Abstract:
The African wild dog (Lycaon pictus) is the second most endangered carnivore in Africa. Although several high-profile endangered species are imperiled due to poor fertility, inadequate genetic diversity, and a reliance on specific niches, the wild dog is threatened by decreasing land space and human hunting practices. Wild dogs are highly fertile with an average litter size of nine at De Wildt Cheetah and Wildlife Centre. Wild dog males have 3 million to 900 million sperm per ejaculate and 45-75% progressive motility during the breeding season. Wild dogs released into small nature reserves in South Africa experience increased survival rates due to sizeable litters, abundant prey, and increased hunting success along fence lines. Furthermore, the current demand for captive-bred wild dogs is low due to lack of demand by overseas zoos and the inability of nature reserves to accommodate more dogs. Long-acting GnRH analogues have been used for fertility control in many wildlife species. However, dosing and efficacy differ among species and individual animals. This study assessed the efficacy of the GnRH analogue, deslorelin, on reproductive parameters of male African wild dogs. Seasonal effects on reproduction were also evaluated. Captive male African wild dogs housed at the De Wildt Cheetah and Wildlife Centre were administered either a 4.7 mg deslorelin implant (Suprelorin,® Peptech Animal Health (Pty) Ltd, Sydney, Australia; n = 10), an experimental 9.4 mg deslorelin injection (n = 11) or a placebo injection (n = 6). Treatment was administered during the non-breeding season (Month 0), and dogs were assessed at Months 3, 5, 6, and 7. Reproductive parameters evaluated before and after treatment included: serum testosterone, testicular and prostatic volume, and semen quality. Serum testosterone was assessed with a previously validated double antibody DSL testosterone radioimmunoassay kit (Diagnostic Systems Laboratories, Inc, Webster, TX). Testicular volume was calculated from testicular dimensions measured with a calliper and prostatic volume from dimensions obtained by trans-cutaneous ultrasound. Data were analyzed with ANOVA. Although the 4.7 mg deslorelin implant was safe for use in male wild dogs, there was wide variation in efficacy among dogs. The serum testosterone of implant dogs did not decrease to baseline after treatment and only half the dogs administered an implant became azoospermic post-treatment. The experimental long-acting deslorelin injection was ineffective for contraception of male African wild dogs. All three groups of dogs experienced an improvement in reproductive parameters during the months of February through May, the rainy season in northern South Africa and the period during which female African wild dogs enter oestrus, suggesting that a breeding season not only exists in the female African dog but also in the male. Testis and prostatic volume increased, serum testosterone concentrations and semen quality improved during that time of year. Further studies of deslorelin in male wild dogs are warranted to determine the appropriate dose, pay-out pattern, delivery method, and season of delivery necessary for adequate contraception in this species.
