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Title: Understanding the phenotype of aggressiveness
Author: Clark, C. C. A.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2007
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Consistency of aggressiveness within and between situations was examined using a repeated social challenge test (Resident Intruder Test) at various key stages during the lifetime of male and female growing (meat) pigs and a subset of female breeding pigs. Behaviour during mixing at weaning and as gilts was examined and information was collected about the way in which these animals behaved in a social context, including measures related to, but not directly correlated with aggression, such as social status. The effects of age/maturity and experience were also considered. To understand how aggression might integrate within personality the various social measures were compared with cortisol (as a physiological indicator of stress) an a challenging situation unrelated to social confrontation; maternal behaviour was chosen as it is commercially relevant and has important implications for the welfare of gilts and piglets. Pigs were consistent in their responses to the RIT, but there were differences between sexes. Aggressiveness was consistent over a long period of time in female pigs, even with a gap of 90 days between tests and the onset of puberty. Male pigs showed an unexpectedly high level of mounting behaviour from a young age, which increased with maturity. Experience of the RIT improved consistency of responses and age at first testing affected both the speed of attacking and occurrence of attacks; those pigs experiencing the test when younger were more likely to and quicker to attach. RIT aggressiveness was however, not predictive of subsequent aggressiveness at mixing. As with the RIT, there were clear sex-differences observed during mixing at weaning with males being more aggressive, more successful in fights, more likely to mount and less likely to play than females. Pigs employed different strategies during mixing, the extremes of which were categorised by high-play-low-aggressiveness and vice versa. As expected, aggressive individuals were involved in more fights and won more fights, but suffered more skin lesions than non-aggressive individuals. Pigs that engaged in high-playing were generally the least successful in fights, but suffered fewer lesions and had equal ultimate dominance rank to aggressive pigs. The structure of the mixes changes between weaning and puberty. Fighting ceased sooner during the gilt mix, but aggression was more frequent and more severe. Gilts that reacted aggressively to their piglets were more aggressive and successful in the mix and more ‘reactive’ during farrowing. There were other links between farrowing and mixing behaviour, such as more frequent posture changes but less frequent nesting with greater mix-aggressiveness; indicating that aggressiveness and maternal behaviour are linked through personality.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available