GnRH facilitates copulatory behaviour in geldings
treated with testosterone

M. A. Pozor*, S. M. McDonnell, R. M. Kenney and M. Tischner*

University of Pennsylvania, School of Veterinary Medicine, Section of Reproductive Studies, Kennett Square,
Pennsylvania 19348, U.S.A. and *Academy of Agriculture, Department of Animal Reproduction, 30-095
Krakow, Al Mickiewicza 24-28, Poland

Introduction
    There is growing evidence that gonadotrophin releasing hormone (GnRH) plays an important role in the regulation of sexual behaviour in animals and man. Facilitatory effects on lordosis behaviour have been reported in ovariectomized, oestrogen-treated female rodents (Moss & McCann, 1973; Luttge & Sheets, 1977) and on copulatory behaviour in castrated, testosterone- (T) treated male rodents (MOSS et al., 1975; Boyd & Moore, 1985). In all cases, GnRH effects on reproductive behaviour appear to be dependent on the presence of gonadal steroid. GnRH given intravenously (i.v.) to stallions with inadequate sexual behaviour improves their sexual arousal within minutes of administration (McDonnell et al., 1987). In another experiment, GnRH affected pre-copulatory behaviour of T-treated pony geldings (McDonnell et al., 1989). The present experiment was designed to evaluate GnRH effects on copulatory behaviour in geldings with and without testosterone replacement.