The Effect of Exogenous Progesterone Administered Intravaginally, via Cidr, on Embryo Survival in Beef Cattle

Five hundred forty-six postpartum, multiparous and primiparous beef cows at the University of Illinois Dixon Springs Agricultural Research Center (Simpson, Illinois) were used in this experiment. All cows were administered Syncro-Mate B (SMB) for estrus synchronization and were bred from a timed AI about 48 hours after SMB implant removal. Blood samples were collected from all cows on days 0 (AI), 5, 14, 22, and 24 via jugular venipuncture and analyzed for progesterone concentrations using a validated ELISA. Progesterone data was used to determine estrus-cycling status and to monitor corpus luteum development and function. On day 5, one half of the cows were administered an intravaginal progesterone insert (IPI) containing 1.9 g of progesterone. Pregnancy was determined on day 28 via transrectal ultrasound examination. Pregnancy data was analyzed as a 2 x 2 factorial with estrus-cycling status and treatment as the main effects. IPI treatment improved (P = .03) pregnancy rates in estrus-cycling cows, but there was a tendency (P = .06) for pregnancy rates to be lower in treated cows that were previously anestrous.