Serum testosterone (T) and 5-alpha-dihydrotestosterone (DHT) in male fallow deer (Dama dama L.): seasonality and age dependence.

1. Seasonal levels of testosterone (T) and 5-alpha-DHT (DHT) were determined by RIA in serum of seven adult male fallow deer living under outdoor conditions (Göttingen, FRG; 51.32 degrees NL). 2. The study, spread over six consecutive years, reveals the following seasonal T changes: Minimum concentrations in November or December, around antler casting and at early antler growing phase; increasing levels in the course of late antler development (mineralization) with relatively high values around velvet shedding; peak levels occurring during onset of rutting period followed by a sharp decrease after the rut; and distinct and oscillating T peaks during late winter and spring. 3. For the first time DHT levels were measured in male cervidae. Surprisingly, large values of DHT were found and occasionally levels were higher than T concentrations, but without a significant annual periodicity. 4. In some individuals maximum DHT values were found shortly before and during the rut. 5. During several months of the annual cycle individual T and DHT profiles showed opposite relationships, particularly during antler growing phase and shortly before antler casting. 6. Around rut the size of T peak levels depends on animal age.