Indirect Genetic Effects (IGEs), also known as associative effects, are the heritable effects that an individual has on the phenotype of its social partners. Selection for IGEs has been proposed as a ...method to reduce harmful behaviours, in particular aggression, in livestock and aquaculture. The mechanisms behind IGEs, however, have rarely been studied. The objective was therefore to assess aggression in pigs which were divergently selected for IGEs on growth (IGEg). In a one generation selection experiment, we studied 480 offspring of pigs (Sus scrofa) that were selected for relatively high or low IGEg and housed in homogeneous IGEg groups in either barren or enriched environments. Skin lesion scores, a proxy measure of aggression, and aggressive behaviours were recorded. The two distinct IGEg groups did not differ in number of skin lesions, or in amount of reciprocal fighting, both under stable social conditions and in confrontation with unfamiliar pigs in a 24 h regrouping test. Pigs selected for a positive effect on the growth of their group members, however, performed less non-reciprocal biting and showed considerably less aggression at reunion with familiar group members after they had been separated during a 24 h regrouping test. The enriched environment was associated with more skin lesions but less non-reciprocal biting under stable social conditions. Changes in aggression between pigs selected for IGEg were not influenced by G×E interactions with regard to the level of environmental enrichment. It is likely that selection on IGEg targets a behavioural strategy, rather than a single behavioural trait such as aggressiveness.
Affiliative behaviour may have an essential role in many behavioural processes. Gently nosing between group members occurs in almost all social behavioural processes of pigs (Sus scrofa), but the ...reasons for its performance are unclear. We examined whether nosing between pigs was related to dominance relationships or harmful behaviours such as manipulation of the tail using 80 crossbred pigs. Both males and females, housed in straw pens, were studied at 8 weeks of age (10 pigs/pen). Dominance ranks were determined by a feed competition test. The behaviour of 64 focal pigs was observed for 2 h per pig in total. Pigs nosed their pen mates on average 36 ± 3 times within 2 h, and nosing behaviour mainly consisted of nose-to-nose contact, nosing the head and nosing the body, rather than nosing the ear, groin, tail or ano-genital region. These gentle pig-directed nosing behaviours, i.e. gently touching another individual with the snout, was here defined as social nosing. Dominance relationships did not influence the amount of nosing given or received. Social nosing was largely unrelated to harmful behaviour. Nosing the tail correlated with tail biting (rs = 0.37), but only 0.3 percent of social nosing was followed by this behaviour. Pigs which delivered much nosing did not receive less aggression, and nor did they receive a heightened amount of nosing in return. We suggest that pigs may nose each other for social recognition, as affiliative behaviour, to gain olfactory signals, or to satisfy an intrinsic need to nose. In conclusion, social nosing in pigs was largely unrelated to harmful behaviours, was not related to dominance relationships and should remain largely unaffected by efforts to minimise harmful behaviours in farming systems
Indirect genetic effects (IGEs) are heritable effects of an individual on phenotypic values of others, and may result from social interactions. We determined the behavioural consequences of selection ...for IGEs for growth (IGEg) in pigs in a G × E treatment design. Pigs (
n
= 480) were selected for high versus low IGEg with a contrast of 14 g average daily gain and were housed in either barren or straw-enriched pens (
n
= 80). High IGEg pigs showed from 8 to 23 weeks age 40 % less aggressive biting (
P
= 0.006), 27 % less ear biting (
P
= 0.03), and 40 % less biting on enrichment material (
P
= 0.005). High IGEg pigs had a lower tail damage score (high 2.0; low 2.2;
P
= 0.004), and consumed 30 % less jute sacks (
P
= 0.002). Selection on high IGEg reduced biting behaviours additive to the, generally much larger, effects of straw-bedding (
P
< 0.01), with no G × E interactions. These results show opportunities to reduce harmful biting behaviours in pigs.
Social conflict is mostly studied in relation to aggression. A more integral approach, including aggressive and affiliative behaviour as well as physiology, may however give a better understanding of ...the animals' experience during social conflict. The experience of social conflict may also be reflected in the spatial distribution between conspecifics. The objective was to assess the relationship between behaviour, physiology, and spatial integration in pigs (Sus scrofa) during social conflict. Hereto, 64 groups of pigs (9 wk of age) were studied in a 24 h regrouping test whereby pairs of familiar pigs were grouped with 2 unfamiliar pairs, in either barren or straw-enriched housing. Data on aggressive and affiliative behaviour, skin lesions, body weight, and haptoglobin could be summarized into three principal component analysis factors. These three factors were analysed in relation to spatial integration, i.e. inter-individual distances and lying in body contact. Pigs stayed up to 24 h after encounter in closer proximity to the familiar pig than to unfamiliar pigs. Pigs with a high factor 1 score were more inactive, gave little social nosing, had many skin lesions and a high body weight. They tended to space further away from the familiar pig (b = 1.9 cm; P = 0.08) and unfamiliar ones (b = 0.7 cm; P = 0.05). Pigs that were involved in much aggression (factor 2), and that had a strong increase in haptoglobin (factor 3), tended to be relatively most far away from unfamiliar pigs (b = 0.03 times further; P = 0.08). Results on lying in body contact were coherent with results on distances. Pigs in enriched housing spaced further apart than pigs in barren housing (P<0.001). The combined analysis of measures revealed animals that may either promote or slow down group cohesion, which may not have become clear from single parameters. This emphasizes the importance of an integral approach to social conflict.
Animal welfare in pig production is frequently a topic of debate and is sensitive in nature. This debate is partly due to differences in values, forms, convictions, interests and knowledge among the ...stakeholders that constitute differences among their frames of reference with respect to pigs and their welfare. Differences in frames of reference by stakeholder groups are studied widely, but not specifically with respect to animal behaviour or welfare. We explored this phenomenon using a qualitative behaviour assessment (QBA). Participating stakeholders were classified into two expert groups consisting of pig farmers (N = 11) and animal scientists (N = 18) and a lay-group consisting of urban citizens (N = 15). The stakeholders were asked to observe the behaviour of a specific pig in each of the nine videos and to assign a score for each video using 21 predefined terms describing the mood, such as ‘happy’ or ‘irritated’. They were asked to complete two additional questionnaires to obtain information on their frames of reference. Results from the QBA showed that the pig farmers observed the behaviour of pigs more positively than the urban citizens and the animal scientists. This was evident from the consistently higher scores on the positive terms to assess pig behaviour. The questionnaires revealed that the farmers had a different frames of reference regarding pigs and different understanding of welfare, which might explain the differences in assessment. In a follow-up stakeholder workshop, which focussed on differences in observation, QBA showed to be an effective tool to stimulate mutual learning among stakeholders, which is necessary to find shared solutions.
Social interactions between individuals living in a group can have both positive and negative effects on welfare, productivity, and health of these individuals. Negative effects of social ...interactions in livestock are easier to observe than positive effects. For example, laying hens may develop feather pecking, which can cause mortality due to cannibalism, and pigs may develop tail biting or excessive aggression. Several studies have shown that social interactions affect the genetic variation in a trait. Genetic improvement of socially-affected traits, however, has proven to be difficult until relatively recently. The use of classical selection methods, like individual selection, may result in selection responses opposite to expected, because these methods neglect the effect of an individual on its group mates (social genetic effects). It has become clear that improvement of socially-affected traits requires selection methods that take into account not only the direct effect of an individual on its own phenotype but also the social genetic effects, also known as indirect genetic effects, of an individual on the phenotypes of its group mates. Here, we review the theoretical and empirical work on social genetic effects, with a focus on livestock. First, we present the theory of social genetic effects. Subsequently, we evaluate the evidence for social genetic effects in livestock and other species, by reviewing estimates of genetic parameters for direct and social genetic effects. Then we describe the results of different selection experiments. Finally, we discuss issues concerning the implementation of social genetic effects in livestock breeding programs. This review demonstrates that selection for socially-affected traits, using methods that target both the direct and social genetic effects, is a promising, but sometimes difficult to use in practice, tool to simultaneously improve production and welfare in livestock.
Pigs may affect each other's health, welfare and productivity through their behaviour. The effect of a pig on the growth rate of its pen mates is partly heritable and is referred to as its social ...genetic effect. Social genetic effects, also known as indirect genetic effects, have been found in a number of livestock breeds, in natural and laboratory populations, and in plant breeding and forestry, and have become an important research topic in recent years. In pigs, social genetic effects are hypothesized to be related to behaviour. The mechanism behind social genetic effects for growth, as well as the relationship between behaviours and growth itself, is largely unknown. To gain insight in the mechanism behind social genetic effects, we investigated the relationship between behaviours and growth rate in pigs. On a commercial pig farm, 398 finishing pigs in 50 pens (eight pigs/pen) were observed at 12 weeks of age using 2-min instantaneous scan sampling for 6 h during daytime. For 324 observed pigs, growth rate during the finishing period was known. The relationship between behaviours and growth rate during the finishing period was analysed with behaviour as explanatory variable in a mixed model. Results show that time spent giving behaviours, like oral manipulation, social nosing, aggression and belly nosing, was not related to own growth rate. Receiving behaviours, however, did relate to growth. Pigs that received more oral manipulation, observed as tail biting, ear biting and paw biting, grew less well (P <0.05). Growth rate was 43 (± 17) g/d lower in pigs that received oral manipulation during more than 2% of the observations as compared to pigs that did not receive oral manipulation. Pigs that received social nosing, a gentle touch or sniff at any part of the body, had a higher growth rate (P <0.05): growth rate differed 29 (± 17) g/d between pigs that received social nosing during more than 2% of observations as compared to not receiving social nosing at all. Receiving aggression and belly nosing, a forceful rubbing of the belly, did not influence growth rate. In conclusion, receiving oral manipulation and social nosing related to growth rate. This suggests that pigs selected for positive social genetic effects for growth may potentially show behavioural changes. Effects of selection for social genetic effects on behaviour and growth will be studied in future research.
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•Tail postures are increasingly used as indicator for aspects of pig welfare.•We reviewed the literature on tail postures and tail motions of pigs.•Pig tails were observed in positive ...and negative situations and emotional states.•We mapped tail postures and motions on the valence and arousal dimensions.•Ethograms and recommendations are given for future studies.
Animals’ tail posture and motion play an important role in communication, amongst others. In domestic pigs, the debate around tail docking and tail biting has made the tail an important research topic, and tail-related behaviour is increasingly proposed as a welfare indicator. While the focus is mostly on tail biting, the broader meaning of the tail and the information it provides tends to be forgotten. The aim of this review is to give an overview of the current knowledge on tail postures and motions in pigs (Suidae) and to provide methodological recommendations for future research. The literature describes the various tail postures and tail motions of pigs during behaviours such as locomotion, feeding, and social interactions. Moreover, research has led to an increased understanding of how tail postures and motions relate to the animal’s experiences and emotions. Overall, the tail can provide useful information about the pig’s physical and emotional experience at that moment. We propose a detailed ethogram including both tail postures and tail motions and give recommendations for observation methods. In order to guide further research, we allocated the tail postures to the four quadrants of the circumplex model of affect, which describes emotional state on a valence and arousal axes. Although exceptions occur in each quadrant (i.e. valence-arousal combination), in general, a curled tail (in domestic pigs) can be allocated to the quadrant of positive valence and high arousal, whereas a relaxed hanging but loosely wagging tail can be allocated to the quadrant of positive valence and low arousal. The tucked motionless tail can be allocated in the quadrant of negative valence and low arousal when (semi-) chronically tucked; and in the quadrant of negative valence and high arousal when it is a sudden response to a potential threat. Given the many different situations in which the tail is hanging, caution is needed when interpreting this posture. In conclusion, there is a substantial body of literature on tail postures and motions which may aid in interpreting pig tails correctly in terms of the animal’s experience.
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