Comparison of a Select Synch/CIDR + Timed Artificial Insemination vs a Modified Co-Synch/CIDR Estrous Synchronization Protocol in Suckled Bos Indicus Х Bos Taurus Cows

Suckled Bos indicus  Bos taurus cows were used to compare a Select Synch/CIDR + timed artificial insemination (AI) protocol (SSC) vs a modified Co-Synch/CIDR protocol (COS). Five groups of suckled Bos indicus  Bos taurus cows were evaluated (n=659). Cows received GnRH and a CIDR on d 0. On d 7, SSC cows had their CIDR removed and received prostaglandin F2α (PGF2α), whereas COS cows had their CIDR removed and received PGF2α on d 7.5. Estrus was detected for 3 d following PGF2α and SSC cows were AI 8 to 12 h after observed in estrus. Cows on the SSC protocol not exhibiting estrus by 72 h after PGF2α were timed-AI between 76 to 80 h and received GnRH. Estrus was detected on COS cows, but all COS cows were timed-AI at 66 h after PGF2α and received GnRH, regardless of whether they displayed estrus or not. Similar (P>0.05) synchronized pregnancy rates were achieved with the SSC (49.4%; 164/332) and COS (47.1%; 154/327) protocols. Differences (P<0.05) in estrous response, timed-AI pregnancy, and synchronized pregnancy rates were observed between groups. Days postpartum influenced (P<0.05) timed-AI pregnancy and synchronized pregnancy rates, with longer postpartum cows achieving greater pregnancy rates. Cycling status did not (P>0.05) influence synchronized pregnancy rates. In summary, this field trial suggests that similar pregnancy rates can be achieved using a straight timed-AI synchronization protocol (COS) compared to a heat detection + cleanup timed-AI protocol (SSC).