Use of a CIDR in the 5-day CO-Synch estrous synchronization protocol improves pregnancy rates to timed artificial insemination
The objective of this experiment was to compare timed-AI (TAI) pregnancy rates in suckled beef cows synchronized with the 5 d CO-Synch protocol with (5CIDR) or without (5NoCIDR) the inclusion of an EAZI-BREEDTM CIDR® insert (CIDR). The experiment was conducted in 879 cows over 2 years, and at 3 locations with a total of 5 replications. Cows were assigned to either the 5CIDR (n = 438) or 5NoCIDR (n = 436) protocol by breed, age, and days postpartum. Blood samples were collected to determine estrous cyclicity status for 4 of 5 replications. On d 0 all cows received GnRH (100 µg) and cows in the 5CIDR treatment received a CIDR. On d 5 CIDR were removed (5CIDR) and all cows received 2 separate doses of PGF2α (25 mg/dose) between 2 and 10 h apart. Cows were TAI 72 h after CIDR removal (d 8), concurrent with GnRH (100 µg). Timed-AI and breeding season pregnancy rates were determined via ultrasonography 32 to 38 d after TAI and end of the breeding season, respectively. Data were analyzed with the GLMIIX procedure of SAS. There were no significant treatment-based interactions with year, age, or cyclic status; therefore data were pooled across year and cyclic status. In reps that had cyclicity determined, the proportion of cyclic cows was 89.3% (583/653). Timed-AI pregnancy rates were greater (P = 0.0002) in 5CIDR (62.3%, n = 438) than 5NoCIDR (50.7%, n = 436) treatment. Age classification, year, and cyclicity did not affect TAI pregnancy rates (P ≥ 0.33). In conclusion, to optimize TAI pregnancy rates in beef cows synchronized with the 5 d CO-Synch protocol, the inclusion of a CIDR is recommended.
5 day CO-Synch, Beef cow, CIDR