Hormonal regulation of reproduction and the antler cycle in the male Columbian black-tailed deer (Odocoileus hemionus columbianus). Part II. The effects of methallibure and hormone treatment

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Abstract
Methallibure, a non-steroidal inhibitor of gonadotropin secretion, arrested antler growth and suppressed reproduction. The administration of prolactin, pregnant mares'' serum gonadotropin (PMS) and some androgenic steroids in methallibure-treated deer during June and July failed to stimulate antler growth, but human chorionic gonadotropin (HCG) did rejuvenate it in 1 instance. None of these hormones was effective in completely restoring reproductive function, although PMS and HCG stimulated the production of enough testosterone to induce velvet sheeding. During the normal period of antler growth, the testes of methallibure-treated deer did not respond to the exogenous administration of HCG by secreting testosterone, whereas both PMS and prolactin were effective in this respect. After the administration of PMS, HCG stimulated testosterone production, but it was ineffective in deer previously treated with prolactin. When methallibure treatment was terminated in the fall, testosterone production and spermatogenesis recovered, but the deer that had previously received prolactin did not produce mature sperm until the next spring. The testicular response may depend on the temporal sequence and on the type of hormonal stimulation. The hypothesis that a gonadotropin is responsible for stimulating antler growth is supported.