The endocrine control of the initiation and growth of antlers in white-tailed deer.

Five fawn and 5 adult white-tailed deer (Odocoileus virginianus) were maintained in individual pens, fed a complete diet, and bled bi-weekly for one year. Blood serum was analyzed for testosterone (T), androstenedione (A), thyroxine (T4), calcium (Ca), phosphorus (P) and alkaline phosphatase (AP). Adults grew velvet antlers from mid-April and shed their velvet in mid-September. Hardened antlers were cast in March. Fawns grew velvet antler buttons which hardened in February and cast in March, prior to the growth of the first antlers. Adults had higher (P less than 0.05) titres of T and A over the year. Fawns had higher T4 levels and AP activity (P less than 0.05), while Ca and P levels were not different between the groups (P greater than 0.05). In the adults, T peaked in December and April and was correlated with the periods of hard antlers and the initiation of antler growth. In the fawns, T peaked in November and April and was correlated with hardened buttons and the initiation of the first antlers. Adult A peaked in June but hit nadirs in May and July and generally was not correlated with the antler cycle. In the fawns, A was similar to the T cycle. Thyroxine was relatively constant over the year in adults, but was elevated in the winter in fawns during the period of hardened buttons. Calcium and P levels were relatively constant throughout the year in both groups. AP activity was elevated over winter in adults and then decreased sharply when antlers were cast. Activity increased gradually again as new antlers grew. AP activity in fawns was elevated over the winter and spring and gradually declined as the first antlers developed.