Investigations on agonistic behaviour in pigs kept under commercial farm conditions

Transcription

1 Aus dem Institut für Tierzucht und Tierhaltung der Agrar- und Ernährungswissenschaftlichen Fakultät der Christian-Albrechts-Universität zu Kiel Investigations on agonistic behaviour in pigs kept under commercial farm conditions Dissertation zur Erlangung des Doktorgrades der Agrar- und Ernährungswissenschaftlichen Fakultät der Christian-Albrechts-Universität zu Kiel vorgelegt von M.Sc. Andreas Stukenborg aus Vechta Dekanin: Prof. Dr. K. Schwarz 1. Berichterstatter: Prof. Dr. J. Krieter 2. Berichterstatter: Prof. Dr. G. Thaller Tag der mündlichen Prüfung: 7. Februar 2011 Die Dissertation wurde mit dankenswerter finanzieller Unterstützung der H. Wilhelm Schaumann Stiftung angefertigt

2

3 TABLE OF CONTENTS GENERAL INTRODUCTION... 1 CHAPTER ONE Agonistic behaviour after mixing in pigs under commercial farm conditions... 5 CHAPTER TWO Heritabilities of agonistic behavioural traits in pigs and their relationships within and between different age groups CHAPTER THREE Relationship between agonistic behaviour, growth and reproductive performance in pigs CHAPTER FOUR The use of a lesion score as an indicator for agonistic behaviour in pigs GENERAL DISCUSSION GENERAL SUMMARY ZUSAMMENFASSUNG... 83

4

5 GENERAL INTRODUCTION Agonistic behaviour is a common component of social interactions in pigs. In general, agonistic behaviour describes both aggressive and submissive manners (Langbein and Puppe, 2004). Aggression among pigs occurs during regrouping of pigs unacquainted with one another or when competition for food is provoked by food shortage or restricted feeding space (Løvendahl et al., 2005). In common pig husbandry, agonistic behaviour can especially be observed directly after mixing when the pigs fight in order to establish a clear dominance hierarchy (Ewbank, 1976). Generally, the mixing of pigs is performed in three different age classes. The first mixing time takes place directly after weaning. The second regrouping occurs after pigs are taken from rearing to the fattening unit. The third mixing time concerns breeding sows when they are kept in a group-housing pregnancy area. Aggressive encounters often result in skin injuries and can additionally cause immunosuppressive effects (Tuchscherer and Manteuffel, 2000). Arey and Edwards (1998) reported that social stress can affect the sows productivity by influencing their reproductive physiology. Therefore, involvement in agonistic interactions is associated with negative effects on animal welfare as well as on the economy of pig production. An analysis of agonistic behaviour has already been made in numerous studies. However, most of these investigations have been carried out under experimental conditions and only observed pigs of one age group. The aim of the present study was to examine the agonistic behaviour of pigs over time with the aid of several behavioural traits under commercial farm conditions. Agonistic interactions were observed by video equipment at the three common mixing times in pig husbandry. The behavioural data of the three times were analysed in order to provide hints concerning the ontogenesis of agonistic behaviour. With regard to the persistence of agonistic interactions after regrouping, Puppe et al. (1997) showed that agonistic behaviour rose continuously over several days after weaning, while other authors have observed severe fights only in the first three (Friend et al., 1983) or first 24 hours (Meese and Ewbank, 1973). Due to these inconsistent findings, the aim of Chapter One was to describe fighting behaviour over a 48-hour observation time and to expose essential observation periods in which most of the fights occur. In addition, different behavioural traits and a dominance index were presented in order to illustrate the fighting level of the pigs. 1

6 According to D Eath et al. (2009), aggressive behaviour is moderately heritable and could be reduced by genetic selection. However, only a few studies have even estimated the heritabilities of agonistic behaviour after mixing pigs. For weaned piglets no heritabilities have been estimated until now. Furthermore, with relation to possible behavioural observation times for breeding it is still unexplained as to whether an aggressive female piglet becomes an aggressive growing pig and sow. Therefore, the objective of Chapter Two was to calculate correlations between the behavioural traits of different age groups. Additionally, the heritability of different agonistic behavioural traits was estimated for all three age groups. There is also a lack of investigations in the literature which deal with the relationships between agonistic behaviour and current performance traits in pig breeding. Thus, it is still uncertain as to whether an increased consideration of agonistic behaviour in pig breeding would have negative effects on common performance traits. For this reason, Chapter Three presents correlations estimated between agonistic behavioural traits, and growth rate and backfat depth, respectively. Also relationships were analysed between reproductive performance and the agonistic behavioural traits of gilts. A lesion score has frequently been used as a proxy indicator of post-mixing aggression (Turner et al., 2006). However, the scores mostly include an exact count of the scratches and are therefore not feasible for application under common breeding farm conditions. An easy and rapid lesion score approach is presented in Chapter Four. For this, correlations were estimated between the applied lesion score and agonistic behavioural traits in order to examine whether the lesion score could be an indicator for agonistic behaviour in pigs. References Arey, D.S., Edwards, S.A., Factors influencing aggression between sows after mixing and the consequences for welfare and production. Livestock Production Science 56, D'Eath, R.B., Roehe, R., Turner, S.P., Ison, S.H., Farish, M., Jack, M.C., Lawrence, A.B., Genetics of animal temperament: aggressive behaviour at mixing is genetically associated with the response to handling in pigs. Animal 3,

7 Ewbank, R., Social hierarchy in suckling and fattening pigs: A review. Livestock Production Science 3, Friend, T.H., Knabe, D.A., Tanksley, T.D., Jr., Behavior and performance of pigs grouped by three different methods at weaning. Journal of Animal Science 57, Langbein, J., Puppe, B., Analysing dominance relationships by sociometric methods - a plea for a more standardised and precise approach in farm animals. Applied Animal Behaviour Science 87, Løvendahl, P., Damgaard, L.H., Nielsen, B.L., Thodberg, K., Su, G., Rydhmer, L., Aggressive behaviour of sows at mixing and maternal behaviour are heritable and genetically correlated traits. Livestock Production Science 93, Meese, G.B., Ewbank, R., The establishment and nature of the dominance hierarchy in the domesticated pig. Animal Behaviour 21, Puppe, B., Tuchscherer, M., Tuchscherer, A., The effect of housing conditions and social environment immediately after weaning on the agonistic behaviour, neutrophil/lymphocyte ratio, and plasma glucose level in pigs. Livestock Production Science 48, Tuchscherer, M., Manteuffel, G., The effect of psycho stress on the immune system. Another reason for pursuing animal welfare (Review). Archiv für Tierzucht - Archives of Animal Breeding 43, Turner, S.P., Farnworth, M.J., White, I.M.S., Brotherstone, S., Mendl, M., Knap, P., Penny, P., Lawrence, A.B., The accumulation of skin lesions and their use as a predictor of individual aggressiveness in pigs. Applied Animal Behaviour Science 96,

8 4

9 CHAPTER ONE Agonistic behaviour after mixing in pigs under commercial farm conditions Andreas Stukenborg 1, Imke Traulsen 1, Birger Puppe 2, Ulrich Presuhn 3, Joachim Krieter 1 1 Institute of Animal Breeding and Husbandry, Christian-Albrechts-University, D Kiel, Germany 2 Leibniz Institute for Farm Animal Biology (FBN), D Dummerstorf, Germany 3 farm concepts GmbH & Co. KG, D Wahlstedt, Germany Published in Applied Animal Behaviour Science, 2011, 129:

10 Abstract The aim of the study was to investigate agonistic behaviour of pigs after regrouping pigs under commercial sow farm conditions. The behavioural patterns were observed over a 48- hour period, directly after weaning (PIG-28; n = 647) and 40 days later (growing pigs, PIG- 68; n = 224). Agonistic interactions were analysed by noting the times (start and finish), the aggressor/receiver and the winner/loser of a fight. Differences in agonistic behaviour within and between the two age groups were recorded. The median number of fights per pig was 40.0 (PIG-28) and 6.5 (PIG-68) respectively and varied between 0 and 139 fights. A circadian rhythm for the number of fights per pig and hour was shown for both age groups. A dominance index (DI) was calculated to examine possible relations between the agonistic behaviour shown and the dominance of an individual pig. The DI was defined as the ratio of wins minus defeats divided by the sum of wins, defeats and stand-off outcomes. Dominant pigs (DI > 0) were engaged in more agonistic interactions, had a longer total fight time and initiated more fights (p < 0.05) than subordinate pigs. Significant correlations (p < 0.05) were found between the overall fight time and the dominance index with r = 0.35 (PIG-28) and r = 0.53 (PIG-68). Potential coherences between agonistic behaviour and the number of skin lesions were investigated with a lesion score (LS). The LS ranked from 0 to 4 and was determined at the beginning (LSstart) and at the end (LSend) of the observation period. The analyses of the LS showed significant preferences for the front third of the body (p < 0.05). However, unambiguous findings were only made concerning the older age group. Growing pigs with an increased LS after 48 hours had more fights per pig, a longer overall fight time and initiated more fights (p < 0.05) compared to pigs showing a lower or unchanged LS. In conclusion, the applied dominance index and lesion score are feasible methods to analyse fighting behaviour under commercial sow farm conditions. Potential relationships between agonistic behaviour and growth or reproductive performance should be analysed in further investigations. It might be beneficial to consider agonistic behaviour in pig breeding. In this context, the presented approaches are simple tools to measure agonistic pig behaviour. Keywords: pig, agonistic behaviour, mixing, dominance index, lesion score 6

11 1. Introduction Agonistic behaviour includes an aggressive as well as a submissive manner. In pig husbandry, such behaviour can especially be observed when unknown pigs are mixed into new groups. The level of aggressive behaviour depends on several circumstances such as differences in body weight, different space or group sizes or the degree of familiarity. It has been reported that heavier pigs in a group fight more with each other and win more fights (Rushen, 1987; Algers et al., 1990). Ewbank and Bryant (1972) figured out that a decrease in the area available per pig leads to an increase in agonistic interactions. Hoy and Bauer (2005) observed that mixing acquainted sows reduces the level of aggressive interactions in contrast to mixing unacquainted pigs. Aggressive encounters often result in skin injuries and can additionally cause immunosuppressive effects (Tuchscherer and Manteuffel, 2000). Hence, agonistic behaviour can lead to detrimental welfare and reduced weight gain (Tan et al., 1991; Stookey and Gonyou, 1994), thus affecting the economy of pig production. Behavioural observations had already been made in numerous studies, mostly dealing with the arising dominance relationships, often in correspondence with other behavioural and/or physiological features of the animals (Langbein and Puppe, 2004). However, these investigations had been carried out under experimental conditions, reflected by a small number of pigs in the pen. Furthermore, observations had been either made directly in the pen or with the aid of video recordings. These methods are labour-intensive and time-consuming. Recent studies (Løvendahl et al., 2005; Turner et al., 2008; Turner et al., 2009) have shown that aggressive behaviour after mixing is moderately heritable and could be reduced by genetic selection (D'Eath et al., 2009). Additionally, a lesion score has been frequently examined to find an association between aggressive behaviour and the accumulation of skin lesions. Hence, a skin lesion score assessed for the first 24 hours after regrouping is a heritable trait (Turner et al., 2006) and genetically correlated with aggressive behaviour (Turner et al., 2008; Turner et al., 2009). Therefore, skin lesions can be used to score the agonistic capability of a pig. By using a lesion score approach there is no need to make timeconsuming behavioural observations. Evaluation methods, for example, could be part of the routine (Turner et al., 2008). Thus, an implementation of agonistic behaviour in commercial breeding programs would be easier to handle. In contrast to previous investigations, the data collection was carried out under commercial sow farm conditions. Consequently, the findings might prove to be more beneficial concerning the practicability of breeding pigs using agonistic behavioural traits. 7

12 The aim of the present paper was to show the course of agonistic behaviour in the passage of time and to examine several behavioural traits (e.g. number of fights, fight time or initiated fights per pig) at two different times of regrouping referring to common pig breeding. Thus, essential observation periods were shown, containing most of the fights and potential age discrepancies in agonistic behaviour. In addition, a dominance index and a lesion score were calculated in order to find a relationship between differences in agonistic behaviour and differences in lesion score and dominance index, respectively. Both the dominance index and the lesion score could possibly be considered simple means to measure agonistic behaviour in pigs. 2. Materials and Methods 2.1. Animals and housing Data were collected on a closed herd sow farm of the German breeding company Hülsenberger Zuchtschweine from October 2007 to September The herd consisted of pure-bred Large-White (LW) sows and crosses between Large-White and German Landrace (LW x DL). Due to the aim of the study to observe and analyse the behaviour of breeding sows, only female piglets from pure-bred litters (LW) and crosses from LW x DL were chosen for this study. The sows had a 28-day lactation period. Every Wednesday piglets from one sow group with 36 litters on average were weaned (one-week rhythm) and moved to the rearing house where they were sorted by gender and body size. The dimensions of the rearing pens were 5.10m x 2.10m. The pens had a fully slatted floor and were separated by 60cm high, closed partitions on the ground and two rods across. An average of 29 piglets was housed in each pen. During the rearing period the piglets were fed ad libitum with a wet feeder. Water was accessible non-stop through nipple drinkers Behavioural observation Immediately after weaning four rearing pens with female breeding piglets (LW and LW x DL) were filmed for 48 hours using the HeiTel Player software program (HeiTel Digital Video GmbH, Kiel, Germany). The recording of the weaned pigs (PIG-28) started between 15:00 and 16:30 h. By exclusion of the area around the wet feeder, the entire observation area measured 3.20m x 2.10m. For the behavioural observation, ten piglets per pen were randomly chosen and individually marked on their backs. In total, the agonistic behaviour of 647 piglets 8

13 (PIG-28) with a total of 23,995 fights was recorded. A second observation was carried out 40 days after weaning (growing pigs = PIG-68). The same 40 pigs which had already been observed at weaning were re-marked, re-mixed and re-allocated to the four rearing pens. At the second mixing, a new group was created in equal shares from the four pens which were housed at weaning, i.e. one out of four from the new group and also two or three from the marked pigs were already known to each other. After mixing, the pigs were videotaped for 48 hours. The recording (PIG-68) started between 11:40 and 15:15 h. To reduce the effort involved, the second mixing procedure was only carried out 12 times when there were purebred pigs in the rearing pens. These pigs were of particular importance for further studies because of their existing pedigrees. However, due to problems with the technical supply, only 224 pigs (PIG-68) (2,024 fights) were completely observed for the entire 48 hours. The agonistic behaviour of the marked pigs was analysed with the aid of the videotapes. The growing pigs were evaluated by one person. Four observers recorded the agonistic interactions for the weaned piglets. Prior to visual assessment, the observers were trained in the definition and identification of agonistic behaviour. Characteristically distinctive fighting sequences were studied to standardise the ratings of the fights. Finally, they were tested with the same training videotape. The derived data were stored in a database. Thereby, an agonistic interaction was defined as a fight or a displacement with physical contact initiated by one individual and featuring aggressive behavioural elements followed by any form of submissive behaviour performed by the opponent (Langbein and Puppe, 2004). Agonistic behaviour was recorded when the fights took longer than one second. If there was an intervening period of more than eight seconds, a new fight was considered to have been started (Puppe, 1998). In accordance with Puppe (1998), fights were displayed in the form of bodily attacks such as head-to-head knocks and head-to-body knocks, parallel/inverse parallel pressings, bitings or physical displacements which were induced by the aggressor pig. The loser of a fight was defined as the animal showing a submissive manner, e.g. it stopped fighting, turned away from an attack, tried to flee or was displaced from the location (Tuchscherer et al., 1998; Langbein and Puppe, 2004). The times (start time and finish time), the aggressor/receiver and the winner/loser of a fight were noted for each fight in which a marked pig was involved. If there was no clear outcome, the fight was designated as a stand-off. If an agonistic interaction moved out of the observation area for more than one minute, the fight was defined as terminated and the outcome was unclear. 9

14 2.3. Dominance index A dominance index (DI) was calculated to express the strength and the dominance of the observed pigs. The index was chosen referring to Bowen and Brooks (1978), who designed an index as the ratio of wins minus defeats to all decisive fights. However, due to the high number of stand-offs for a considerable number of piglets in the present study, the DI was calculated including the fights which were classed as indecisive. In this way, the dominance of a stand-off piglet was reflected more accurately. The DI was defined as the sum of wins minus defeats to wins, defeats and stand-off outcomes. wins defeats DI = wins+ defeats+ stan doffs According to this calculation, no DI can be calculated for those pigs that were not involved in any fighting or only had uncertain fight outcomes (one for PIG-28, 15 for PIG-68). The dominance index ranked from -1 (absolute submissive) to +1 (absolute dominant). In order to plot the DI (Figure 2), values were summarised in steps of 0.1 (0 = to 0.05), except the DI from 0.9 and -0.9, respectively, which included all data from 0.85 (-0.85) to <1 (> -1) Lesion score In addition to the behavioural observations, a skin lesion score (LS) was assigned to all pigs marked immediately before starting the 48-hour observation period (LSstart). After 48 hours (PIG-68) or one week later (PIG-28), the LS was recorded again (LSend) for the majority of the observed pigs. The time differences between the first and second recordings (48 hours vs. one week) were due to management reasons (the workflow on the farm was to be disrupted as little as possible). To evaluate the skin areas mainly affected, the body was divided into three regions: front (head, neck, shoulders and front legs), middle (flanks and back) and rear (rump, hind legs and tail) (modified according to Turner et al., (2006)). The three regions were evaluated independently of each other. The LS ranked from 0 (no wounds and scratches) to 4 (many, deep wounds and scratches). The change in the LS (LSdiff) was described as the difference of LSend minus LSstart. Based on this definition the LSdiff could also be negative for pigs showing more scratches at the beginning than at the end of the observation period. In total, the LSdiff was calculated for 606 (PIG-28) and 184 (PIG-68) pigs, respectively. 10

15 2.5. Statistical analysis Data analysis was performed using the SAS statistical software package (SAS Institute Inc., 2004). The UNIVARIATE procedure in SAS (2004) was applied to test for normal distribution (Shapiro-Wilk test). Due to the non-normal distribution of all behavioural traits, including the fights per pig and hour, the medians were calculated for descriptive statistics (Proc MEANS; SAS 2004). The Wilcoxon rank-sum test (Proc NPAR1WAY; SAS 2004) was used to identify significant differences in the number of agonistic interactions per hour during daytime. Medians were compared between morning, midday and evening as well as the night and daytime results. The same test was applied to compare the medians of the behavioural parameters from animals with a DI larger or less than zero. Pigs with a DI = 0 were not considered in this test. Previous investigations had shown that these pigs did not influence the results. Furthermore, the Wilcoxon rank-sum test was used to find differences between the LS of the three body areas and to compare the medians of behavioural parameters from pigs with a positive or non-positive front LSdiff. Due to the non-normal distribution of the different behavioural traits, Spearman correlation coefficients (Proc CORR; SAS, 2004) were calculated for behavioural parameters, dominance index and the front LSdiff. 3. Results 3.1. Behavioural parameters Weaned piglets (PIG-28) A winner and a looser could be assigned to 39.1% of all the observed agonistic interactions. Most fights were rated as stand-offs (47.8%). Due to the existing space outside the observation area, the remaining outcomes (13.1%) and additionally 23.7% of the fight beginnings could not be specified. Table 1 shows the different behavioural indicators. All traits presented a wide range. One piglet had no fight at all in the first 48 hours; in contrast, one piglet had 139 agonistic interactions. The number of fights per piglet and hour is illustrated in Figure 1. The course shows significant variations during the times of day. In general the number of agonistic interactions was significantly smaller during the night (h 2-13 and h 26-37) than during the daytime (h 1, h 14-25, and h 38-48) (p < 0.05). 11

16 Table 1: Median, minimum (Min.) and maximum (Max.) of the behavioural parameters, observed for 48 hours after weaning (PIG-28) and second mixing (PIG68) PIG-28 (n = 23,995) PIG-68 (n = 2,024) Median Min. Max. Median Min. Max. Fights per pen 1) Fights per pig Fight time per pig (s) Fighting duration (s) Initiated fights per pig Fights won per pig Fights lost per pig Stand-off fights per pig ) observation area fights/pig/hour fights/piglet/hour PIG-28 (n = 23995) evening a midday b morning a evening a morning a midday b PIG-68 (n = 2024) evening a morning b midday c evening a morning b hours after mixing Figure 1: Fights per piglet and hour after the first (PIG-28) and second (PIG-68) mixings. Daytimes with different letters are significantly different (p 0.05) 12

17 Growing pigs (PIG-68) For the growing pigs, 47.1% of the agonistic interactions showed a clear result. 43.7% of the fights were observed as stand-offs and 9.2% had no outcome in the observation area. The initiator was out of sight in 17.2% of the fights. Similar to the younger pigs, the behavioural traits of these growing pigs showed a wide range of results, but the mean values were considerably lower (Table 1). In total, 13 pigs had no fights in the first 48 hours. The growing pigs fought much more during the daytime than during the night (p < 0.05) (Figure 1). No agonistic interaction was observed in hour Dominance index Weaned piglets (PIG-28) More than two thirds of the piglets had a DI of between and There was one absolutely submissive piglet (DI = -1) and nine animals had a high index of 0.6 (see Figure 2). The median DI was Number of pigs PIG-28 (n = 647) PIG-68 (n = 224) Dominance index Figure 2: Dominance index of weaned piglets (PIG-28) and growing pigs (PIG-68) Growing pigs (PIG-68) The median DI for the growing pigs was Twenty-six animals had no winner outcomes (DI = -1) in contrast to one pig which was absolutely dominant. The other dominant pigs had an index lower than Fifteen of the 224 pigs had no DI. These pigs had no fights or the fight outcomes were uncertain. 13

18 Comparison of dominant vs. submissive piglets/pigs A comparison of dominant (DI > 0) and subordinate (DI < 0) pigs showed significant differences (p < 0.05) for the major behavioural traits in both age groups (Table 2). The dominant piglets were more active than the subordinates, expressed by a higher number of fights and a longer time involved in agonistic interactions (p < 0.05). In addition, piglets with a positive DI initiated more fights (p < 0.05). Furthermore, they had considerably more wins than defeats (p < 0.05), although this was due to the definition of the index. Table 2: Comparison of median behavioural traits between dominant and submissive pigs for the two age groups (PIG-28/PIG-68) PIG-28 (n = 23,995) PIG-68 (n = 2,024) DI < 0 DI > 0 DI < 0 DI > 0 Fights per pig 37 a* 45 b 5 a 18 b Fight time per pig (s) 1817 a 3290 b 56 a 558 b Initiated fights per pig 12 a 17 b 1 a 7 b Fights won per pig 3 a 10 b 0 a 6 b Fights lost per pig 10 a 3 b 2 a 1.5 a *Within rows and within age groups (PIG-28/PIG-68) medians with different letters are significantly different (Wilcoxon rank-um test; p < 0.05) 3.3. Lesion score Weaned piglets (PIG-28) Figure 3 shows the differences in the LS for the three body areas. No positive LSdiff, equivalent to no additional wounds in the observation period, was found for almost 51% (middle) and 68% (rear) of the piglets, respectively. More than 70% of the animals had a positive LSdiff for the front body third. One piglet exhibited a difference of four units. At the second LS recording, the LS for the front body area was significantly higher than the LS for the middle and rear body area (p < 0.05). Negative LSdiff was especially shown for the rear body region (ca. 14%). Thus, these piglets had more wounds at the first than at the second LS recording. In contrast, only about 5% of the front and 7% of the middle body third had a negative LSdiff. 14

19 PIG-28 (n = 647) Number of piglets front middle rear LS difference PIG-68 (n = 224) 100 Number of pigs front middle rear LS difference Figure 3: Lesion score difference of weaned piglets (PIG-28) and growing pigs (PIG-68) for the front, middle and rear body areas Growing pigs (PIG-68) Except for the anterior third, the distribution of the LSdiff was similar to that of the younger piglets (Figure 3). A considerable number of pigs showed only a small increase in the LS. No positive LSdiff was shown for approximately 62% and 72%, respectively, with regard to the middle and rear regions. About 56% had an increased LS after mixing, regarding the front third. Moreover, the rear and middle body area had a significantly smaller LS than the front region (p < 0.05).Due to these proportions, the front third was clearly preferred. 15

20 Comparison of negative/unchanged vs. positive LSdiff The behavioural traits of piglets with new wounds were compared to animals without new scratches. Due to the predominant body area, only the front region was considered. The young pigs had an equal number of fights per piglet (Table 3). Significant differences (p < 0.05) were shown in the fight time and the number of defeats. For the older pigs only the number of defeats was not significant. Table 3: Comparison of median front lesion score difference (LSdiff) (negative/unchanged vs. positive LSdiff) for the two age groups (PIG-28/PIG-68) PIG-28 (n = 23,995) PIG-68 (n = 2,024) LSdiff 0 LSdiff > 0 LSdiff 0 LSdiff > 0 Fights per pig 39 a* 41 a 3 a 9 b Fight time per pig (s) 1915 a 2757 b 35.5 a 174 b Initiated fights per pig 14 a 14 a 1 a 2 b Fights won per pig 6 a 6 a 0 a 0 b Fights lost per pig 8 a 6 b 2 a 2 a Average DI a a -0.5 a b *Within rows and within age groups (PIG-28/PIG-68) median with different letters are significantly different (Wilcoxon rank-sum test; p < 0.05) 3.4 Correlation between dominance index, the front LSdiff and behavioural parameters Table 4 shows the correlations (Spearman correlation coefficients) between behavioural parameters, dominance index and the lesion score difference. The dominance index was correlated with all observed behavioural traits (p < 0.05). The older pig group had apparently higher correlation coefficients, especially for the fights per piglet, the fight time per piglet and the initiated fights. In contrast to the number of fights won, the lost fights for the younger piglets were negatively correlated with the DI. However, their correlation with the DI was on the same level (r = 0.64/-0.60). For the older pigs, the fights won were highly correlated with the DI (r = 0.74), whereby the DI and the fights lost showed an apparently smaller correlation (r = -0.31). With regard to the younger animals, the LSdiff was not correlated with the number of wins and the number of initiated fights. A slightly negative correlation was found between the LSdiff and the number of fights lost. No correlation was detected between the LSdiff and the number of fights lost with regard to the older pigs. Otherwise, the LSdiff was highly correlated with all other parameters. 16

21 Table 4: Correlation between the front lesion score difference (LSdiff), dominance index (DI) and behavioural parameters PIG-28 (n = 23,995) PIG-68 (n = 2,024) DI LSdiff DI LSdiff Fights per pig 0.18* 0.10* 0.47* 0.36* Fight time per pig 0.35* 0.32* 0.53* 0.42* Initiated fights per pig 0.19* * 0.29* Fights won per pig 0.64* * 0.39* Fights lost per pig -0.60* -0.13* -0.31* 0.07 DI * * *p < Discussion Previous investigations have already shown that agonistic behaviour in pigs has a wide phenotypic range (Jensen, 1982; Forkman et al., 1995; Otten et al., 1997; Puppe et al., 1997). The current data support this statement. Moreover, the results of the present paper illustrate a clear circadian rhythm in agonistic behaviour with high aggression frequencies during daytime. Age differences between weaned and growing pigs in the number of performed agonistic interactions were ascertained. Furthermore, the findings indicate that both the applied DI and the LS approach (except for the weaned piglets) could be used to make basic statements concerning the aggressiveness of pigs. Behavioural parameters A low increase in fighting activity was observed for the weaned piglets directly after mixing. The growing pigs had the highest number of fights in the first hour after regrouping. Because of the novel situation with a great number of new pen mates, it might be that the first few hours after mixing are always fight times of high frequency regardless of the time of day. However, taking the whole 48-hours observation period into account a circadian rhythm is clearly visible. This is in accordance with Hessel et al. (2006), who observed a declined rate in agonistic behaviour at night. McGlone and Newby (1994) proved a circadian pattern in activity independent of group size. In respect of further investigations, the presence of a circadian rhythm could decrease the amount of time and work effort incurred by using videotapes. Potentially, recording is only required during the daytime when the majority of fights occur. Therefore it still has to be clarified as to whether there are pigs which are also (or 17

22 only) nocturnal or if all pigs fall into this circadian pattern. Puppe et al. (1997) showed that agonistic behaviour in weaned piglets rose continuously to day 4 after weaning. While Friend et al. (1983) observed severe fights only in the first three hours after mixing but not after 24 and 48 hours. Meese and Ewbank (1973) suggested that vigorous fighting was virtually eliminated after 24 hours and the social order was fixed within 48 hours. The current time courses in the study presented here showed no considerable decrease in the fighting level over the whole 48-hour observation period. Hence, a 24-hour observation would ignore a great quantity of information. On the contrary, for an exact description of agonistic behaviour, it might be useful to observe the pigs for considerably more than 48 hours. An observation for three or even four days after weaning could be appropriate. The present study shows a considerable difference in the quantity of fights between the groups of younger (PIG-28) and older pigs (PIG-68). A possible reason for the differences in the level of aggression could be the higher degree of familiarity inside a pen of growing pigs compared to weaned piglets. Due to the mixing procedure it became obvious that one out of four pigs already knew each other after the second regrouping. In this regard, Puppe s (1998) observation covered 12-week-old pigs in the pen area and concluded that familiar pigs were engaged in fewer agonistic interactions than unfamiliar pigs. Jensen and Yngvesson (1998) found no significant difference in the fighting behaviour between unknown and pre-exposure pigs. In their opinion, it is difficult to inhibit overt fighting between newly mixed pigs through pre-exposure. However, concerning the high agonistic level of the younger piglets in the present study, various authors have indicated that socialising pigs before weaning subsequently leads to a restricted level of fighting (Weary et al., 1999; Pitts et al., 2000; Hessel et al., 2006; Parratt et al., 2006). Such practice would reduce the number of stressors and improve the welfare of weaned piglets, which are also influenced by a new environment and diet and the separation from the sow (D'Eath, 2005). Nevertheless, pre-weaning mixing times or even weaning without separating the litters has yet been not implemented in common pig husbandry. Currently, pigs are sorted by sex as in the present study, which also seems to have a decreasing effect on agonistic behaviour (Colson et al., 2006). There were also differences between the two age groups with regard to their space allowance. Pigs (PIG-68) with a lower space allowance (kg/m 2 ) had a clearly lower aggression level overall compared with piglets with more space allowance (PIG-28). Based on a live weight of 28 kg for the older pigs (PIG-68), the space allowance was approximately 76 kg/m 2 with about 2.7 pigs per m 2. This stocking density may lead to restricted movement and social behaviour, which in turn induces fewer agonistic interactions. Meunier-Salaun et al. (1987) described that 18

23 crowding induces a breakdown in communications and pigs adopt a social avoidance strategy, preventing aggression escalation. Whereas, according to Ewbank and Bryant (1972), decreasing the area available per pig seems to increase the number of agonistic interactions. Dominance index The distribution and the median value of about zero with regard to the DI from the young piglets (PIG-28) indicates that there was a uniform ratio between subordinates and dominants in the pen. In contrast, after the second mixing, a median value of indicated that most of the growing pigs had a negative DI. These various allocations could be an indication of a changing dominance hierarchy among the animals over time. Presumably, there were only a few highly dominant growing pigs in the pen. Since nearly two thirds of the pigs were unmarked, the majority of the few dominant animals belonged to this group. A marking of all pigs in the pen would have illustrated a more precise dominance hierarchy. Based on the fact that the analysis was carried out in normal rearing pens, a marking of all 30 pigs in the pen was not possible due to the considerable time requirement and the decreasing overview. However, Table 4 shows a considerable number of correlations between the DI and the observed behavioural traits. Furthermore, clearly significant differences in the behavioural parameters were shown between the dominant and subordinate pigs, although using the least possible distinction (DI > 0 or DI < 0). These significant differences showed that the animals can be divided into more or less active fractions with the aid of a dominance index, regarding their agonistic behaviour. Lesion score According to McGlone (1985), the lesion score clearly shows high stress for the front body third in contrast to the middle and especially to the posterior third. In the present study, the younger piglets (PIG-28) had a higher front LSdiff than older pigs (PIG-68). This reflected the higher involvement in agonistic interactions of the young piglets. Associated with these findings, an investigation of the rear and of the middle lesion score seemed to be rather insignificant in relation to agonistic behaviour. Significant correlations were found between the LSdiff and the behavioural parameters for both age groups. However concerning the weaned piglets, the correlations were only small and only significant for three out of five behavioural traits. Thus, a general connection between these parameters and the LS could not be demonstrated. For the growing pigs, all behavioural parameters, except the number of fights lost, were significantly correlated with 19

24 the LSdiff. In addition, the correlation coefficients were higher compared to the younger age group (Table 4). Relationships between the LSdiff and the behavioural parameters were also shown by the comparison of the positive and non-positive LSdiff groups (Table 3). These findings confirmed the results of Turner et al. (2006), who calculated a positive correlation between the front LS and the proportion of time spent in reciprocal fighting for growing pigs. The weaned piglets fought much more than the growing pigs but apparently their interactions were not as intensive, so a fight did not always end in injury. In this respect, Donaldson et al. (2002) suggested that social play behaviour could also occur during serious aggression. Thus, the LS approach presented allowed no clear indication of agonistic interactions in weaned piglets. In contrast, the growing pigs showed a more obvious aggressiveness. Therefore, the agonistic interaction mostly ends in injury, which means that a greater number of fights also results in a higher LS. According to this, the LS method can be used as a means to estimate agonistic behaviour in growing pigs. It should be mentioned that there are references indicating that a body weight asymmetry within a pen is positively correlated with the number of scratches (Olesen et al., 1996; Turner et al., 2006; Li and Johnston, 2007). However, the statements concerning the relation between behavioural traits and pig live-weight are not consistent. D Eath (2002) reported that heavier pigs had an overall longer fight time, initiated more fights and won more often than lighter pigs. In contrast, Turner et al. (2006) found no correlation between body weight and fight time. The overall level of agonistic interactions seemed to be lower in pens with obvious differences in body weight, whereas heavier pigs fought more among themselves resulting in a high number of body lesions (Rushen, 1987; Andersen et al., 2000). However, because of the difficulties of implementing the weighing procedure in the operation flow of a sow farm, live weight was not recorded. This fact makes clear that data recording under common conditions is often associated with undesirable restrictions. 5. Conclusion In order to assess an exact description of the agonistic potential of pigs, it might be useful to observe agonistic behaviour for more than 48 hours after mixing. It may be sufficient to observe the animals only in the daytime, when the majority of fights occur. Furthermore, pigs can be divided into more or less aggressive fractions with the aid of a dominance index and the lesion score approach is a relatively easy and simple means to estimate agonistic behaviour in growing pigs. In general, the present paper reveals that it is possible to analyse 20

25 agonistic behaviour under commercial farm conditions. As such, the applied methods could be incorporated into further investigations to measure and estimate agonistic interactions. This in turn would finally help to improve the animals welfare. References Algers, B., Jensen, P., Steinwall, L., Behaviour and weight changes at weaning and regrouping of pigs in relation to teat quality. Applied Animal Behaviour Science 26, Andersen, I.L., Andenæs, H., Bøe, K.E., Jensen, P., Bakken, M., The effects of weight asymmetry and resource distribution on aggression in groups of unacquainted pigs. Applied Animal Behaviour Science 68, Bowen, D.W., Brooks, R.J., Social organization of confined male collared lemmings (Dicrostonyx groenlandicus Traill). Animal Behaviour 26, Colson, V., Orgeur, P., Courboulay, V., Dantec, S., Foury, A., Mormède, P., Grouping piglets by sex at weaning reduces aggressive behaviour. Applied Animal Behaviour Science 97, D'Eath, R.B., Individual aggressiveness measured in a resident-intruder test predicts the persistence of aggressive behaviour and weight gain of young pigs after mixing. Applied Animal Behaviour Science 77, D'Eath, R.B., Socialising piglets before weaning improves social hierarchy formation when pigs are mixed post-weaning. Applied Animal Behaviour Science 93, D'Eath, R.B., Roehe, R., Turner, S.P., Ison, S.H., Farish, M., Jack, M.C., Lawrence, A.B., Genetics of animal temperament: aggressive behaviour at mixing is genetically associated with the response to handling in pigs. Animal 3, Donaldson, T.M., Newberry, R.C., Špinka, M., Cloutier, S., Effects of early play experience on play behaviour of piglets after weaning. Applied Animal Behaviour Science 79, Ewbank, R., Bryant, M.J., Aggressive behaviour amongst groups of domesticated pigs kept at various stocking rates. Animal Behaviour 20, Forkman, B., Furuhaug, I.L., Jensen, P., Personality, coping patterns and aggression in piglets. Applied Animal Behaviour Science 45,

26 Friend, T.H., Knabe, D.A., Tanksley, T.D., Jr., Behavior and performance of pigs grouped by three different methods at weaning. Journal of Animal Science 57, Hessel, E.F., Reiners, K., Van den Weghe, H.F.A., Socializing piglets before weaning: Effects on behavior of lactating sows, pre- and postweaning behavior, and performance of piglets. Journal of Animal Science 84, Hoy, S., Bauer, J., Dominance relationships between sows dependent on the time interval between separation and reunion. Applied Animal Behaviour Science 90, Jensen, P., An analysis of agonistic interaction patterns in group-housed dry sows - Aggression regulation through an avoidance order. Appl. Anim. Ethol. 9, Jensen, P., Yngvesson, J., Aggression between unacquainted pigs - sequential assessment and effects of familiarity and weight. Applied Animal Behaviour Science 58, Langbein, J., Puppe, B., Analysing dominance relationships by sociometric methods - a plea for a more standardised and precise approach in farm animals. Applied Animal Behaviour Science 87, Li, Y.Z., Johnston, L.J., Effects of familiarity and weight variation on aggression among grow-finish pigs following regrouping. Journal of Animal Science 85 (Suppl. 2), 49. Løvendahl, P., Damgaard, L.H., Nielsen, B.L., Thodberg, K., Su, G., Rydhmer, L., Aggressive behaviour of sows at mixing and maternal behaviour are heritable and genetically correlated traits. Livestock Production Science 93, McGlone, J.J., A quantitative ethogram of aggressive and submissive behaviors in recently regrouped pigs. Journal of Animal Science 61, McGlone, J.J., Newby, B.E., Space requirements for finishing pigs in confinement: behavior and performance while group size and space vary. Applied Animal Behaviour Science 39, Meese, G.B., Ewbank, R., The establishment and nature of the dominance hierarchy in the domesticated pig. Animal Behaviour 21, Meunier-Salaun, M.C., Vantrimponte, M.N., Raab, A., Dantzer, R., Effect of floor area restriction upon performance, behavior and physiology of growing-finishing pigs. Journal of Animal Science 64,

27 Olesen, L.S., Nygaard, C.M., Friend, T.H., Bushong, D., Knabe, D.A., Vestergaard, K.S., Vaughan, R.K., Effect of partitioning pens on aggressive behavior of pigs regrouped at weaning. Applied Animal Behaviour Science 46, Otten, W., Puppe, B., Stabenow, B., Kanitz, E., Schön, P.C., Brüssow, K.P., Nürnberg, G., Agonistic interactions and physiological reactions of top- and bottom-ranking pigs confronted with a familiar and an unfamiliar group: Preliminary results. Applied Animal Behaviour Science 55, Parratt, C.A., Chapman, K.J., Turner, C., Jones, P.H., Mendl, M.T., Miller, B.G., The fighting behaviour of piglets mixed before and after weaning in the presence or absence of a sow. Applied Animal Behaviour Science 101, Pitts, A.D., Weary, D.M., Pajor, E.A., Fraser, D., Mixing at young ages reduces fighting in unacquainted domestic pigs. Applied Animal Behaviour Science 68, Puppe, B., Effects of familiarity and relatedness on agonistic pair relationships in newly mixed domestic pigs. Applied Animal Behaviour Science 58, Puppe, B., Tuchscherer, M., Tuchscherer, A., The effect of housing conditions and social environment immediately after weaning on the agonistic behaviour, neutrophil/lymphocyte ratio, and plasma glucose level in pigs. Livestock Production Science 48, Rushen, J., A difference in weight reduces fighting when unacquainted newly weaned pigs first meet. Canadian Journal of Animal Science 67, SAS Institute Inc., SAS/STAT User's guide, Version 9.1. Stookey, J.M., Gonyou, H.W., The effects of regrouping on behavioral and production parameters in finishing swine. Journal of Animal Science 72, Tan, S.S.L., Shackleton, D.M., Beames, R.M., The effect of mixing unfamiliar individuals on the growth and production of finishing pigs. Animal Production 52, Tuchscherer, M., Manteuffel, G., The effect of psycho stress on the immune system. Another reason for pursuing animal welfare (Review). Archiv für Tierzucht - Archives of Animal Breeding 43, Tuchscherer, M., Puppe, B., Tuchscherer, A., Kanitz, E., Effects of social status after mixing on immune, metabolic, and endocrine responses in pigs. Physiology & Behavior 64,

28 Turner, S.P., Farnworth, M.J., White, I.M.S., Brotherstone, S., Mendl, M., Knap, P., Penny, P., Lawrence, A.B., The accumulation of skin lesions and their use as a predictor of individual aggressiveness in pigs. Applied Animal Behaviour Science 96, Turner, S.P., Roehe, R., D'Eath, R.B., Ison, S.H., Farish, M., Jack, M.C., Lundeheim, N., Rydhmer, L., Lawrence, A.B., Genetic validation of postmixing skin injuries in pigs as an indicator of aggressiveness and the relationship with injuries under more stable social conditions. Journal of Animal Science 87, Turner, S.P., Roehe, R., Mekkawy, W., Farnworth, M.J., Knap, P.W., Lawrence, A.B., Bayesian analysis of genetic associations of skin lesions and behavioural traits to identify genetic components of individual aggressiveness in pigs. Behavior Genetics 38, Weary, D.M., Pajor, E.A., Bonenfant, M., Ross, S.K., Fraser, D., Kramer, D.L., Alternative housing for sows and litters: 2. Effects of a communal piglet area on preand post-weaning behaviour and performance. Applied Animal Behaviour Science 65,

29 CHAPTER TWO Heritabilities of agonistic behavioural traits in pigs and their relationships within and between different age groups Andreas Stukenborg 1, Imke Traulsen 1 ; Eckhard Stamer 2, Birger Puppe 3, Ulrich Presuhn 4, Joachim Krieter 1 1 Institute of Animal Breeding and Husbandry, Christian-Albrechts-University, D Kiel, Germany 2 TiDa Tier und Daten GmbH, D Westensee/Brux, Germany 3 Leibniz Institute for Farm Animal Biology (FBN), D Dummerstorf, Germany 4 farm concepts GmbH & Co. KG, D Wahlstedt, Germany 25

30 Abstract The aim of the present study was to estimate heritabilities for different agonistic behavioural traits after mixing pigs of three age classes and to compare the agonistic behaviour between the age groups. The behavioural patterns were observed over a 48-hour period, directly after weaning (PIG-28; n = 884), 40 days later (growing pigs, PIG-68; n = 351) and immediately after mixing gilts (GILTS; n = 389). Agonistic interactions were analysed by noting the times (start and finish), the aggressor/receiver and the winner/loser of a fight. Starting from this, the number and the time involved were calculated for ten agonistic behavioural traits. Intermediate heritabilities were estimated for growing pigs, with the highest heritability for the number of won fights (h 2 = 0.37). In comparison, the heritabilities for weaned piglets were at a lower level with the highest heritability for the duration spent in initiated fights (h 2 = 0.20). Concerning gilts, substantial heritabilities were only found for the number of received aggressions (h 2 = 0.42), the time spent in received aggressions (h 2 = 0.15), the number of lost fights (h 2 = 0.13) and the time spent in lost fights (h 2 = 0.09). Within an age group, the number of initiated fights was always more highly correlated with the number of won fights than with the number of lost fights indicating that pigs which initiated a fight more often also won fights more often. Moderate correlations were found between the behavioural traits from growing pigs and gilts, while relationships between the weaned piglets and older age groups were only small. In conclusion, the results indicate that more aggressive growing pigs tended to also be more aggressive sows. Additionally, the agonistic behaviour from weaned piglets cannot be compared with other age groups since the agonistic behaviour of weaned piglets is probably related to playfulness while older pigs seem to establish a new dominance hierarchy. Keywords: pig, agonistic behaviour, heritability, correlation, age groups 26