Serum testosterone, 5-alpha-dihydrotestosterone and different sex characteristics in male fallow deer (Cervus dama): a long-term experiment with accelerated photoperiods.

To investigate the photoperiodic influence on androgen, testis volume, neck girth, and antler-cycles, five fallow bucks were exposed consecutively to different accelerated photoperiodic cycles (three 6-month, three 4-month, and one 3-month cycle). All parameters immediately followed artificial light cycles. Unlike in natural conditions, antler casting, regrowth, and velvet shedding occurred at decreasing day-lengths. The experiment provided further evidence that in fallow bucks the reproductive system is under strictly photoperiodic control and directly and/or indirectly dictates the course of the antler cycle via gonadal hormones. Depending on the test-system, the experiment revealed similar threshold values for the effect of testosterone (T) and/or 5-alpha-dihydrotestosterone (DHT) concentrations on the antler cycle as previously detected in fallow bucks living under natural conditions. Antlers were cast when T levels dropped below 3 ng/ml, and velvet shedding occurred after T and/or DHT values reached at least 5 to 7 ng/ml. In all cases, amplitudes of androgens remained lower than observed under natural conditions. Frequently during early antler growth, DHT values appeared higher than T levels. With increasing acceleration of the photoperiod, the antler cycle achieved limits of adaptation. The faster the photoperiods were accelerated, the smaller the antlers were developed. In addition, the antler tips were porous, blunt, and not completely mineralized. In all animals, accelerations of the photoperiods evoked phase displacements between measured parameters, pointing to an increasing internal desynchronisation. The present results indicate that the whole reproductive system of fallow deer is directly controlled by the photoperiod and that related morphological and physiological processes are indirectly determined by photoperiodic changes.