Physiological and reproductive correlates of behavioural strategies in female domestic pigs

Abstract

Thirty-seven pregnant primiparous domestic pigs, Sus scrofa, were introduced into a large indoor pen. The pigs were divided into three groups according to their ability to displace others in agonistic interactions and the behavioural characteristics of these groups were investigated. High Success pigs were able to displace at least as many individuals as displaced them. They were characterized by low levels of inactivity, high involvement in social interactions and high aggression. No Success pigs never displaced any other pig and were most inactive, least aggressive and showed low involvement in social interactions. Low Success pigs were able to displace some pigs but were more often displaced themselves. They were aggressive, despite their relative lack of success, and experienced the highest levels of aggression from and displacement by others. During the first month in the group, High Success pigs gained the most weight. Low Success pigs had the highest basal levels of salivary cortisol and showed the highest peak cortisol levels in response to an adrenocorticotrophic hormone challenge test. At the first parturition, Low Success pigs produced the lowest weight of piglets born alive. Hence there were more adverse effects associated with being aggressive and often displaced than with being aggressive and usually winning, or being unaggressive and involved in few interactions. The strategy used to cope with the social environment may be as important as the success achieved in agonistic interactions, at least in terms of consequences for physiology and reproduction.