Effect of gonadectomy, season and the presence of female tammar wallabies (Macropus eugenii) on concentrations of testosterone, luteinizing hormone and follicle-stimulating hormone in the plasma of male tammar wallabies.

Concentrations of FSH, LH and testosterone in plasma were measured in groups of adult male tammar wallabies before and after gonadectomy, and during the breeding and non-breeding seasons. Gonadectomy resulted in a rapid fall in plasma testosterone to undetectable levels by day 2, and significant increases in plasma LH and FSH levels. The concentrations of FSH, LH and testosterone did not change significantly between the non-breeding and breeding seasons in groups of male wallabies maintained in the absence of females. However, when male wallabies were associated with sexually mature females there were significant three- to fourfold increases in concentrations of LH and testosterone in plasma at the commencement of the breeding season. The observed increases in LH and testosterone were highly synchronized in the eight animals studied and occurred approximately 2 weeks before the synchronous onset of mating. Concentrations of FSH did not change significantly at this time.