Case studies in antelope aggression control using a GnRH agonist

Abstract

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 B10 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.

Morphofunctional alterations in testicular cells of deslorelin‐treated boars: an immunohistochemical study

“…Previously, a decrease in testicular weight has been described after GnRH antagonist administration in early postnatal pigs (Ziecik et al,'89). It is worth mentioning that persistent GnRH-agonist administration either significantly reduces testicular volume and serum concentration of testosterone as reported in adult rhesus monkeys, dogs, rodents (for a review, see Adams, 2005), and boars in our study, or does not induce a decrease in testosterone secretion as shown in bulls and rams (Aspden et al, '97;Jimenez-Severiano et al, 2007), antelopes (Penfold et al, 2002), and tammar wallaby (Herbert et al, 2004). These observations indicate that the response after prolonged exposure to the agonist appears to be species dependent.…”

Contraception

“…25 In these species, GnRH agonists succeed in blocking the pulsatile but not basal secretion of LH and testosterone, leaving sufficient testosterone to support spermatogenesis and male behavior. 25 In these species, GnRH agonists succeed in blocking the pulsatile but not basal secretion of LH and testosterone, leaving sufficient testosterone to support spermatogenesis and male behavior.…”

Effect of progestins on serum hormones, semen production, and agonistic behavior in the gerenuk (Litocranius walleri walleri)

“…In captivity, space limitations often warrant that surplus male hoofstock are maintained in bachelor groups, but inter-or intraspecific aggression can be problematic in some species [Patton et al, 2001;Penfold et al, 2002]. The gerenuk is a medium-sized east African antelope species.…”

“…Reducing testosterone concentrations has been shown to modify aggressive behavior in domestic species [Martin and Lindsay, 1998] and in the fringe-eared oryx [Patton et al, 2001]. A previous study investigated the use of a GnRH analog in gerenuks to reduce testosterone by acting at the level of the pituitary and decreasing circulating luteinizing hormone (LH) [Penfold et al, 2002]. However, because the mechanism of action of GnRH analogs seems to be different in bovids [D'Occhio and Aspden, 1996;Aspden et al, 1997;D'Occhio et al, 2000, Penfold et al, 2002 compared to other taxa tested [Bertschinger et al, 2001;Munson et al, 2001;Trigg et al, 2001], serum LH and testosterone were not reduced and aggressive behavior was unmodified [Penfold et al, 2002].…”