Hormonal correlates of hypophagia in white-tailed deer.

Deer exhibit a number of adaptive annual changes in common with hibernators. Each winter deer have a period of voluntary hypophagia and losses of body weight. This is accompanied by a shift to fat metabolism and increased recycling of urea nitrogen to maintain positive nitrogen balance. Deer also show alterations in activity patterns and decreased metabolic rates, heart rates, and body temperatures during winter. Male deer exhibit an additional period of hypophagia associated with rut. Rut-associated hypophagia is either directly controlled by serum testosterone or internally coupled to the annual testosterone cycle. The adaptive value of rut-associated hypophagia is unknown but may be associated with insuring reproductive success. Both winter and rut-associated hypophagia are most likely synchronized to the environment by photoperiod. The winter adaptive changes may be caused by a primary alteration in appetite control with secondary changes in thyroid hormone economy, or the hypophagia may be independent but internally coupled to other neuroendocrine changes.