Seasonal and Nutritional Influences on Growth Hormone and Thyroid Activity in White-Tailed Deer

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Abstract
Blood samples were drawn monthly for 21 mo. from 4 penned adult female white-tailed deer (O. virginianus) on high diet, 6 does on low diet, and for 6 mo. from 3 does semistarved in winter and spring. Growth hormone (GH) showed no difference (P < 0.01) among diets, but was elevated in late spring and summer in all groups. Thyroxine (T4) and triiodothyronine (T3) increased significantly in late spring, presumably in conjunction with advanced pregnancy. Levels of T4 and T3 between winter and summer were not different for either the high- or low-diet deer. Does on high diet exhibited greater amounts of T4 and T3 during winter and early spring compared to low-diet animals. The T4 and T3 levels dropped sharply throughout winter in the semistarved does. Decreased circulating thyroid hormones may serve as a mechanism for reducing energy requirements when deer are confronted with acute winter malnutrition. Measurement of serum T3 appears to provide a particularly valuable indicator of nutritional stress during winter and probably other periods.