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

Abstract

<h2>ABSTRACT</h2> 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; 100μg, i.m.) on d 0, prostaglandin F_2α (PGF_2α; 25mg, i.m.) on d 7, and GnRH (100μg, i.m.) with fixed-time AI (TAI) 48h after PGF_2α (CO-Synch); or (2) cows received GnRH (100μg, i.m.) and controlled internal drug release device (CIDR) insertion on d 0, PGF_2α (25mg, i.m.) and CIDR removal on d 7, and GnRH (100μg, i.m.) with TAI 60h after PGF_2α (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.