Variation in metabolic factors and gonadal, pituitary, thyroid, and adrenal hormones in association with musth in African and Asian elephant bulls.

Longitudinal analyses of serum testosterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin, glucose, insulin, triglycerides, cholesterol, total and free thyroxine (T), total triiodothyronine (T), thyroid stimulating hormone (TSH), and cortisol were conducted to investigate pituitary, metabolic, and adrenal changes related to testicular function and musth status in zoo-housed elephant bulls. Blood samples were collected twice a month for 12 months from 14 African and 12 Asian bulls at 17 facilities in North America. Building on previous studies, our results show that musth is associated with increased testosterone, LH, FSH, and cortisol secretion, and a decrease in thyroid hormone (total and free T) production. In addition, glucose and triglycerides were higher during musth than non-musth periods, indicative of altered sugar and fat metabolism. There were significant differences associated with age for LH, FSH and testosterone, all increasing, whereas the glucose-to-insulin ratio (G:I) decreased with age. A species comparison found African and Asian elephants differed in measures of insulin, prolactin, cholesterol and the G:I. Across all hormones, high inter-individual variability was observed, making it difficult to define a general musth endocrine profile or to assess musth status from single samples. These results highlight the need for facilities hosting bulls to closely and consistently monitor each individual from an early age and throughout musth and non-musth periods to determine the pattern for each male.