Seasonal relationships of thyroid, sexual and adrenocortical hormones to nutritional parameters and climatic factors in white-tailed deer (Odocoileus virginianus) of south Texas.

Annual cycles of serum testosterone (T), estradiol 17-beta (E), thyroxine (T4), triiodothyronine (T3) and cortisol (C) and their relationship with dry matter intake (DMI), ambient temperature and daylength (DL) were examined in four male and four female white-tailed deer. Serum T in bucks correlated (P less than 0.05) with DMI during the rut. In does, E correlated (P less than 0.05) with DMI and body wt. Both serum T and E were DL and temperature dependent. Serum T4 in bucks correlated (P less than 0.05) with body wt and increasing temperature while T3 correlated (P less than 0.05) with DMI and body wt. In does, T4 was significantly (P less than 0.05) correlated with DMI and body wt, while T3 was not. Serum C levels were not correlated (P greater than 0.05) with either DMI or body wt. It appears that serum T4 and T3 in bucks and T4 in does offer the best year-round indicators of nutritional stress in deer. Male DMI was temperature and DL dependent. In does, only a short-term effect on DMI was found. After the breeding season in bucks, and throughout the year in does, DL and temperature may control intake via the thyroid hormones.