Efficacy of the 5 Day CO-Synch Estrous Synchronization Protocol with or Without the Inclusion of a Controlled Internal Drug Release Device in Beef Cows

To increase utilization of artificial insemination by beef producers, estrous and ovulation synchronization protocols must be re-evaluated in an attempt to reduce labor, cost, number of handlings, or a combination thereof without negatively impacting pregnancy rates. One potential way to reduce cost in these systems is through the strategic removal of hormones, such as the controlled internal drug release device (CIDR), from the protocol. While this concept has been tested in a 7 day synchronization protocol, it has not been evaluated in the newer 5 day synchronization protocols. The objective of this study was to compare TAI and overall breeding season pregnancy rates in primiparous and multiparous cows synchronized with the 5 d CO-Synch protocol with or without the inclusion of a CIDR. We hypothesized that use of a CIDR would improve timed-artificial insemination (TAI) and overall breeding season pregnancy rates. Results from this study indicate that while overall breeding season pregnancy rates are not impacted by removal of a CIDR in a 5 d CO-Synch protocol (90.3%; P = 0.94), TAI conception rates are improved when a CIDR insert is utilized (62.3 vs. 50.7%; P < 0.001). Based on these data, use of a CIDR in the 5 d CO-Synch program is still recommended to optimize pregnancy success in an AI management system.