Summary. A rapid method was developed for extracting and assaying oestradiol and progesterone in faeces (n = 242) of female yellow baboons, free-living in Tanzania. Dose response studies generated slopes of 1·02 (r 2 = 0·99) for oestradiol and 1·09 (r 2 = 0·99) for progesterone, suggesting that this method accurately measured these steroids in faeces. Parallelism was proved by demonstrating that slopes produced from serially diluted samples were not different from those generated from standard curves (mean P value = 0·53 ± 0·17 for oestradiol and 0·44 ± 0·13 for progesterone). Faecal progesterone concentrations measured over several cycles in 2 females increased and decreased in correspondence to visual markers of the luteal phase (i.e. the period between sex-skin detumescence and menses), but the presumed preovulatory oestradiol peak was not observed consistently in all cycles. Progesterone profiles during early to midgestation in 3 females confirmed pregnancy by 25 days (14%) of gestation. Oestradiol profiles were more variable and were not indicative of pregnancy until 40 days (22%) of gestation. Radiolabel-infusion studies revealed that 32% of progesterone (n = 2) but only 11% of oestradiol (n = 2), was cleared through faeces. The latter findings may account for the greater variation observed in temporal oestradiol patterns during the baboon menstrual cycle and pregnancy. Compared with previous techniques, these new methods (i) save considerable time in assaying raw material and (ii) result in high extraction recoveries of faecal steroids ∼88% for oestradiol and 91% for progesterone). This approach may be particularly useful for studying physioloical function and endocrine–environmental interrelationships in free-living primate species.
Keywords: faeces; oestradiol; progesterone; free-ranging; baboon