1115 The 9-d CIDR-PG protocol: Incorporation of prostaglandin pretreatment into a long-term, CIDR-based estrus synchronization protocol improves timed AI pregnancy rates in postpartum suckled beef cows.

An experiment was designed to test the hypothesis that pregnancy rates after fixed-time artificial insemination (FTAI) among postpartum suckled beef cows would be improved by incorporating pretreatment with prostaglandin F2α (PG) into a long-term, CIDR-based estrus synchronization protocol. The 9-d CIDR-PG protocol, a modified protocol in which PG is used to facilitate a decreased length of progestin treatment, was compared to the 14-d CIDR-PG protocol. Protocols were compared on the basis of initial estrus response following CIDR removal, final estrus response following the administration of PG, and pregnancy rate resulting from FTAI. Estrus was synchronized for 321 cows across three locations. Treatments were represented across locations, and cows within each location were randomly assigned to one of the two protocols based on age and body condition score (BCS). Cows assigned to the 14-d CIDR-PG treatment received a CIDR insert (1.38 g progesterone) on d 0 with removal of CIDR on d 14; 25 mg PG 16 d after CIDR removal on d 30; and 100 μg GnRH on d 33, 72 h after PG. Cows assigned the 9-d CIDR-PG treatment received 25 mg PG and a CIDR insert (1.38 g progesterone) on d 5; 25 mg PG and removal of CIDR on d 14; 25 mg PG 16 d after CIDR removal on d 30; and 100 μg GnRH on d 33, 72 h after PG. Estrus response following CIDR removal on d 14 did not differ between treatments (87% versus 85%, P = 0.71), and there was no difference in final estrus response following the administration of PG on d 30 (53% versus 50%, P = 0.69). A significant effect of treatment was found on pregnancy rate resulting from FTAI, with cows assigned to the 9-d CIDR-PG protocol achieving greater FTAI pregnancy rates than cows assigned to the 14-d CIDR-PG protocol (63% versus 53%, P < 0.05). Across treatments, greater pregnancy rates (P = 0.06) tended to be achieved by cows that expressed estrus before FTAI (69% for 9-d CIDR-PG, 57% for 14-d CIDR-PG) than were achieved by cows that failed to express estrus (57% for 9-d CIDR-PG, 48% for 14-d CIDR-PG). In summary, when using a long-term, CIDR-based estrus synchronization protocol among mature, suckled beef cows, FTAI pregnancy rates are improved through use of the 9-d CIDR-PG protocol.