Comparison of 5-day versus 7-day CIDR CO-Synch protocol in crossbred commercial beef cows

Artificial insemination (Al) is used by only approximately 10% of beef producers in the United States. Estrus synchronization and timed AI (TAI) minimize time and labor relative to heat detection; however, these factors are still a big constraint for producers. In literature, conception rates following TAI using various synchronization protocols range from approximately 30 to 65%. One commonly used protocol is CO-Synch, which consists of a shot of GnRH on day 0, a shot of PGF2a on day 7, and another shot of GnRH at breeding (72 hours after PGF2a). Several variations of CO-Synch that minimize labor but maximize conception rate have been identified, and comparisons are ongoing. Although the 7-day CIDR CO-Synch has been used with relative success, recent studies have suggested that a similar 5-day protocol may result in improved conception rates. Although the 5-day protocol may yield higher conception rates, especially in heifers, it also may require a second dose of PGF2a given six hours after CIDR removal, which will significantly increase time and labor required. Several recent studies have compared the 5-day to the 7-day CIDR CO-Synch, but cow numbers were too low to detect small differences. Further comparison of these two protocols is necessary to determine the benefit versus the cost of the 5-day CIDR CO-Synch.