Effects of a Timed Insemination Following Synchronization of Ovulation Using the Ovsynch or CO-Synch Protocol in Beef Cows

Abstract

This study compared pregnancy rates of suckled beef cows that were time inseminated following synchronization of ovulation using the Ovsynch protocol. Multiparous beef cows (n=771) within each of three locations were stratified by breed type, age, postpartum interval, and AI sire, and randomly allotted to receive either the Ovsynch or CO-Synch protocol. The Ovsynch protocol consisted of an injection of GnRH (100 μg) on d 0, an injection of PGF2α on d 7, another injection of GnRH (100 μg) on d 9, and timed insemination on d 10. The CO-Synch protocol consisted of the same hormone injection schedule as the Ovsynch protocol, but cows were time inseminated on d 9, when the second GnRH injection was administered. Pregnancy rates did not differ between treatments at each location (P>0.1). However, when data were pooled across location, pregnancy rate was higher (P=0.02) for cows that received the Ovsynch protocol (57%) than for cows that received the CO-Synch protocol (49%). No difference (P>0.1) in pregnancy rate due to cow age, postpartum interval, body condition score, age by treatment, or postpartum interval by treatment was detected among pooled data. Among cows with a body condition score of 6.0 or greater, pregnancy rates were higher (P=0.04) for Ovsynch treated cows (72%) than for CO-Synch treated cows (53%). These data demonstrate that the Ovsynch and CO-Synch protocols result in acceptable pregnancy rates to a timed insemination in beef cows. Whether the increase in pregnancy rates obtained using the Ovsynch protocol will warrant handling cows a fourth time for insemination will likely vary by management intensity.