423 - Setting the Cycle for Reproductive Success with a Presynchronization Program in Postpartum Beef Cows

Previous experiments from our laboratory determined that postpartum beef cows with a functional corpus luteum (CL) at the start of an estrous synchronization protocol have greater pregnancy success to FTAI than those that did not have a CL. Therefore, it was hypothesized that incorporation a presynchronization program prior to FTAI in postpartum cows will improve pregnancy rates. The goal of this project was to compare the effectiveness of a presynchronization program prior to the 7d CO-Synch+CIDR fixed timed artificial insemination (FTAI) protocol in postpartum cows. Postpartum cows (n = 310) at two locations were randomly assigned to receive either the presynchronization program, consisting of 2 PGF2α injections 14 days apart and 11 days prior to the start of the 7-day CO-Synch+CIDR protocol, or the 7-day CO-Synch + CIDR protocol. Follow estrous synchronization, all cows were inseminated by trained technicians using semen from bulls of known fertility. Pregnancy status to FTAI was assessed using ultrasonographic diagnosis at 30 d post insemination. Data were analyzed using a MIXED procedure of SAS and examined for effects of inseminator, body condition score (BCS), and location and age. Statistical significance was determined at P < 0.05 and a tendency at 0.05< P < 0.10. Age, BCS, and location did not affect (P > 0.05) pregnancy rates. Cows exposed to the presynchronization program tended to have greater AI pregnancy rates compared to cows that did not receive the presynchronization program (57.7±5.3 vs. 46.9±5.3%, respectively; P = 0.0687). AI pregnancy rates were greater in cows with >1 ng/mL P4 compared to cows with < 1 ng/mL P4 at the start of FTAI (77.7±7 vs. 55.7±6.2%, respectively; P = 0.0204). Furthermore, AI pregnancy rates were decreased by inseminator C (26.1±7.4) compared to the other inseminators this breeding season (A-54.4±7.9; B- 62.3±5.3; D-57.8±7.2; and E -51.1±5.2; P = 0.0026). Based on these data, incorporating a presynchronization program to ensure the presence of a CL at the start of a FTAI protocol may improve pregnancy success in postpartum beef cows.