Hormonal regulation of reproduction and the antler cycle in the male Columbian black-tailed deer (Odocoileus hemionus columbianus). Part I. Seasonal changes in the histology of the reproductive organs, serum testosterone, sperm production, and the antler cycle

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Abstract
The hormonal regulation of reproduction and the antler cycle was investigated by measuring serum testosterone, testis volume, sperm production, and the antler growth cycle of wild and captive deer. The functional relationships of the testes and accessory sex glands to reproduction and antler growth were also studied by examining these organs histologically.Reproductive activity was maximal in November when 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 × 106 to 700 × 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. The serum testosterone level, however, remained low until velvet shedding, in late summer.These findings support the hypothesis that the maturation of antlers, shedding of the velvet, and the maintenance of antlers in the hard, functional condition are dependent on testosterone. The possible significance of increased spermatogenetic activity in the spring and its relationship to antler growth are also discussed.