicators for the assessment of the pigs’ positive affective state

A variation of behavioural tests is known to be appropriate to assess the level of fear in

animals (e.g. Murphy et al., 2014; Hemsworth and Coleman, 1998) and focus on the

assessment of emotions (Carreras et al., 2017). Therefore, a human approach (HAT) and

novel object test (NOT) were selected to be applied to the pigs (Chapter One). As the

occurrence of playing behaviour is said to exist when animals experience positive emotions

(Fraser and Duncan, 1998; Špinka et al., 2001; Barnard, 2004; Burgdorf and Panksepp, 2006)

the pigs’ playing behaviour was also examined as a potential indicator to measure the pigs’

positive affective state (Chapter Two). In addition, certain body language signals such as the

pigs’ tail postures are described to vary depending on the emotional context (Reimert et al.,

2013) and therefore the occurrence of different tail and also ear postures (curled-up, hanging,

wagging, raised and tucked-under tails respectively ears directed forwards, backwards,

laterally and mixed) were investigated as well (Chapter Three). Further, the partial least

squares structural equation modelling method was used to identify the affective state’s

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influence on the parameters under observation as well as on further physiological parameters

and the potential suitability to measure the fattening pigs’ positive affective state of these

parameters (Chapter Four).

Behavioural tests

Especially at the end of fattening, the results of Chapter One showed consistent results

between the two different housing systems of the approach latencies in both behavioural tests,

which probably indicate the pigs’ more positive affective state in the enriched housing system

than the barren one. Higher approach latencies to come into contact with novel stimuli, such

as unknown humans or novel objects, are associated with more fearful animals (Brown et al.,

2009) and thus with a less positive affective state. However, the higher approach latencies

could also be a reason for less motivation to explore novel stimuli (Stolba and Wood-Gush,

1980) related to less boredom due to the enriched environment (Meagher and Mason, 2012),

which is then again an indicator of a more positive affective state. Simultaneously, barren-

housed pigs might be more motivated to explore a novel object or a person in the home pen

probably due to fewer exploration possibilities in their habitat compared to enriched-housed

pigs, which could explain the quicker approach latencies of the barren-housed pigs in this

study and presumably identify their less positive affective state. However, Forkman et al.

(2007) claim that the avoidance reaction of the animal appears to be essential as both a non-

curious and a fearful animal shows long latencies to approach, as mentioned above. It has

been also stated that the animals’ responsiveness towards humans and novel objects could be

considered to be rather an individual temperament trait (Gibbons et al., 2009) and not

dependent on the affective state. Therefore, it might be difficult to use the approach latencies

of HATs and NOTs as the sole indicators to measure the pigs’ positive affective state.

Including avoidance reaction or body language signals, such as the tail or ear postures during

the test situation, might enhance the possible informative power of these behavioural tests.

Furthermore, the implementation of a forced human approach test could be helpful (Pedersen

et al., 2003) in detecting the factual reason for the avoidance reaction (little interest or fear).

The forced human approach test might increase the likelihood of an animal responding more

actively to a human, whereas in the voluntary human approach test the chances of getting no

response or a passive response might probably be higher. Also the implementation of a forced

novel object test could be conceivable, which has also the advantage of minimising the impact

of the person who performs the behavioural test. Previous studies have shown that the pigs’

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behaviour in HATs can be influenced by their previous experiences with humans as there are

studies which demonstrate that negative handling leads to more avoidance responses (Carreras

et al., 2017), whereas positive handling might reduce the approach latency (Büttner et al.,

2018). Here, also higher approach latencies of male rather than female pigs in a HAT can be

explained by their castration and its consequences related to humans (Reimert et al., 2013a).

Additionally, the individual distance of each pig could also influence its behaviour in the

HAT (Rutherford et al., 2012) so that it is not necessarily fear that explains a high approach

latency but rather the character of the animal. Hence, it could be conceivable that the pigs’

behaviour in the NOT is better suited than the pigs’ behaviour in the HAT to estimate the

pigs’ positive affective state, which is confirmed by the indicator reliabilities of Chapter

Four. Additionally, the note of the pigs’ defecation and urination during the test phases could

be valuable as they could stand for negative experienced emotions in such test situations

(Forkman et al., 2007; Reimert et al., 2014). More elaborate in the application, but also useful

to receive more detailed information of the pigs’ affective state, could be the implementation

of cognitive bias tests. Here, animals with positive affective states behave also more

positively in new test situations compared to animals with rather negative affective states,

which can reveal cognitive bias tests as suitable indicators to assess affective states (Harding

et al., 2004). Furthermore, it could be investigated whether pigs which have been previously

positively conditioned to humans or novel objects approach them for instance with a curled-

up tail. This could combine the suitability of behavioural tests and body language signals as

an indication of the pigs’ affective state.

Another important consideration in further studies should be that all pens in which the pigs

are tested comprise the same size and design, which can possibly influence the pigs’

behaviour during the test situations (e.g. no hiding or feeding places). Here, it should be noted

that also the use of a home pen or a test pen and the test procedure at group or individual level

in behavioural tests could influence the tested pigs’ behaviour. For instance, an animal which

is tested alone could possibly show fear responses due to the effect of social isolation

(Forkman et al., 2007). Additionally, a test procedure at group level could probably hamper

the knowledge gained for each individual pig and also the habituation process in a test pen

could affect further behavioural responses (Forkman et al., 2007). Thus, when interpreting

results, it is important to consider how the behavioural tests were conducted, as each provides

advantages and disadvantages as described.

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Playing behaviour

Particularly at the end of fattening, the enriched-housed pigs showed longer total durations of

playing behaviour and solely locomotor play than the barren-housed pigs (Chapter Two).

Thus, it appears realistic that playing behaviour could depict a suitable indicator to measure

the primarily positive affective state in pigs as, for instance, it has been stated that animals

only show playing behaviour when optimal environmental conditions prevail (Lawrence,

1987; Held and Špinka, 2011) and they fare well and feel well (Siviy et al., 2006). Hence,

playing behaviour is known as “luxury” behaviour (Lawrence, 1987), which seems to

decrease when animals experience negative emotions (Fagen 1976; Martin and Caro 1985;

Burghardt, 2005) as it has been often described as being connected with animals experiencing

positive emotions (Fraser and Duncan, 1998; Špinka et al., 2001; Barnard, 2004; Burgdorf

and Panksepp, 2006). This confirms the assumption that playing behaviour represents a

reliable indication of a positive affective state, which is in accordance with the results of the

indicator reliabilities in Chapter Four. Mainly the enrichment of the environment (Špinka et

al., 2001) and increased availability of space could explain the longer occurrence of playing

pigs in the enriched housing systems compared to the barren environment in this study. Here,

further research studies should investigate whether an increased availability of space in barren

habitats also augments the occurrence of playing behaviour or whether it is primarily the

enrichment of the environment such as straw-bedding which causes the pigs to show more

playing behaviour. Here, the ground may also be an important factor which influences

whether the pigs show more playing behaviour as a slippery slatted floor probably does not

encourage the pigs to perform playing behaviour. The increased availability of space

presumably also enables more locomotor play of the enriched-housed pigs compared to the

barren-housed pigs, which is even more suitable than the total duration of playing behaviour

to assess the pigs’ positive affective state, as demonstrated by the structural equation model in

Chapter Four. This could be because the total duration of playing behaviour includes, apart

from locomotor play, also the durations of social play, which is possibly less suitable to

indicate the pigs’ especially positive affective state due to controversially discussed literature.

For instance, Hausberger et al. (2012) examined the social play behaviour of captive horses

and their physiological parameters such as vertebral disorders and linked significantly

increased occurrence of social play to poor welfare. In this study, socially playing horses

showed more vertebral disorders and behaved more aggressively towards humans than non-

socially playing horses. Thus, social play possibly indicates an opportunity for animals to

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cope with their usual, unfavourable life conditions (Hausberger et al., 2012) and reveals a

negative rather than positive affective state. In addition, it can be difficult to distinguish the

pigs’ social play from real fighting behaviour. Considering this, in further studies,

investigations of object play could be more suitable to obtain reliable information on the pigs’

primarily positive affective state, but it was not possible to compare this in the present thesis

as both housing systems did not provide the same opportunities for the pigs to perform object

play. Object play is defined by behavioural patterns when the animals manipulate, shake or

carry objects around (Newberry et al., 1988) and presumably is less impacted by a correct

detection or pen mates than social play and therefore possibly better suited than social play to

identify the pigs’ exclusively positive affective state more reliably. However, it might be

difficult to correctly distinguish object play from exploration behaviour, but this would less

affect the reliable detection of the positive affective state since the opportunity to perform

exploratory behaviour constitutes an important part of good animal welfare (Wood-Gush and

Vestergaard, 1990). Another important consideration in further studies should be to have the

same opportunities to record the required video data on all tested farms; so that a more

standardised analysis of the pigs’ performed playing behaviour is feasible. This could avoid

possible impact factors such as different daylight-length or visual qualities of the video data

which could influence the analysed playing behaviour. In addition, in future studies, it would

be preferable to examine the pigs’ playing behaviour on experimental farms including

completely standardised conditions, since also the management system – whether the farms

operate in a closed system or represent a pure fattening farm – can have impacts on the pigs’

behaviour. For instance, a relative deterioration of the familiar habitat due to another possibly

less attractive housing system could result in frustrated pigs which do not feel well and

therefore show less playing behaviour (Siviy et al., 2006; Le Floc'h et al., 2010).

Body language signals

Particularly at the end of fattening, the enriched-housed pigs showed more curled-up tails than

the barren-housed pigs (Chapter Three). This is in accordance with other studies in which

enriched-housed pigs indicated more often a curled-up tail than barren-housed pigs (Groffen,

2012). While there are usually more possibilities in enriched habitats to explore than in barren

housing systems, the more often observed curled-up tails in the enriched housing system

could be due to the satisfied need of the pigs to perform their natural living (Fraser, 2008).

This ability to perform natural behaviour and a simultaneous increase in the occurrence of

117

curled-up tails could indicate that pigs when they curl up their tails are satisfied and therefore

presumably possess a more positive affective state. Pigs with curled-up tails were also

observed in rewarding situations (Goursot et al., 2018), which can be considered as positive

experiences and therefore possibly indicate a more positive affective state as well. Moreover,

authors observed a positive correlation between feeding and drinking with curled-up tails,

which can also be considered a positive experience and, therewith, presumably indicate the

pigs’ more positive affective state. Thus, it seems acceptable that curled-up tails could be

potential indicators to identify the pigs’ positive affective state. Here, the results of Chapter

Four confirm this assumption. However, a key point to improve the experimental set-up

should be to combine the notification of the tail and ear postures with the related performed

activity at the point of scan-sampling as those presumably influence their meaning. For

instance, wagging tails were also observed during feeding (Kleinbeck and McGlone, 1993),

which are discussed controversially as an indication of an exclusively positive affective state.

In general, it may be difficult to assess the tail and ear postures during the feeding of pigs,

since, for instance, the animal feeding place ratio could also influence their meaning.

Moreover, regarding the predominant pig production conditions of intensive housing systems

in European countries in which the pigs’ tails are usually docked to protect them from injuries

by tail-biting, it is difficult to apply a curled-up tail as an indication of a more positive

affective state because docked tails cannot be curled up. Thus, only in housing systems where

the pigs’ tails are undocked could a curled-up tail be used to identify a more positive affective

state. Hence, deliberations could arise that pigs when they are not able to curl up their tails

can possibly possess a less positive affective state compared to pigs whose tails are undocked.

However, tail-docking is conducted on many farms with prior approval to protect the pigs

from injury and suffering caused by tail-biting, which presumably increases the positive

affective state rather than decreases it. Nevertheless, this deliberation seems also less realistic

as curled-up tails do not occur in wild boars (Jensen, 2002) although it could be conceivable

that wild boars, which seem to be able to perform their natural living almost unrestricted,

must show a curled-up tail in general. However, this non-appearance of curled-up tails in wild

boars could be explained by the fact that the pigs’ ability to curl up the tail developed during

the domestication process (Goursot et al., 2018).

The investigations of Chapter Four also indicated the ears directed laterally as suitable

indicator to assess the pigs’ positive affective state. However, this finding remains

questionable, as it seems imaginable that the ears directed laterally of the study in Chapters

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Three respectively Four could be related to both a passive ear posture (ears hanging down,

relaxed) or a change in ear posture. Reimert et al. (2013) observed more ear posture changes

in pigs in aversive situations such as social isolation combined with negative, unpredictable

interventions, which could be an indication of a more negative affective state. In contrast to

this, higher amounts of passive ear postures in sheep occurred more in positive than in

negative situations (Reefmann et al., 2009). Though it should be noted that due to the

snapshot by the scan-sampling method of the video data in the study of Chapter Three, it

cannot be unequivocally evaluated whether the ears directed laterally are related to ear posture

changes or rather passive ear postures and both presumably could be able to indicate negative

respectively positive affective states. Conclusively, it seems difficult to conclude clearly

whether the ears directed laterally can be due to the pigs’ more positive or rather negative

affective state, although the results of Chapter Four indicate this ear posture as a suitable

indicator. In further studies, this could be improved with more cameras from multiple

perspectives of the pen or the use of continuous sampling. With these improvements, it should

be easier to identify which position the ears need to be assigned to.

Conclusion and outlook

This thesis has shown that the approach latencies of both behavioural tests, total duration of

playing behaviour and locomotor play as well as curled-up tails could probably constitute

reliable indicators to identify the pigs’ particularly positive affective state. These indicators

revealed consistent results between both examined housing systems which are in accordance

with previous literature and can therefore draw conclusions concerning the pigs’ affective

state. Nevertheless, until now, primarily locomotor play and total duration of playing

behaviour as well as the curled-up tails have seemed to be reliable to measure the pigs’

positive affective state as the sole indicators. The approach latencies of both behavioural tests

in combination with the previously mentioned parameters appeared to be reliable to assess the

pigs’ particularly positive affective state. However, it is conceivable that these parameters,

especially the curled-up tails, could be integrated as feasible indicators into existing animal

welfare assessment systems to obtain a better understanding of the pigs’ positive affective

state.

In future studies, behavioural parameters such as e.g. the forced human-approach or forced

novel-object tests and cognitive bias tests should be further investigated regarding their

suitability to measure the pigs’ positive affective state. These parameters could be useful to

119

compensate the existing interpretation difficulties regarding high approach latencies and could

therefore capture the pigs’ positive affective state using behavioural tests as sole indicators

more reliably and conceivably complement the reliable suitability of other behavioural

parameters.

In closing, the conclusions presented in this thesis lay relevant foundations for the

understanding and measurement of the fattening pigs’ positive affective state. Further

research should supplement the studies of this thesis to obtain a better understanding of the

affective state in other animal species as well.

120

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GENERAL SUMMARY

The aim of this thesis was to derive potential indicators to attain a reliable measurement and

better understanding of livestock’s particularly positive affective state, exemplified by

investigations with fattening pigs. Diverse behavioural and physiological parameters were

examined regarding their suitability to assess the pigs’ primarily positive affective state in two

different housing systems on three different farms which differed especially in terms of an

enriched or barren environment, availability of space and climatic conditions.

In Chapter One, behavioural tests such as the human approach (HAT) and novel object test

(NOT) were investigated with regard to their usefulness to assess the fattening pigs’ positive

affective state. The pigs (n=297) were subjected to behavioural tests three times during their

fattening (begin, middle and end of fattening). They were tested alone in their home pen for

three minutes whereby three variables were analysed: the approach latency, duration of

contacts and number of contacts. Especially at the end of fattening, the enriched-housed pigs

showed higher approach latencies than the barren-housed pigs in both behavioural tests. The

HAT indicated lower durations of contacts in the enriched- than barren-housed pigs in

particular at the end of fattening but no clear differences between the two housing systems in

the NOT. For the number of contacts, there were no clear differences between the two

housing systems in both behavioural tests. The higher approach latencies could be due to less

motivation to explore novel stimuli related to an enriched environment with sufficient

opportunities to perform natural living. As natural living constitutes an important part of

animal welfare, the finding of the higher approach latencies in the enriched environment

might point to a more positive affective state of these pigs and could therefore represent a

potential indication of the same.

Chapter Two examined the occurrence of the pigs’ (n=228) total duration of playing

behaviour (durations of locomotor and social play in total), locomotor play and social play in

the two different housing systems. Video data from two days at the beginning and two days at

the end of fattening were analysed to obtain the durations of the different playing behaviours

during the day length (s/h) by the use of the continuous-sampling method. At the beginning of

fattening, the barren-housed pigs showed longer total durations of playing behaviour than the

enriched-housed pigs. At the end of fattening, an inverse situation existed as the enriched-

housed pigs showed longer total durations of playing behaviour than the barren-housed pigs.

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The locomotor play did not indicate clear differences between the two housing systems at the

beginning of fattening, but more locomotor play occurred in the enriched-housed pigs than the

barren-housed ones at the end of fattening. In contrast, at the beginning of fattening, the

barren-housed pigs showed more social play than the enriched-housed pigs and no clear

differences occurred between the two housing systems at the end of fattening. To conclude,

especially the consistent results of the total playing behaviour and locomotor play between the

two housing systems appeared to be suitable to determine the pigs’ positive as well as

negative affective states. This can be explained by the assumption that playing behaviour

increases when animals experience positive emotions and decreases when they are affected by

negative conditions. Due to controversially discussed literature and inconclusive results

especially at the end of fattening, social play did not reveal itself to be appropriate to assess

the pigs’ positive affective state.

In Chapter Three, the body language signals of the pigs (n=228) were assessed regarding the

occurrence of the different tail and ear postures (curled-up, hanging, raised, tucked-under or

wagging tails respectively ears directed forwards, backwards, mixed and laterally) in the two

different housing systems. Two days of the beginning and two days of the end of fattening

were analysed by using the scan-sampling method. Particularly at the end of fattening, the

enriched-housed pigs showed more curled-up tails than the barren-housed pigs. The barren-

housed pigs showed also more raised and wagging tails than the enriched-housed pigs.

Especially at the end of fattening were no clear differences of the ears directed forwards

between the two housing systems and the barren-housed pigs indicated fewer ears directed

laterally than the enriched-housed pigs. In this study, primarily the curled-up tails appeared to

be appropriate to assess the pigs’ positive affective state due to consistent results between the

two different housing systems and the assumption that the occurrence of curled-up tails is

related to satisfying situations. All other tail respectively ear postures were interpreted to be

less reliable to measure the pigs’ positive affective state related to their rare occurrence,

controversially discussed literature or inconsistent results between the two different housing

systems.

Chapter Four evaluated the relationships between the large variety of parameters for

behaviour (behavioural tests, playing behaviour and body language signals) and physiology

(diameters and astroglia cell numbers of hippocampi, salivary immunoglobulin-A content

respectively protein compositions) and the pigs’ positive affective state as well as its influence

127

on the parameters mentioned. The partial least squares structural equation modelling method

was applied to identify these relationships. The assessment of the coefficients of

determination (R²) evaluated the variables of the behavioural tests, body language signals and

playing behaviour to be influenced by the pigs’ positive affective state. The indicator

reliabilities revealed locomotor play, ears directed laterally, curled-up tails, playing behaviour

and approach latencies of both behavioural tests, in this order, to be the most appropriate

parameters to estimate the latent variable of the fattening pigs’ primarily positive affective

state. These findings are in accordance with the interpretations of the previous chapters and

confirm that the approach latencies of both behavioural tests, playing behaviour, curled-up

tails and especially locomotor play are potential indicators to measure the pigs’ positive

affective state reliably. Particularly the physiological parameters of this study appeared to be

less suitable to estimate the pigs’ positive affective state.

In summary, this thesis examined different methods and indicators with regard to their

suitability to assess the pigs’ positive affective state. Therewith, this thesis lays relevant

foundations to measure the affective state and contributes to its understanding in general.

129

ZUSAMMENFASSUNG

Das Ziel der vorliegenden Arbeit war die Identifizierung potentiell geeigneter Indikatoren, um

ein besseres Verständnis und eine zuverlässige Erfassung des positiven Gemütszustandes von

Nutztieren zu erlangen, wofür exemplarische Untersuchungen an Mastschweinen

durchgeführt wurden. Dazu wurden verschiedene verhaltensbezogene und physiologische

Parameter hinsichtlich ihrer Eignung einen positiven Gemütszustand der Schweine zu

identifizieren überprüft. Die untersuchten Mastschweine wurden auf drei Betrieben mit zwei

verschiedenen Haltungssystemen gehalten, wobei sich diese vor allem bezüglich der

reizärmeren oder reizvolleren Haltungsumgebung, des Platzangebotes pro Tier und der

klimatischen Bedingungen unterschieden.

Im ersten Kapitel wurde untersucht, ob der human approach (HAT) und novel object test

(NOT) dafür geeignet sind, einen positiven Gemütszustand der untersuchten Mastschweine

(n=297) zu erfassen. Die Verhaltenstests wurden mit jedem Tier an drei Zeitpunkten während

des Mastverlaufes durchgeführt (Vor-, Mittel- und Endmast). Hierbei wurden die Schweine

einzeln drei Minuten lang in ihrer gewohnten Bucht getestet, wobei drei verschiedene

Variablen analysiert wurden: die Annäherungslatenzzeiten, die Gesamtkontaktdauern und die

Anzahl der Kontakte. Insbesondere während der Endmast, zeigten sich in beiden

Verhaltenstests in der reizvolleren Haltungsumgebung höhere Annäherungslatenzzeiten, als in

der reizärmeren Haltungsumgebung. Zudem identifizierte der HAT vor allem in der Endmast

niedrigere Gesamtkontaktdauern der Mastschweine in der reizvolleren, als in der reizärmeren

Haltung. Im NOT zeigten sich hinsichtlich der Gesamtkontaktdauern jedoch keine deutlichen

Unterschiede zwischen den beiden Haltungssystemen. Bezüglich der Anzahl der Kontakte

entstanden keine eindeutigen Unterschiede zwischen den beiden Haltungsumgebungen in

beiden Verhaltenstests. Die höheren Annäherungslatenzzeiten könnten durch eine geringere

Motivation neue Stimuli zu erkunden bedingt sein, welche folglich im Zusammenhang mit

einer reizvolleren Haltungsumgebung und demnach ausreichenden Möglichkeiten natürliche

Verhaltensweisen auszuführen stehen. Da das Ausleben natürlichen Verhaltens einen

wichtigen Teil von Tierwohl darstellt, könnten die höheren Annäherungslatenzzeiten in der

reizvolleren Haltungsumgebung auf einen positiveren Gemütszustand dieser Mastschweine

hindeuten und gleichzeitig potentielle Indikatoren für diesen darstellen.

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Das zweite Kapitel fokussierte sich auf das Auftreten der Gesamtdauer des Spielverhaltens

(Gesamtdauer des lokomotorischen und sozialen Spielverhaltens) und des lokomotorischen

sowie sozialen Spielverhaltens der untersuchten Mastschweine (n=228) aus den zwei

unterschiedlichen Haltungssystemen. Hierbei wurde das Videomaterial von jeweils zwei

Tagen der Vor- und Endmast mithilfe der „continuous-sampling“ Methode analysiert, um die

Gesamtdauern des unterschiedlichen Spielverhaltens (s/h) zu erhalten. Während der Vormast

zeigten die Mastschweine der reizärmeren Haltungsumgebung eine höhere Gesamtdauer des

Spielverhaltens als die Tiere des reizvolleren Haltungssystems. Hingegen änderte sich dieses

Verhaltensmuster im Verlauf der Mast, sodass zum Zeitpunkt der Endmast in der reizvolleren

Haltungsumgebung höhere Gesamtdauern des Spielverhaltens auftraten, als in der

reizärmeren Haltungsumgebung. Bezüglich des lokomotorischen Spielverhaltens zeigten sich

während der Vormast keine eindeutigen Unterschiede zwischen den beiden

Haltungssystemen, wobei jedoch während der Endmast in der reizvolleren Haltungsumwelt

mehr lokomotorisches Spielverhalten gezeigt wurde, als in dem reizärmeren Haltungssystem.

Hinsichtlich des sozialen Spielverhaltens zeigten die Mastschweine der reizärmeren

Haltungsumgebung während der Vormast mehr soziales Spiel als die Tiere der reizvolleren

Haltungsumwelt, wobei jedoch während der Endmast keine deutlichen Unterschiede zwischen

den beiden Haltungssystemen auftraten. Schließlich könnten insbesondere die eindeutigen

Unterschiede der Gesamtdauer des Spielverhaltens und des lokomotorischen Spiels zwischen

den beiden Haltungssystemen geeignet sein, sowohl einen positiveren, als auch einen

negativeren Gemütszustand der untersuchten Mastschweine zu identifizieren. Diese Annahme

ergibt sich durch die Tatsache, dass Spielverhalten vermehrt auftritt, wenn Tiere positive

Emotionen erfahren und es sich verringert, wenn sie durch negative Bedingungen beeinflusst

werden. Hingegen zeigte sich das soziale Spielverhalten aufgrund von kontrovers diskutierter

Literatur und widersprüchlichen Ergebnissen zwischen den beiden Haltungssystemen

während der Endmast als weniger geeignet, um einen positiven Gemütszustand der

untersuchten Mastschweine zuverlässig zu erfassen.

Im dritten Kapitel wurden die körpersprachlichen Signale der Mastschweine (n=228)

hinsichtlich des Auftretens von verschiedenen Schwanz- und Ohrhaltungen (geringelte,

hängende, erhobene, eingeklemmte oder wedelnde Schwänze bzw. nach vorne, hinten,

gemischt und seitlich gerichteten Ohren) in den beiden Haltungssystemen analysiert. Hierfür

wurde das Videomaterial von jeweils zwei Tagen der Vor- und zwei Tagen der Endmast

mittels der „scan-sampling“ Methode untersucht. Vor allem während der Endmast wurden in

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der reizvolleren Haltungsumgebung mehr geringelte Schwänze beobachtet, als in der

reizärmeren Haltungsumwelt. Zudem zeigten die Schweine der reizärmeren Haltung mehr

erhobene und wedelnde Schwänze, als die Tiere des reizvolleren Haltungssystems. Außerdem

wurden insbesondere in der Endmast keine eindeutigen Unterschiede der nach vorne

gerichteten Ohren zwischen den beiden Haltungssystemen beobachtet und die Mastschweine

der reizärmeren Haltungsumgebung zeigten weniger seitlich gerichtete Ohren, als die Tiere

der reizvolleren Haltungsumwelt. In dieser Studie wurden vor allem die geringelten Schwänze

als geeignet interpretiert, um einen positiven Gemütszustand der untersuchten Mastschweine

zuverlässig zu erfassen. Dieses wurde insbesondere aufgrund von eindeutigen Ergebnissen

zwischen den beiden Haltungssystemen und der Annahme, dass geringelte Schwänze

vermehrt in zufriedenstellenden Situationen auftreten, geschlussfolgert. Die übrigen Schwanz-

und Ohrhaltungen wurden infolge von seltener Beobachtung, kontrovers diskutierter Literatur

oder widersprüchlichen Ergebnissen zwischen den beiden Haltungssystemen als weniger

geeignet identifiziert, um einen positiven Gemütszustand von Mastschweinen zu

identifizieren.

Das vierte Kapitel untersuchte die Zusammenhänge zwischen den verschiedenen

verhaltensbezogenen (Verhaltenstests, Spielverhalten und körpersprachlichen Signale) und

physiologischen (Durchmesser und Astrogliazellzahl von Hippocampi und Speichel-

Immunglobulin A Gehalt bzw. -proteinzusammensetzung) Parametern und dem positiven

Gemütszustand der Mastschweine sowie dessen Einfluss auf die genannten Parameter. Die

Methode der Strukturgleichungsmodellierung wurde angewendet, um diese Zusammenhänge

zu identifizieren. Hierbei zeigte die Bewertung der Determinationskoeffizienten (R²) einen

Einfluss des positiven Gemütszustandes von Mastschweinen auf die Verhaltenstests,

körpersprachlichen Signale und das Spielverhalten. Die Indikator Reliabilitäten identifizierten

das lokomotorische Spielverhalten, die seitlich gerichteten Ohren, die geringelten Schwänze,

die Gesamtdauer des Spielverhaltens und die Annäherungslatenzzeiten der Verhaltenstests in

dieser Reihenfolge als die geeignetsten Parameter um die latente Variable des positiven

Gemütszustandes von Mastschweinen zu schätzen. Diese Erkenntnisse entsprechen den

Interpretationen der vorherigen Kapitel und bestätigen die vermutete Eignung der

Annäherungslatenzzeiten der beiden Verhaltenstests, der Gesamtdauer des Spielverhaltens,

der geringelten Schwänze und insbesondere des lokomotorischen Spielverhaltens als

potentielle Indikatoren, um einen positiven Gemütszustand von Mastschweinen zuverlässig zu

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messen. Vor allem die physiologischen Parameter dieser Studie schienen weniger geeignet,

den positiven Gemütszustand der untersuchten Mastschweine zu erfassen.

Insgesamt wurden in allen Kapiteln dieser Arbeit verschiedene Methoden und Indikatoren

hinsichtlich ihrer zuverlässigen Eignung für die Beurteilung des positiven affektiven Zustands

von Mastschweinen untersucht. Somit legt diese Arbeit relevante Grundlagen für die Messung

des affektiven Zustands und trägt zu dessen allgemeinem Verständnis bei.

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ATTACHMENT

Material and Methods

The following sections contain a detailed summary of the material and methods used in the

present thesis.

Data collection

Data collection was conducted over a period from November 2016 until September 2017 in

two different housing systems on three farms in Schleswig Holstein and Lower Saxony,

Northern Germany. In the entire study, 302 crossbreed fattening pigs (Pietrain x (Large White

x Landrace)) from two batches were tested in total. The tails of the fattening pigs were

undocked, and the boars were surgically castrated. The main characteristics of the two

housing systems respectively three different farms are shown in Table 1. The housing systems

differed primarily in terms of space availability (m²/pig), an enriched or barren habitat and

climatic conditions.

Table 1: Overview of the farms included in the present thesis (LW=live weight)

Farm 1 Farm 2 Farm 3

Production system conventional/ closed system

ecological/ fattening stable

ecological/ fattening stable

Housing system barren enriched enriched Sample size

(in total)

160 106 36

Pigs/pen 19 54 (< 50 kg LW) 18 (> 50 kg LW)

10

Space/pig 0.92m² 0.89m² (< 50 kg LW) 2.67m² (> 50 kg LW)

8.33m²

Pen design inside pens floor: half-planed, half-perforated/ no bedding

inside/outside pens floor: straw bedding

inside/outside pens floor: straw bedding/ soil-based rooting area

Feeding ad libitum pelleted feed

ad libitum mealy feed/hay racks/vegetables and fruits

ad libitum liquid feed/hay racks/vegetables and fruits

Seasonal influence - yes yes

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The fattening pigs were tested three times during their fattening whereby the first, second and

third points of testing were at the beginning, middle and end of fattening, respectively. Table

2 shows which data were collected at each point of testing. During data collection, no major

changes in management or housing occurred on the three tested farms.

Table 2: Timings of data collection during fattening and sample sizes per farm (LW=live weight)

Start of fattening

(30 kg LW) Middle of fattening

(75 kg LW) End of fattening

(>100 kg LW) Sample size

per farm (n)

Farm

1

Farm

2

Farm

3

Farm

1

Farm

2

Farm

3

Farm

1

Farm

2

Farm

3

Behavioural

tests 160 106 31 160 106 31 160 106 31

Playing

behaviour 138 54 36 - - - 138 54 36

Body

language

signals

138 54 36 - - - 138 54 36

Saliva-

IgA content - - - - - - 25 15 19

Saliva-

protein

composition

- - - - - - 25 15 20

Diameter of

hippocampi - - - - - - 25 15 20

Astroglia

cell

numbers

- - - - - - 25 15 20

Experimental procedures

Behavioural tests

297 fattening pigs of two batches (farm 1: n=160; farm 2: n=106; farm 3: n=31) were tested in

three human approach (HAT) and three novel object tests (NOT), respectively at the

beginning, middle and end of fattening. The pigs were tested alone in their home pen. Both

behavioural tests were never conducted on the same day but always with a one-day time lag in

between. Each pig was given an acclimation period of two minutes followed by a test period

of three minutes that began when the unknown human entered, or the novel object was

brought into, the home pen. Always a female person whom the fattening pigs did not know

from daily routine work represented the unknown human in the HAT. She wore rubber boots

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and a clean overall and stood motionless in the middle of the home pen during the whole test

period. The utilized novel objects in the NOT were plastic ducks presented to the pigs in three

different sizes (related to the age and the live weight of the fattening pigs). These plastic

ducks indicated a yellow body colour with a red coloured beak. They were held in the middle

of the pen at the height of the pig's head by the use of a rod and a string. During the entire test

period, always the same observing person noted the analysed variables: the approach latency

(AL), the duration of contacts (DC) and the number of contacts (NC). AL was the time in

seconds that each pig needed to approach the unknown human or the novel object until the

snout came into contact with the human or the novel object. DC represented the summed

seconds in which the pigs touched the human or the novel object with their snouts. The entire

number of snout contacts that occurred during the test phase was shown by NC. If the pigs did

not come into contact with the human or the novel object, an AL of 180 seconds was noted.

Both behavioural tests were performed in the home pens of the respective farms. On Farm 1

the entire home pen (3.70 x 4.70m) was used. The amount of space for the fattening pig’s

testing on Farm 2 measured 6.20 x 4.90m with a roofed and unroofed area. On Farm 3, the

roofed outdoor area was utilised (2.40 x 3.80m) for both behavioural tests.

Video data of playing behaviour and body language signals

The same video data were used for the analysis of playing behaviour and body language

signals. 228 fattening pigs (farm 1: n=138; farm 2, n=54; farm 3, n=36) were videotaped for

two days at the beginning and two days at the end of fattening. The camera systems HeiTel

Digital Video GmbH, Kiel, Germany and AXIS M30-VE Network Cameras were used to

record the pigs’ behaviour. The cameras were positioned above the pens to obtain a complete

overview. All pigs were marked individually with a sign on their backs.

Training of the video observers

Due to the great extent of the video data, it was assessed by four observers. At the beginning

of the video analysis, these observers were intensively trained using video test sequences and

through repeated courses of instruction between the individual evaluation sections. Moreover,

these observers were applied cross-classified and no observer was replaced during the whole

video analysis process.

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Playing behaviour

The playing behaviour was examined for two days at the beginning and two days at the end of

fattening by an ethogram (Table 3) basing on previous literature research. The continuous

sampling method was used to note the duration (s/h) of each playing behaviour sequence. If

several pigs showed playing behaviour simultaneously, the video sequence was analysed for

one pig and then rewound and analysed for the other pigs. Relating to the testing environment,

the collected video material was analysed following the different play categories (Table 3) for

eight hours per day for farm 1 and accordant to the season for the daylight hours for farms 2

and 3. In order to obtain a comparable attribute, the total duration of playing behaviour was

divided by the light day per hour, resulting in the total duration of playing behaviour in

seconds per hour. This procedure was also conducted to obtain the total durations of playing

behaviour (s/h) for each play category (Table 3). The total duration of the locomotor play

(s/h) involved all play categories that were shown exclusively by body movements and the

total duration of the social play (s/h) included all play categories with additional social issues

(Table 3).

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Table 3: Ethogram of pigs’ playing behaviour

Play category Code Description References

Locomotor play Pivot a Gambolling or twirling the body

by 1 to 360° Brown et al. (2015), Chaloupkova et al. (2007), Donaldson et al. (2002), Newberry et al. (1988)

Hop b Jumping off with the hind legs and angling the forelegs

Welker (1961)

Scamper c Energetic running (from 1m or along the whole pen)

Brown et al. (2015)

Flop d Dropping from an upright to a lying or sitting position on the pen floor

Brown et al. (2015), Chaloupkova et al. (2007), Donaldson et al. (2002)

Roll e Rolling lengthwise over the back Defined for this study Head-shaking j Moving the head back and forth

quickly with ears flapping Reimert et al. (2013)

Social play Non-harmful fighting g Heads and mouths playfully

touching each other (no pushing anti-parallel/ without apparent aggression)

Brown et al. (2015)

Chase h Chasing other pigs playfully (without apparent aggression)

Welker (1961)

Invitation i Pushing the snout with minimal or moderate force into another pig’s body (if playing resulted afterwards)

Martin et al. (2015)


The fattening pigs’ body language signals were examined for two days at the beginning and

two days at the end of fattening followed by an ethogram (Table 4) based on previous

literature research. Through the usage of the scan-sampling method (from the beginning of the

daylight once an hour during the same) the tail respectively ear posture of each fattening pig

was recorded whether they were recognisable, and whether the pigs were walking or standing.

Tail postures were determined as either “curled-up” (the tail forms a loop above the back of

the pig), “hanging” (the tail is neither curled up nor raised but hanging down), “raised” (the

tail is raised but not curled), “tucked-under” (the tail is between the hind legs) or “wagging”

(the tail is wagging). Ear postures were classified as “ears directed forwards” (ears are

directed forwards), “ears directed backwards” (ears are directed backwards), “ears mixed”

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(one ear is directed forward and one ear backward) or “ears directed laterally” (ears are

directed to the side, neither forwards nor backwards) (Table 4).

Table 4: Ethogram of the different tail- and ear postures and presumed related indicated affective state

Body part Tail/ear

posture

Description Presumed

indicated

affective state

Reference

Tail

Curled-up

Tail forms a loop above the back of the pig

Positive e.g. McGlone et al. (1990)

Hanging

Tail is neither curled up nor raised but hanging down

Negative/Neutral Paoli et al. (2016); Guthrie (1971)

Raised Tail is raised but not curled

Positive/Negative Scheurmann (1974); Reefmann (2009)

Tucked-under Tail is between the hind legs

Negative Groffen (2012)

Wagging Tail is wagging Positive/Negative Kleinbeck and McGlone (1993); Groffen (2012)

Ear

Forwards Ears are directed forwards

Positive/Negative Reefman et al., 2009; Raoult and Gygax (2018)

Backwards Ears are directed backwards

Positive/Negative

Windschnurer et al., 2009; Reimert et al. (2012)

Mixed

One ear is directed forward and one ear backward

Negative Reefmann et al. (2009)

Laterally

Ears are directed to the side, neither forwards nor backwards

Positive/Negative Reefmann et al. (2009);

Physiological data of the present thesis

Out of the 302 fattening pigs examined in total, 60 animals were selected (farm 1: n=25; farm

2: n=15; farm 3: n=20) which definitely provided hippocampal data and less than 15 %

missing variable values (Hair et al., 2014) of all other behavioural (behavioural tests, playing

behaviour and body language signals) and physiological (salivary immunoglobulin A-content

139

respectively protein composition) parameters. This dataset was utilised to analyse the most

appropriate behavioural or physiological parameter to estimate the latent variable of the pigs’

positive affective state by using the partial least squares structural equation modelling method.

Saliva samples

Two saliva samples per pig were collected at the end of fattening when the pigs had a body

weight of about 100 kg. A synthetic fibre role was used for each sample (Cortisol-Salivette®,

Sarstedt AG & Co, Nümbrecht – Germany) and was presented to the pigs with a tweezer. The

fattening pigs had to chew it until it was completely salivated. Then, the samples were marked

individually and frozen immediately.

Saliva - Immunoglobulin A (IgA)

For the analyses of IgA, one of the saliva samples of each pig was thawed at room

temperature and centrifuged at 1000xg for 2 minutes. Hereafter, the supernatant was analysed

with a direct quantitative sandwich-ELISA-Kit for pig-IgA (Celltrend GmbH, Luckenwalde,

Germany).

Saliva - Protein composition

After thawing the insalivated synthetic fibre role at room temperature and centrifuging at

1000xg for 2 minutes, the general protein content (GPC) (µg/ml) were analysed by

colorimetric detection by means of a bicinchoninic acid-based protein assay kit (Pierce™

BCA Protein Assay Kit, ThermoFisher Scientific Inc., Waltham, USA) and the total number

of bands (TNB) and total band intensity (TBI) (px) through a one-dimensional, SDS-

polyacrylamide gel electrophoresis, followed by a modified method of Lamy et al. (2008).

Eight to 16% Mini-PROTEAN® TGX™ Precast Protein Gels (Bio-Rad Laboratories, Inc.,

Hercules, USA) were used to analyse 20 µg of protein per pig in a dual approach. The

required values including this protein amount were identified through the further results of the

general protein content. The samples were concentrated with a concentrator (Concentrator

plus, Eppendorf AG, Hamburg, Germany) if a greater saliva volume was needed to reach 20

µg protein as the wells had a maximal capacity of 20 µl. After implementation on the gels, the

samples ran at 40 volts for 15 minutes and then at 100 volts for 75 minutes. The gels were

then fixed with 50 ml of fixing solution for 20 minutes and stained with 50 ml of staining

140

solution for 30 minutes. Subsequently, the gels were photographed after being destained in

10% acetic acid for 46 hours.

The GelAnalyzer 2010a software (Lazarsoftware) was used to analyse the pictures by

extracting two parameters: the TNB for each lane and each pig and the intensity of all bands

TBI for each pig. The bands weights were specified by a marker (Precision Plus Protein™

Dual Xtra Standard, Bio Rad Laboratories GmbH, München, Germany) and then the intensity

of each individual band was identified by the area under the peak (AUP) in pixels (px). The

TNB depicts the mean of the sum of bands of both lanes for each pig, whereas the TBI

represents the mean of the intensities of all bands of both lanes of each pig.

Slaughter organs - hippocampi

Both hemispheres of the brains were taken separately from the carcasses during the

slaughtering process and were fixed in 4% paraformaldehyde for three days. After fixation,

the hippocampi of each hemisphere were removed, and 5 mm vertical slices were cut out and

transferred to 1% paraformaldehyde. Afterwards, the samples were embedded in paraffin

blocks and cut again into 50 µm slices by use of a microtome (RM 2155, Leica Biosystems,

Nussloch, Germany) and stained with a glial fibrillary acidic protein (GFAP)

immunohistochemistry. Then, four sections of every individual (two sections per hemisphere)

were analysed and averaged. The diameter from a line between the ventral expression of the

dentate gyrus and the CA3 region of the hippocampus proper to the middle of the CA1 region

was measured for the analyses of the hippocampal size. Pictures of the dorsal expression of

the dentate gyrus were taken at 10-fold magnification (Axiophot, Carl Zeiss Microscopy

GmbH, Jena, Germany) by the use of the AxioVision Rel. 4.8 software (Carl Zeiss

Microscopy GmbH, Jena, Germany) to detect the astroglia cell number. Hereafter, the

staining intensity of the pictures was assessed semi-quantitively with the ImageJ software

(National Institutes of Health, Bethesda, Maryland, USA). The resulting GFAP-staining-

pixel intensities were negatively correlated with the number of GFAP-expressing cells.

Statistical procedures

Statistical analyses for the behavioural tests, playing behaviour and body language signals

were performed with the software package SAS® 9.4 (SAS Institute Inc., 2017) using linear

mixed models respectively generalised linear models. The fit statistics AICC “Akaike’s

information criterion corrected” and the BIC “Bayesian information criterion” were proved to

141

evaluate the fitting of the statistical models. Fixed effects were added in a stepwise manner to

the models. The models with the smallest AICC and BIC values were chosen. The

significance of differences in the least square means was adjusted with the Bonferroni-

correction. Statistical significance was determined at p<0.05.

The SmartPLS 3.0 software (Ringle et al., 2015) was used to generate and calculate the partial

least squares structural equation model to investigate the influence of the fattening pigs’

positive affective state on the variety of behavioural and physiological parameters and to

analyse the most appropriate parameters to estimate the latent variable of the pigs’ positive

affective state. The evaluation was based on a variety of recommended quality criteria by Hair

et al. (2017).

Behavioural tests

The behavioural test data were not normally distributed. Thus, all data were log10 (X + 1)

transformed to obtain normality of residuals of the used linear mixed model (PROC MIXED).

The model used included the fixed effects farm (1-3), batch (1, 2) nested in farm, points of

testing (beginning, middle and end of fattening) nested in farm and gender (female, male)

together with a random effect of each individual pig nested in farm, batch and gender. The

residuals of the linear mixed models of all behavioural variables of both behavioural tests

were correlated through the Pearson correlation coefficient (PROC CORR).

Playing behaviour

The playing behaviour data showed no normal distribution. All data were log10 (X + 1)

transformed to obtain normality of residuals of the linear mixed models used (PROC

MIXED). The chosen model included the fixed effects observer (1-4), farm (farm 1, farm 2

and farm 3), gender (female, male), points of testing (first fattening phase, final fattening)

nested in farm, day (1, 2) nested in farm together with a random effect of each individual pig

nested in farm and gender and was applied to analyse the data of the total duration of playing

behaviour (s/h) and total duration of locomotor respectively social play (s/h). The same model

with the additional fixed effect location nested in farm was used to compare the total duration

of playing behaviour (s/h) between the inside and outside area of farms 2 and 3; for this, a

dataset was used that included only these two farms. As there were too few observations in

some play categories to apply statistical models, the differences between the farms within the

individual play categories were analysed descriptively using the Kruskal-Wallis test.

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The tail respectively ear postures were noted as binomial data (0 = respective tail or ear

posture was not shown; 1 = respective tail or ear posture was shown) and were analysed using

the GLIMMIX procedure with a binomial distribution (link-function = logit). Fixed effects

were added to the model in a stepwise manner. The model for the data of the curled-up tails,

hanging tails and ears directed forwards included the fixed effects farm (1-3), points of testing

(beginning respectively end of fattening) nested in farm, gender (female, male) and a random

effect of each individual pig nested in farm. The model for the data of the raised tails,

wagging tails and laterally directed ears included the fixed effects of farm (1-3), gender

(female, male) and a random effect of each individual pig nested in farm. Statistical

significance was determined at p<0.05 and the significance of differences in the least square

means was adjusted with the Bonferroni-correction. Due to rare occurrences, statistical

models could not be used for the data of the tucked-under tails, ears directed backwards and

ears mixed and therefore these results are not shown.

Influence of the pigs’ positive affective state on behavioural and physiological parameters

The partial least squares structural equation modelling method (PLS-SEM) was applied to

analyse the most appropriate parameters to estimate the latent variable of the fattening pigs’

primarily positive affective state and to evaluate the latent structures in between the

behavioural and physiological parameters.

General scheme of a structural equation model (SEM)

A SEM includes two types of latent variables which indicate the relationships between them.

There are not directly measurable latent variables and latent measurement variables, which

enable an estimation of the former latent variables. A structural model which consists of

endogenous respectively exogenous latent variables and at least two measurement models

(latent measurement variables and their self-characterising indicators) depict a SEM. The

relationships (path coefficients) between the endogenous respectively exogenous latent

variables are represented by connected arrows to each other. Endogenous (dependant) latent

variables can be affected by other latent variables, irrelevant whether they are endogenous or

exogenous, though exogenous (independent) latent variables cannot be influenced by other

latent variables. Accordingly, the coefficient of determination (R²), which indicates to which

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extent the latent variable is explained by other latent variables, is exclusively analysed for

endogenous latent variables.

Hierarchical Component Models (HCM)

The SEM of the present thesis needed an operationalisation at a higher abstraction level so a

hierarchical component model (HCM) with two levels of abstraction was conducted to

analyse the influence of the pigs’ positive affective state on different behavioural and

physiological parameters. The higher-order component (HOC) which depicts the more

abstract level and the lower-order components (LOC) which include the sub-dimensions of

the higher component form the two levels of abstraction of a HCM. In the present thesis, the

pig’s affective state represented the HOC and the different behavioural and physiological

parameters illustrated the LOC. A reflective-reflective HCM was used which included a

reflective relationship between the HOC and LOC whereby all constructs of LOC were

indicated by reflective measurement models. A reflective measurement model implies that the

indicators represent the underlying construct and that the causality of the construct is directed

to the indicators. In order to form the HOC measurement model, all indicators of the LOC

were used repeatedly to the HOC (Hair et al., 2017).

Assessment of the SEM

The evaluation involves a two-stage process whereby firstly the measurement models are

proven, followed by the evaluation of the structural model. Quality criteria of the

measurement models involve the internal consistency reliability (composite reliability) and

convergent validity (indicator reliability and average variance extracted (AVE)). Regarding

the consistency reliability, the composite reliability takes different loadings of indicators into

account and illustrates values between 0 and 1. In exploratory research studies, composite

reliability should assume values between 0.6 and 0.7. The indicator reliability evaluates how

sufficient a latent variable is estimated by an indicator with regard to the convergent validity.

AVE depicts the extent to which a latent construct explains the variance of its indicators.

AVE should achieve values above or equal to 0.5.

Important quality criteria of the structural model include the examination of the coefficients of

determination (R²) and the relevance and statistical significance of path coefficients. The path

coefficients characterise the relationships between the constructs in the structural model and

comply with the standardised regression coefficients in the regression analysis. Path

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coefficients verify or refute the pre-hypothesised relationships between the constructs in the

model by showing values between -1 and 1. For this, the sign and magnitude of the path

coefficients have to be considered (Henseler et al., 2009). An estimated path coefficient near

to +1 indicates a strong, positive relationship between examined constructs (and vice versa for

negative values), which is typically statistically significant. The weaker the relationship, the

closer the estimated path coefficient is to 0. Very low values close to 0 are generally not

statistically significant (Hair et al., 2017) whereby the statistical significance is proven by the

bootstrapping method. The coefficients of determination (R²) illustrate the proportion of the

variance of an endogenous construct that is explained by all precursor constructs

corresponding to the endogenous construct. The construct is explained all the better, the

higher the R²-values are (Hair et al., 2017). R2-values of 0.25, 0.50 and 0.75 are assessed as

weak, moderate and substantial, respectively (Henseler et al., 2009; Hair et al., 2011).

145

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DANKSAGUNG

Mein besonderer Dank gilt meinem Doktorvater Herrn Prof. Dr. Joachim Krieter für die

Überlassung des interessanten Promotionsthemas, die gute wissenschaftliche Betreuung und

die Möglichkeiten meine Ergebnisse auf nationalen sowie internationalen Konferenzen

präsentieren zu können.

Bei Frau Prof. Dr. Nicole Kemper möchte ich mich herzlich für die Übernahme des

Koreferates bedanken.

Ein besonderer Dank für die Entwicklung des wunderbaren Projektes „FeelGood“ gilt Frau

Dr. Irena Czycholl. Zudem möchte ich ihr und Frau Dr. Kathrin Büttner für die motivierende

Betreuung und für das stets schnelle und sorgfältige Korrekturlesen danken.

Den Betriebsleitern der drei Betriebe danke ich für die Bereitstellung ihrer Mastschweine und

das allseits gewährte Vertrauen während der gesamten Datenaufnahme.

Für die schöne Zeit am Institut, dem einen oder anderem „Bauernball“- oder „Born for Korn“-

Besuch, gemeinsamen Grillen, unterhaltsamen Schlachthofbesuchen und gegenseitiger

Unterstützung möchte ich allen derzeitigen und insbesondere ehemaligen Kollegen danken!

Ein großes Dankeschön für eine wunderbare Zeit, jederzeit sich sehr ergänzende

Zusammenarbeit und das stets offene Ohr gilt dem anderen „FeelGoodie“ Farina, eine bessere

Partnerin hätte ich mir für diese enge Teamarbeit nicht wünschen können.

Auch meinen lieben Freunden außerhalb des Institutes möchte ich für die ständige Motivation

und Unterstützung während der gesamten Promotionszeit danken.

Ein spezieller Dank gilt meinem Freund, der mich mit seinem unermüdlichen Drang und der

Motivation „Im Auftrag der Landwirtschaft“ zu arbeiten, unterstützte und stets zu motivieren

wusste.

Mein größter Dank gilt meiner Familie. Ihr habt mich immer unterstützt, an mich geglaubt

und mir in jeglicher Form Rückhalt geboten. Ohne euch wäre ich nicht dorthin gekommen,

wo ich jetzt bin.

LEBENSLAUF

Persönliche Daten

Name Katja Lisabeth Krugmann

Geburtsdatum 05. März 1991

Geburtsort Lübeck

Beruflicher Werdegang

seit 07/2016 Wissenschaftliche Mitarbeiterin am Institut für Tierzucht und Tierhaltung der Christian-Albrechts-Universität zu Kiel in der Arbeitsgruppe von Herrn Prof. Dr. Joachim Krieter

06/2016 Master of Science Agrarwissenschaften, Christian-Albrechts-Universität zu Kiel

12/2014 Bachelor of Science Agrarwissenschaften, Christian-Albrechts-Universität zu Kiel

Ausbildung

10/2010 – 06/2016 Studium der Agrarwissenschaften an der Christian-Albrechts-

Universität zu Kiel Abschluss: Master of Science Agrarwissenschaften

09/2001 – 07/2010 Leibniz Gymnasium Bad Schwartau Abschluss: Abitur

Dissertation Krugmann

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