Early Pregnancy Determination Using Serum Progesterone Concentration in Bighorn Sheep

Abstract

We determined serum progesterone concentrations of 25 female bighorn sheep (Ovis canadensis) in February 1984 and January 1985 as an indicator of pregnancy. Accuracy in predicting pregnancy was 90% in 1984, 80% in 1985, and 84% over both years. Most misclassifications were attributed to sampling too close to estrous. Accuracy may be improved if sampling occurs >16 days after the conclusion of breeding activity. Serum progesterone concentration is an accurate indicator of early pregnancy in bighorn sheep. J. WILDL. MANAGE. 52(4):610-612 Detection of pregnancy early in gestation is required to accurately determine reproductive rates and estimate early prenatal loss. Several techniques are used for pregnancy determination of domestic animals; some have been used successfully for wild animals (e.g., rectal palpation [Greer and Hawkins 1967, Follis and Spillet 1974], laparotomy [Zwank 1981], ultrasound [Smith and Lindzey 1982, Harper and Cohen 1985], and hormonal assay [Ramsay and Sadleir 1979, Whitehead and McEwan 1980]). Blood progesterone concentrations have been shown to be accurate indicators of pregnancy in domestic (Bassett et al. 1969) and bighorn females (Ramsay and Sadleir 1979, Whitehead and McEwan 1980). Progesterone determination has the advantage of relatively simple sample collection (if animals can be trapped and handled) and relatively inexpensive analysis. Our study was designed to determine if progesterone serum concentrations indicated early pregnancy in free-ranging bighorn sheep. Serum progesterone concentrations were assayed by B. Pettitjean (Anim. Sci. Dep., South Dakota State Univ.). We thank Custer State Park (CSP) personnel and students from South Dakota State University for assistance with trapping. Funding was provided by a grant from the Foundation for North American Wild Sheep, Custer State Park, and federal aid administered by South Dakota Department of Game, Fish and Parks.