Comparison of 2 estrous synchronization protocols for use with X-sorted semen in lactating beef cows

A study investigated whether prostaglandin injection on d 7 of a modified 14-d progesterone protocol improved estrous response in beef cows, and the effect of insemination timing on conception rate when using X-sorted semen. Treatment 1 (control; n = 132) cows received a CIDR progesterone insert from d 0 to 14, gonadorelin treatment on d 16, and prostaglandin F2α treatment on d 23. Treatment 2 (n  = 132) cows received the same synchronization treatment, except an additional dose of prostaglandin F2α was given on d 7 of CIDR treatment. Cows were observed for estrus over an 84-h period and inseminated with X-sorted semen either 9 to 15 h or 16 to 24 h after detected estrus, followed 10 d later by exposure to fertile bulls for 45 d. Percentage of cows exhibiting estrus did not differ (P = 0.33) at 76.5 and 71.2% for treatments 1 and 2, respectively. Conception rates after AI with X-sorted semen were similar (P = 0.64) at 63.3 and 66.7% for treatments 1 and 2, respectively. Time of insemination had no effect (P = 0.72) on conception rate. At the end of the breeding season, overall pregnancy rates were also similar (P = 0.74) at 83.3 and 84.9% for cows in treatments 1 and 2, respectively. Results demonstrated no benefit to addition of prostaglandin F2α on d 7 to the estrous synchronization protocol and that acceptable conception rates can be achieved in lactating beef cows when using X-sorted semen over a range of insemination times.