Extending the Interval from Presynch to Initiation of Ovsynch in a Presynch-Ovsynch Protocol did not Reduce Fertility of Lactating Dairy Cows Not Detected in Estrus that Received Timed Artificial Insemination
Our objective was to determine if extending the interval from Presynch to initiation of Ovsynch by 2 d (from 12 to 14) in a Presynch-Ovsynch protocol would reduce pregnancies per AI (P/AI) for cows not detected in estrus that receive timed AI (TAI). Lactating dairy cows (n = 1817) from 4 commercial farms in New York (Farm A=218, B=1,031, C=258, and D=310) were enrolled in the Presynch-Ovsynch protocol to receive TAI at 73 ± 3 DIM. Cows were blocked by parity and randomly assigned to two groups: PS12 (n=909; PGF-14d-PGF-12d-Ovsynch-56) or PS14 (n=908; PGF-14d-PGF-14d-Ovsynch-56). Timed AI was performed approximately 16 h after GnRH. Cows detected in estrus at any time from the second PGF injection of Presynch until the day before TAI were inseminated. Pregnancy was assessed at 39 ± 3 d after AI using transrectal ultrasound. The percentage of cows receiving TAI was greater (P<0.001) for PS14 than PS12 (55.2 vs. 48.5% respectively), was greater (P<0.001) for farm D (70.7%) than A (60.1%) and C (57.8%) whereas farm B (43.0%) had the lowest percentage of cows receiving TAI. More (P<0.001) multiparous (58.4%; 661/1131) than primiparous (41.0%; 281/686) cows received TAI. There was no treatment by farm interaction (P=0.74) or treatment by parity interaction (P=0.96) for the percentage of cows receiving TAI. Pregnancies per AI for cows receiving AI after detection of estrus was similar (P=0.41) for PS12 and PS14 (34.6 vs. 37.4% respectively), was not affected (P = 0.44) by farm, and was similar (P = 0.36) for primiparous and multiparous cows (37.5 vs. 34.5% respectively). Pregnancies per AI for cows receiving TAI after completing the Presynch-Ovsynch protocol were similar (P=0.98) for PS12 and PS14 [35.4 (156/441) vs. 35.5% (178/501), respectively], tended to differ by farm (P=0.10), and were similar (P=0.50) for primiparous and multiparous cows (37.1 vs. 34.8% respectively). Also, there was no treatment by farm (P=0.91) or treatment by parity interaction (P=0.34) for P/AI after TAI. Thus, extending the interval from the second PGF injection of Presynch to the initiation of the Ovsynch protocol by 2 d (from 12 to 14 d) did not reduce fertility of lactating dairy cows that were not detected in estrus and completed Presynch-Ovsynch to receive TAI.
Presynch-Ovsynch, timed AI, dairy cow