Rank-dependent plasma levels of LH, FSH and testosterone in male pudu (Pudu puda) after GnRH administration

Pudu (Pudu puda) is the smallest deer of the world. It exhibits a unique seasonal cycle of reproduction, characterized by the biannual peaks of LH and testosterone. In order to elucidate the regulation of reproduction in pudu, plasma concentrations of LH, FSH and testosterone were measured in 3 pairs of adult males (dominant and subordinate), sampled before and after intramuscular administration of GnRH (50 μg/deer) given at the end of January, one month before the onset of the rut. The hormonal response to GnRH, studied in three pairs of bucks (each pair sharing one pen) was evaluated according to dominance relationship. Unlike the subordinate bucks, the dominant-animals responded to pretreatment procedures with rising levels of all three hormones. In all deer, GnRH administration substantially increased LH and testosterone levels, whereas FSH levels did not change significantly. The elevation in testosterone levels after GnRH was significantly higher in dominant bucks, as compared to subordinate ones. Conversely, an opposite trend, higher LH values were detected in the subordinate deer. The variation of FSH levels after GnRH did not differ between both groups. The data from pudu were compared to GnRH stimulation tests performed in other cervids.