Seasonal levels of cortisol and thyroid hormones in intact and castrated mature male white-tailed deer

Abstract

Plasma L-thyroxine (T4), triiodo-L-thyronine (T3), and cortisol concentrations were measured seasonally in castrated and intact mature white-tailed deer. Both intact and castrated bucks exhibited a statistically significant seasonal rhythm in plasma T4 levels. However, the overall values in the castrated bucks were about 15% lower than in intact animals. Seasonal changes in plasma T3 levels were only found in the intact bucks, with highest values in the April – May period. Two peaks (in June and October) of plasma cortisol were detected in castrated bucks, but only one peak (in the September–October period) was found in intact bucks. In a second experiment in which cortisol levels were measured in "excitable" and "calm" intact bucks, there was no noticeable seasonal rhythm of cortisol in the "excitable" group, but a clear seasonal pattern, with a distinct peak in the October–November period, in the "calm" animals.