Reproductive endocrinology of bull elephants

To better understand the hormonal mechanisms controlling musth in elephants, concentrations of testosterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin, cortisol, thyroxine (T4), tri-iodothyronine (T3), and thyroid stimulating hormone (TSH) in captive bulls were monitored throughout the year. Blood was collected weekly to monthly from twenty bulls (11 African, 9 Asian) for periods of six months to eight years. Nine bulls exhibited musth for periods of two to eight months each. Concentrations of all hormones varied within individuals. Mean testosterone concentrations increased during the summer (June--September) in African, but not in Asian elephants. Mean thyroid hormone concentrations decreased during the summer. Testosterone concentrations correlated with free T4 and T3 in seven individuals, with LH in five individuals, and with cortisol in six individuals. Continued research is needed to study factors related to bull behavior to better understand the impact of musth on the reproductive success of captive bull elephants.