Case studies in antelope aggression control using a GnRH agonist

Maintaining surplus captive male antelope in bachelor groups can result in aggression in some species, leading to injury or death. Suppressing endogenous testosterone using gonadotropin‐releasing hormone (GnRH) analogs has been used in primates to control aggressive behavior, but little information is available on the use of GnRH analogs in nondomestic ruminant species. The aim of this study was to investigate the effect of a slow‐release GnRH agonist (deslorelin) on circulating hormone concentrations, semen and sperm characteristics and behavior in male gerenuk, dorcas gazelle, and scimitar horned oryx. Body weight, testicular volume, circulating hormone concentrations, ejaculate traits, and behavior were recorded before and during deslorelin treatment. A GnRH challenge (with serial blood sampling) was administered to gerenuk and dorcas gazelles before and during GnRH analog treatment. Quantitative behavioral data were collected for gerenuk and dorcas gazelles for 30 min three times a week, starting 1 month before deslorelin treatment, and the mean incidence of combined aggressive behaviors (supplanting, foreleg kicking, sparring, marking, and mounting) was compared before and during deslorelin treatment. No statistical difference (P>0.05) in body weight, semen volume, sperm concentration, percent sperm motility, percent sperm plasma membrane integrity, or percent normal sperm morphology was found before or during deslorelin treatment. The characteristic rise in luteinizing hormone (LH), occurring ～10 min following administration of a GnRH challenge in untreated males, was not evident during deslorelin treatment, although tonic LH concentrations were maintained. No differences (P>0.05) in the mean incidence of any aggressive behavioral traits in gerenuk or dorcas gazelle were detected before and during deslorelin. The absence of a GnRH‐induced increase in serum LH in treated males indicated that deslorelin suppressed pituitary responsiveness to endogenous GnRH, but that the continued tonic production of LH was sufficient to maintain testosterone production, aggressive behavior, and subsequent semen production. Zoo Biol 21:435–448, 2002. © 2002 Wiley‐Liss, Inc.