Social relationships, aggressive behaviour and emotional reactivity in Ungulates : influences of sex steroids

Abstract

Aside from their effects on sexual motivation and reproductive behaviour, sex steroids influence a variety of other behaviours, especially social relationships, agonistic behaviour and emotional reactivity.

Our knowledge of the hormonal influences on these behaviours in ungulates is somewhat fragmentary despite the fact that the endocrine system of the domestic species is well known. However, the importance of understanding the behaviours that are susceptible to be influenced by sex steroids is evident for the efficient management of domestic species.

There are well established sex differences in aggressive behaviour, ability to dominate, social role and fear reactions. These differences are influenced by androgens. Variations in agonistic and territorial behaviour related to natural variations in hormonal levels have been demonstrated in many species. Experimental manipulation of hormonal levels by castration and hormone replacement therapy, and experimental hormonal treatments have confirmed the role of sex steroids. In particular, treatment of both males and females with androgens enhances their dominance ability and reduces their fear reactions in both social and non social situations. Moreover, this effect persists long after the end of treatment. It is possible to influence the future social rank of an animal by giving it such a treatment. However, the mechanisms by which androgens act remains unclear.

Since male animals are being increasingly reared in groups, the study of the relationship between androgens and aggressiveness is of particular interest. In addition, emotional reactivity is involved in the ability of the animals to adapt to their environment. The study of the factors (including sex steroids) capable of influencing this intermediate variable is therefore important in order to develop management techniques which take animal welfare into account.