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 72 h (cows) or 54 h (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 42–45 days following TAI and ≥45 days 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 ≥55 days postpartum had greater TAI pregnancy rates (75%) compared to cows not exhibiting estrus and