SUPRESSION OF TESTICULAR FUNCTION IN A MALE ASIAN ELEPHANT (ELEPHAS MAXIMUS) TREATED WITH GONADOTROPIN-RELEASING HORMONE VACCINES

Abstract

The ability to control testosterone concentrations and sperm production is of great interest in both Asian (Elephas maximus) and African (Loxodonta africana) elephants. GnRH vaccination may pose an alternative to surgical castration. This is a case report of a male Asian elephant treated with two commercial GnRH vaccines (Equity and Improvac). Beginning at the age of 7 yr, the male was vaccinated monthly for 6 consecutive months, then every 6 mo and, finally, every 12 to 24 mo over a period of 6 yr. In order to evaluate the GnRH vaccine as a potential method of immunologic castration, behavioral observations, testosterone level analysis, body weights, ultrasound examinations, and semen collection were part of the routine monitoring of this bull (no. 1) and a half-brother (bull 2) who remained untreated and served as control. The results showed a decrease in serum testosterone concentrations after the second booster. Levels stayed continuously below 5.0 ng/ml within the study period. The combined testicle diameter of 9.03 +/- 0.3 cm prior to treatment had decreased to a size of 6.93 +/- 0.19 cm (P < 0.001) when measured 2 yr later. Accessory sex gland fluid content disappeared and penile atrophy was observed. Semen collections yielded no spermatozoa 1 yr after the initial treatment. Bull 1 showed slowed weight gain as compared to bull 2 and, due to its friendly temperament and the absence of musth, remained in free contact. This report documents the GnRH vaccine as a possible noninvasive and inexpensive method for immune-castration.

Use of gonadotrophin releasing hormone (GnRH) vaccines for behavioural and reproductive control in managed Asian elephantElephas maximusand African elephantLoxodonta africanapopulations

“…Reproductive organs (accessory sex glands and testicles) were measured by ultrasound and semen samples were obtained by transrectal prostate massage or, in case of wild bulls, by electroejaculation. Reproductive‐organ size decreased after two injections and was significantly decreased (by up to 60%) at the end of the respective studies after 3·5 years (Lueders et al ., ) and 6 years (Lueders et al ., ).…”

“…Although at the time of writing there are no long‐term antibody titre studies available, in elephants, our experience and the published studies on behaviour and hormone levels suggest that injection intervals may be extended after initial monthly or three‐monthly injections (De Nys et al ., ; Lueders et al ., ).…”

“…Testosterone secretion Studies have shown that musth in elephants appears to be under the control of the HPG-axis (Lincoln & Ratnasooriya, 1996). Injection with exogenous GnRH induces a surge of LH secretion, followed by the release of testosterone (Somgird, Sripiboon et al, 2016) Thus, it is not surprising that immunization against GnRH led to lowered testosterone and to cessation of musth in elephants in the available studies (De Nys et al, 2010;Rajapaksa et al, 2010;Lueders et al, 2014Lueders et al, , 2017Somgird, Homkong et al, 2016). The effect of the GnRH vaccine on blood serum (Somgird, Homkong et al, 2016) or faecal androgen (Lueders et al, 2017) levels was measured.…”

“…In a study on African elephants managed using unrestricted contact at private facilities, behaviour was modified in certain individuals, which appeared calmer and more attentive to their handlers (De Nys et al, 2010). Only one subadult, captive-born Asian elephant male was treated and monitored for testosterone and behaviour (Lueders et al, 2014). This male (7 years if age at the beginning of the study) was regularly vaccinated for 6 years (initially monthly, then every 6 months and then yearly), and showed no testosterone production and no sexual interest or aggression.…”

Mucosal Vaccine Development for Veterinary and Aquatic Diseases

“…To be adopted for use, mucosal immunocontraceptive vaccines must be effective in the target animals and have limited or no effect on nontarget animals which may include humans who consume the meat, eggs, or milk from the targeted species. For zoo animals, such as captive African and Asian elephants, altering sex hormone levels in male or females may be advantageous in that they reduce aggression during musth season, but the alterations can also interfere with dominance hierarchy in a herd, which may not be advantageous [59,60]. Further, use of oral bait delivery systems should, if possible, be designed in such a way as to reduce consumption by unintended target species.…”