Effect of testosterone treatment on the antler cycle of an Indian hog deer (Cervus porcinus) with low endogenous level of testosterone
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The antler cycle in deer is hormonally controlled, primarily by testosterone. Growth of antlers and velvet occurs when the plasma testosterone concentration is low. Antlers harden during peak secretion testosterone (rut) and are cast when it precipitously declines at the end of the breeding season. At the San Diego Wild Animal Park, Indian hog deer (Cervus porcinus) shed velvet in October or November and cast antlers in May, with some variation. An 11-yr-old male was noted in December to have failed to shed an abnormal-appearing velvet. The animal did not cast antlers the following spring, and a distinct shrinkage and hardening of one testis was noted on palpation. A small volume of aspermic semen was produced by electroejaculation. When the antlers had not cast by the next spring, the male was treated with testosterone implants to raise the plasma testosterone concentration. It was hoped that implant removal would mimic the postbreeding-season decline in testosterone secretion and cause casting of the antlers. At the initiation of treatment, serum testosterone concentration was 78 pg/ml, and both testes were indurated. High levels of testosterone (652 pg/ml) were achieved with 2 wk of treatment, with a maximal level of 1,000 pg/ ml attained by 10 wk. Velvet was shed, and the antlers became a "hard rack" within 8 wk. However, a small area at the base of one antler retained blood supply, and treatment with testosterone for 11 wk did not result in complete regression of the blood supply. Implant removal was followed within 1 wk by a return to pretreatment serum testosterone level, but the antlers were not cast. The male did not exhibit elevated testosterone in response to gonadotropin-releasing-hormone challenge. The hog deer was euthanized due to severe, chronic carpal arthritis. Necropsy did not reveal the cause of testicular demise, and it was assumed that traumatic injury to the testes during antler growth interrupted the normal antler cycle in this animal by ablating testosterone support. Copyright 1996 by American Association of Zoo Veterinarians.
