Modifications of a field method for fecal steroid analysis in baboons

Abstract

By extracting steroid metabolites from feces, researchers can track endocrine activity noninvasively in free-ranging animals. Sample preservation is a critical component of such methods because steroid metabolites rapidly decompose. Here, we describe a method for preservation, field extraction, and radioimmunoassay of steroid metabolites (estradiol, progesterone, glucocorticoids, and testosterone) from the feces of wild female baboons (Papio spp.). This method is a modification of that developed by Stavisky [Socioendocrinology: noninvasive techniques for monitoring reproductive function in captive and free-ranging primates. PhD, Emory University, 1994.], which employs reversed-phase octadecylsilane cartridges to extract steroids from feces. In addition to providing physiological validation for this method, we examine variation in steroid concentration across different (1) collection times (morning vs. afternoon), (2) methanol extraction treatments (homogenized vs. hand-mixed), and (3) solid-phase extraction times (2 vs. 10 h after collection). We then examine the stability of sample storage at ambient and subzero temperatures to determine whether storage time significantly alters steroid concentrations. Our results show that hormone concentrations do not differ between morning and afternoon samples, homogenization yields significantly higher fecal steroid concentrations, and fecal steroids are stable in a methanol/acetone solution for up to 10 h. When stored at ambient temperatures, only glucocorticoid metabolites had some degradation over a period of up to 40 days. However, when stored at -10 degrees C, no significant steroid changes were observed for up to 400 days. This method is particularly suited for behavioral research because it permits delays between sample collection and sample processing, thus allowing behavioral observations to continue.