Evidence of higher levels of testosterone during the velvet period in muntjac than in other cervids.

Previous studies have shown that despite having a clear seasonal fluctuation in fecal testosterone concentration, the significantly lower testosterone levels found in velvet stags of the nonseasonal breeder muntjac (Muntiacus sp.) apparently did not stop their spermatogenesis as in other deer species. In the present study, in vitro cultivated Leydig cells isolated from adult stags of three native deer species of Taiwan were treated with androstenedione, with or without adding human chorionic gonadotropin. Results showed that, unlike the two seasonal breeders, sika deer (Cervus nippon) and sambar deer (Rusa unicolor), Leydig cells of velvet muntjac had no dramatic reduction in or even maintained the full capability of their testosterone productivity compared with the hard-antlered stage. The decrease in fecal testosterone level observed earlier in muntjac during the velvet period was probably due to a reduction of number of Leydig cells. These results support the hypothesis that testosterone production in muntjac during its velvet period might never be low enough to trigger the quiescent phase of the reproduction cycle.