Relationship between agonistic behaviour and propensity to develop excessive drinking and chain manipulation in pigs.

Abstract

Consistent individual differences in animals' responses to different stressful situations may indicate the involvement of a single behavioural and neurological mechanism across these situations. Two replicate groups of sixteen food restricted pigs were subjected to a group feeding competition test where group members were required to compete over a food source. All agonistic interactions were scored and ranked dominance scores were calculated. The pigs were subsequently put into two different forms of restrictive housing (restraint or loose), with half of the pigs food restricted. No housing effects were found. Only food restricted pigs developed excessive drinking and chain manipulation, but large individual differences existed. Pigs ranked high in dominance score were found to significantly increase their drinking levels over the experimental period of three months, having significantly higher drinking levels than low ranking pigs in the second and third month. No significant relationship was found between ranked dominance score and levels of chain manipulation. The present results suggest that in pigs differences in the propensity to develop forms of excessive drinking under restrictive housing and feeding conditions are related to agonistic tendencies in a group feeding competition test. These data also suggest that excessive drinking and chain manipulation are at least in part based on different behavioural and presumably neural mechanisms.