Abstract:
Previous research suggests a link between litter size in ewes and differential excretion of fecal hormones. An accurate test for fetal number would be useful to sheep producers and a fecal hormone response could be utilized in such a test. Fifteen previously categorized fecal hormones were analyzed within fecal samples collected from n=5 single-bearing ewes, n=1 8 twin-bearing ewes, and n=6 triplet-bearing ewes. Samples were collected at a mean of 75, 95, 125,
and 145 days gestation (gestation length=150 days). Genotypic differences were detected in individual hormone amounts at days 75-95 and litter size differences were detected at days 125-145. At day 75, 20a-hydroxy-5a-pregnan-3-one and 20a-hydroxy-53-pregnan-3-one were different between whiteface and blackface ewes (p<0.05). At day 95, 20a-hydroxy-5a-pregnan-3-one and 20(3-hydroxy-53-pregnan-3-one were different between whiteface and blackface ewes. At day 125, 33-hydroxy-5a-pregnan-20-one, 5a-pregnane-33,20a-diol, and 5apregnane- 33,203-diol differed between single and multiple-bearing ewes. 5apregnane-33,203-diol also differed between twin and triplet-bearing ewes. At day 145, 5a-pregnane-33,20a-diol, 5a-pregnane-33,203-diol, 53-pregnane- 33,20a-diol, and 53-pregnane-3a,20a-diol differed between singles and multiples. 5a-pregnane-33,20a-diol, 53-pregnane-3a,20a-diol, and 33-hydroxy-5a-pregnan-20-one differed between twins and triplets. Total lamb mass (in twinbearing ewes) was related (r-0.50) to concentrations of 5a-pregnane-33,20adiol
and 5a-pregnane-33,203-diol at day 145. However, many remaining unexplainable variations in concentrations between ewes decrease confidence that hormone concentrations can be used in a test to predict litter size.
