Monitoring the reproductive status of female gorillas (Gorilla gorilla gorilla) by measuring the steroid hormones in fecal samples

The reproductive status of female gorillas (Gorilla gorilla gorilla) was estimated by measuring the sex steroid hormones in fecal samples instead of in blood samples. Fecal samples from female gorillas were used to examine the reliability of this non-invasive assay system, which included the extraction method for estradiol-17β (E₂) and progesterone (P) from fecal samples. Fecal samples from three female gorillas were collected daily for about 55 days, and fecal E₂ and P were assayed to clarify the fluctuation patterns of these steroids in the feces. Fecal sampling from one female was repeated for another 50-day period (starting 75 days after the end of the first observation period) and assayed to confirm if the menstrual cycle of this subject was ovulatory. Although fecal E₂ concentration measurements were quantitative by using this assay system, fecal P concentration measurements were semi-quantitative. Relative amounts of fecal P in fecal samples were estimated by using the values of B/B₀ (bound/total binding in the radioimmunoassay system). Two of the four fluctuation patterns of fecal hormones observed throughout the menstrual cycle for the three female gorillas were typical for normal ovulatory cycles. In the subject observed for two periods, one pattern was typical and the other atypical. The results show that this non-invasive method is simple and practical for monitoring the reproductive status of great apes as well as Old World monkeys.