Hormonal regulation of reproduction and the antler cycle in the male Columbian black-tailed deer Odocoileus hemionus columbianus

The hormonal regulation of reproduction and the antler cycle in male Columbian black-tailed deer (Odocoileus hemionus columbianus) was investigated by measuring serum testosterone, testis volume, sperm production and the antler growth cycle of wild deer and of captive deer treated with methallibure and various hormones. A histological examination of the pituitary, adrenals, thyroids, testes and accessory sex glands of normal and methallibure-treated deer was also performed to study the functional relationships of these organs to reproduction and antler growth. Various constituents in the serum and urine of normal and methallibure-treated deer were measured to investigate the effects of methallibure on physiological function. Testosterone secretion, testis volume, sperm production, and the secretory activity of the accessory sex glands were maximal in November, at the height of the reproductive season. During this period the mean serum testosterone level of the adult males was 10 ng/ml, testis volume averaged 30 cm³, and the concentration of sperm in the semen was 100 x 10⁶ to 700 x 10⁶/ml. In winter, the activity of the reproductive organs declined, until a minimum was reached in February or March. The antlers were cast several weeks after the serum testosterone dropped below 1 ng/ml. In spring, a significant increase in spermatogenetic activity occurred, coincident with the initiation of antler growth. Spermatogenesis declined in June and July, but the seminiferous tubules and accessory sex glands were still more active than in late winter. The serum testosterone level however, remained low (