Impacts of incorporation of follicle stimulating hormone into an estrous synchronization protocol for timed artificial insemination of crossbred beef cattle

Abstract

One-hundred-eighty crossbred beef cows and 66 crossbred beef heifers across three locations were stratified by body weight (BW), body condition score (BCS), and age (within location) to evaluate administration of follicle stimulating hormone (FSH) on Day 2 using a modified 7-day CO-Synch plus CIDR® protocol (Day 0=CIDR insertion) with timed-artificial insemination (TAI) at 72h (cows) or 54h (heifers) following CIDR removal. Estrous response following CIDR removal was determined using an Estrotect patch and TAI and final pregnancy rates were determined by transrectal ultrasonography 42–45days following TAI and ≥45days following removal of clean-up bulls. Estrous response rate, TAI and final pregnancy rates for cows were not affected (P≥0.65) by treatment. Cows that exhibited estrus had greater (P<0.01) TAI pregnancy rate (66%) than cows not exhibiting estrus (38%). There was an estrous response by postpartum length interaction (P=0.02) where cows exhibiting estrus and ≥55days postpartum had greater TAI pregnancy rates (75%) compared to cows not exhibiting estrus and <55days postpartum (39%) or ≥55days postpartum (28%). For heifers, timed AI (P=0.46) and final pregnancy rates (P=0.45) were similar across treatments and estrous response had no effect (P=0.30) on TAI pregnancy rates. In conclusion, the addition of FSH to the CO-Synch plus CIDR estrous synchronization protocol did not increase TAI pregnancy rates in beef cows or heifers. However, a positive estrous response to the synchronization protocol was associated with increased TAI pregnancy rates in cows.