Effect of 2 ovulation synchronization protocols on reproductive performance of May-calving cows

A 2-yr experiment was conducted using Red Angus × Simmental cows (yr 1, n = 145; yr 2, n = 162). Cows were randomly assigned to 1 of 2 treatments: (1) cows received gonadotropin-releasing hormone (GnRH; 100 μg, i.m.) on d 0, prostaglandin F2α (PGF2α; 25 mg, i.m.) on d 7, and GnRH (100 μg, i.m.) with fixed-time AI (TAI) 48 h after PGF2α (CO-Synch); or (2) cows received GnRH (100 μg, i.m.) and controlled internal drug release device (CIDR) insertion on d 0, PGF2α (25 mg, i.m.) and CIDR removal on d 7, and GnRH (100 μg, i.m.) with TAI 60 h after PGF2α (CO-Synch + CIDR). Five days after TAI, bulls were placed with cows for 45 d. Cows synchronized with the CO-Synch + CIDR protocol had increased (P < 0.01) AI and overall pregnancy rates compared with cows synchronized utilizing the CO-Synch protocol. Due to increased AI pregnancy rates, CO-Synch + CIDR cows calved 5 d (± 1 d) earlier (P < 0.01), resulting in a greater (P < 0.01) proportion of cows calving within the first 21 d of the calving season compared with CO-Synch cows. Calf crop weaned per cow exposed was increased (P = 0.02) for CO-Synch + CIDR. Weaning BW per cow exposed was also greater (P = 0.04) for CO-Synch + CIDR. In conclusion, pregnancy rates were greater for CO-Synch + CIDR compared with the CO-Synch synchronization protocol, resulting in more calves born earlier in the calving season and a $55.22/cow increased net return utilizing the CO-Synch + CIDR protocol.