Enhanced progesterone and pregnancy rate after gonadotropin administration in lactating ewes

Estrus was induced during March and April in 50 lactating ewes that were 20 to 31 d postpartum. Following estrus induction, ewes were treated with either saline or human chorionic gonadotropin (hCG; 100 IU) on d 11, 12 and 13 after mating. Regardless of whether ewes were later diagnosed as pregnant or not, treatment with hCG increased serum progesterone concentrations compared with concentrations observed in saline-treated ewes on d 12, 14 and 16 after mating (P less than .01). Pregnancy rate was higher in ewes treated with hCG than that of ewes treated with saline (58 vs 29%; P less than 0.5). Data from the present study indicate that it is possible to increase pregnancy rate in lactating, anestrous ewes after artificially-induced estrus by administering hCG.