Control of testosterone secretion, musth and aggressive behaviour in African elephant (Loxodonta Africana) bulls using a GnRH vaccine

Abstract

Aggressive behaviour with or without musth can constitute a serious management problem for captive and free-ranging African elephant bulls, and can endanger the lives of both animals and man where such elephants are kept. Generally, bulls in musth have to be restrained to such an extent that it becomes an animal welfare issue. Often euthanasia constitutes the only resort since there are as yet no practical ways to control musth. Musth and aggressive behaviour seem to be related to high concentrations of testosterone. In this study, the effects of a GnRH vaccine on faecal epiandrosterone and behaviour were tested in six African elephant bulls. Anti-GnRH antibody titres could be measured in three bulls after immunization. Faecal cortisol metabolites were also monitored in order to explore a possible link with androgen secretion. The vaccine (GnRH-tandem-dimer conjugated to ovalbumin, Pepscan Systems, the Netherlands) was used with either Montanide ISA 51 or Covaccine adjuvants. Five elephant bulls were vaccinated with 2 mg GnRH 3 or 4 times at approximately 3-week intervals by means of darting or hand-injection. Faecal samples were collected during each week prior to vaccination and 4 months after the last vaccination. Behaviour was monitored concurrently. Three of the bulls responded to the vaccine with significant decreases in faecal epiandrosterone concentrations. The first bull had been exhibiting aggressive behaviour with temporal gland secretion for some time. Three vaccinations were carried out using ISA 51 adjuvant and the last one using Covaccine. A marked effect was observed on faecal epiandrosterone after the 4th vaccination. He also displayed calmer episodes and a reduction in temporal gland secretion. Because the emulsion formed with ISA 51 proved too viscous for darting purposes, Covaccine adjuvant was used for the remaining bulls. The second bull was extremely irritable and had been damaging properties on a regular basis for months. After the 3rd vaccination, antagonistic behaviour and temporal gland secretion ceased and epiandrosterone concentrations were significantly lower. Increased antibody titres were observed. The third bull was a trained animal that had not exhibited aggressive behaviour before vaccination. Faecal epiandrosterone was reduced after the second vaccination. No changes in faecal epiandrosterone concentrations were observed in the three remaining bulls. One of these bulls, however, was in musth before vaccination and went out of musth 10 days after the first vaccination. Androgen levels were low just before the primary vaccination, which indicates that the primary vaccination may have coincided with the natural end of musth. Cortisol levels increased when musth signs disappeared. The two other bulls had not exhibited aggressive behaviour before vaccination and no behavioural changes were observed after immunization. Positive antibody titres, however, were observed. A positive correlation between androgen and cortisol secretion was observed in these two bulls. The vaccine produced no side effects whatsoever in any of the bulls. The observed improvement in behaviour of bulls that were aggressive prior to vaccination and the absence of adverse side effects, suggest that this method could constitute a way of controlling musth and aggressive behaviour in African elephants. There was, however, marked individual variation in response to GnRH immunization. Possible factors influencing the response of each bull are discussed. Age seems to be important, as the youngest bulls showed a better response in terms of reduced androgen secretion. Moreover, species-specific differences could influence the efficacy of GnRH immunization as well as the detection of hormonal changes after vaccination. The cortisol and androgen metabolite results suggest that a substantial amount of androgens may be secreted by the adrenal glands in African elephants. Observed patterns of hormonal secretion in the musth bull support the hypothesis that high androgen levels associated with musth suppress cortisol secretion. Further work to determine the optimal vaccination protocol is needed in order to obtain marked and consistent responses to the vaccine.