Use of Fecal Steroid Metabolites to Estimate the Pregnancy Rate of a Free-Ranging Herd of Tule Elk

Abstract

The ability to measure reproductive hormones in urine and feces permits physiologic evaluations of free-ranging animal populations. The data from previous reports indicate specific events such as gonadal recrudescence, ovulation, conception, pregnancy, and lactation can be detected and defined by fecal hormone analysis in a wide range of animals. The present study was undertaken to determine if combined data from a ongitudinal and cross-sectional hormonal study of free-ranging cow tule elk (Cervus elaphus nannodes) and simultaneously collected observational data would permit an accurate estimation of the pregnancy rate of the population, Ovarian and placental function were monitored in 34 radiocollared cow tule elk from the onset of ovarian recrudescence in the summer of 1996, through the calving season in the spring of 1997. Estrogen and progesterone metabolites were measured by enzyme immunoassay (EIA) in fecal samples collected from both radiocollared and uncollared cows. The radiocollared cows were located and identified for individualized observations of fecal deposition and later confirmation of pregnancy by observation of nursing. Hormonal concentrations from the samples collected from the radiocollared cows in which pregnancy and outcome were known were used to set criteria for designation of a cow as pregnant in the cross-sectional samples collected from a population of approximately 208 uncollared cows. Progesterone metabolite (PdG) concentrations were 100% reliable at predicting pregnancy within the first trimester of gestation through parturition, while estrogen metabolite (E 1 C) concentrations were not a reliable indicator until the last trimester of gestation. A progesterone metabolite concentration > 1.01 ug/g dry mass feces (dmf) after the breeding season was set as confirmation of pregnancy status in fecal samples collected from uncollared cows. Analysis of hormonal concentrations after the 1997 calving season in conjunction with observations of nursing permitted pregnancy detectio estimates via the calving rate of the collared cows for the 1996-97 breeding and calving season. These same parameters were estimated and evaluated in the uncollared cows. Our results provide strong evidence that the measure of fecundity in free-ranging animals can be obtained through fecal steroid analyses, and that this measure is an accurate predictor of fertility.