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Split-time AI: Delayed insemination of non-estrous beef cows in timed artificial insemination following the 7-d CO-Synch + CIDR protocol
An experiment was designed to test the hypothesis that pregnancy rates in postpartum beef cows after fixed-time artificial insemination (FTAI) may be improved by delaying insemination of those cows that have not expressed estrus prior to the standard FTAI time. Estrus was synchronized for 951 mature, suckled cows across 9 locations using the 7-d CO-Synch + CIDR protocol (100 μg GnRH + CIDR [1.38 gm progesterone] on d 0; 25 mg PGF2α at CIDR removal on d 7; and 100 μg GnRH on d 10, 66 h after CIDR removal). Estrus detection aids (Estrotect) were applied at PGF2α and CIDR removal on d 7, and estrous expression was recorded at GnRH on d 10. Treatments were equally represented across locations, and cows within each location were assigned to one of two treatments based on age, days postpartum (DPP), and body condition score (BCS): (1) FTAI (concurrent with GnRH, 66 h after PGF2α) regardless of estrous expression prior to GnRH, or (2) FTAI for cows having expressed estrus, and delayed AI (20 h after GnRH) for cows failing to express estrus. In both treatments, cows that expressed estrus prior to FTAI achieved higher pregnancy rates than cows that did not (P < .0001). However, no significant effect of treatment was found on AI pregnancy rate (P = .757). In summary, mature suckled beef cows may be successfully artificially inseminated using a strategy of “split-time” AI: insemination at the standard time of 66 h after PGF2α for cows that have expressed estrus and delayed insemination at 20 h after GnRH for cows that have not expressed estrus prior to the standard AI time in the 7-d CO-Synch + CIDR protocol. However, such a strategy does not appear to offer a significant improvement in pregnancy rates compared to a standard FTAI approach.
Keywords:
artificial insemination
estrus synchronization
beef cow