• pigtailed macaques;
  • ovulation;
  • pregnancy;
  • estrogenic steroids;
  • estradiol-17β


A practical method for the quantitative measurement of the estrogenic steroid estradiol-17β in the feces of pigtailed macaques (Macaca nemestrina) is described. The method, which includes homogenization, filtration, ether extraction, and sephadex purification, produces an 85.3% recovery of 3H-estradiol. Comparable recovery of 3H-progesterone (64.1%) and 3H-testoster-one (67.9%) is also obtained. Estradiol, measured by radioimmunoassay methodology, has inter- and intra-assay variations of 7.1% and 4.3%, respectively. Linearity of estradiol was checked by varying the amount of feces analyzed. Results show a correlation of 0.9945, Y = 32.526x + 0.205. Accuracy of estradiol, determined by adding radioinert estradiol to the feces before homogenization, was 98.7% with a correlation of 0.9950, Y = 1.027x − 0.543. The menstrual cycles of several animals were analyzed and corresponded well with serum levels of estradiol-17β. Similar correspondence was obtained in matched fecal and serum samples from pregnant animals. These methods provide a practical and accurate solution to the problem of collecting hormone data in field studies without the potential complications of capture in laboratory research.