Diurnal Variation of Serum Concentrations of Cortisol, Testosterone, and Progestogens in Asian (Elephas Maximus) and African (Loxodonta Africana) Elephants

A more complete understanding of factors influencing reproductive capacity is needed to benefit Asian (Elephas maximus) and African (Loxodonta africana) elephants whose population numbers are declining. Specifically, investigating reproductive hormonal dynamics could hold the key to improving artificial reproductive techniques and contribute to better understanding of inter- and intrasexual interactions. To our knowledge, this is the first project to examine diurnal variation of progesterone, testosterone, and cortisol using serum samples in African and Asian male and female elephants. Blood samples were collected from eight elephants at Riddles Elephant and Wildlife Sanctuary. The study animals included two Asian females, one Asian male, one African female, and four African males. Thirty blood samples were obtained from each animal over a fifty-eight hour period. Serum was assayed using radioimmunoassay (RIA) procedures for concentrations of progesterone, testosterone, and cortisol. Statistical analysis was performed using SPSS 11.0, GLM repeated measures ANOVA. A significant difference was found across time in cortisol values, F(29,230)=8.13, p\u3c.001, n²=.537. Although there were several possible cyclical trends, a quintic trend was the best fit over the fifty-eight hour time period, with F(1,7)=59.52, p\u3c001, n²=.895. Cortisol levels were highest in the morning and lowest in the evneings. Testosterone also shows a possible multiphasic trend but the small sample size had high variability and showed no statistical significance. Future test on progesterone should focus on elephants in the luteal phase of the estrous cycle. The small sample size in this study did not allow statistical analysis of progesterone