Pregnancy outcome of lactating dairy cows assigned for Presynch-Ovsynch synchronization program and inseminated either at detected standing heat or at scheduled fixed time

Objective: To determine if insemination at standing heat results in a similar or higher pregnancy rate compared with fixed time artificial insemination, and to study some factors affecting the pregnancy rate.Methods: A total of 8 944 inseminations were included in this study, from which 6 823 inseminations were done in Holstein cows and 2 121 inseminations were performed in Simmental cows. All cows were subjected to a Presynch-Ovsynch protocol. Cows detected in estrus (n=7 424) were artificially inseminated, whereas cows not observed in estrus (n=1 520) were submitted to fixed time artificial insemination.Results: The overall pregnancy rate of cows inseminated on the basis of the detected standing heat was comparable to that recorded for cows receiving fixed time artificial insemination. A higher pregnancy rate was recorded for cows during cold months than that recorded during hot months (P=0.000). A higher pregnancy rate was recorded for Simmental compared with that recorded for Holstein cows (P=0.001). Regarding parity, significant differences in the pregnancy rate were detected between primiparous and multiparous cows (P=0.040). In addition, artificial insemination technicians had no sigificant effect on pregnancy rate (P>0.05). Meanwhile, the used artificial insemination sires significantly (P=0.000) impacted the pregnancy rate.Conclusions: Insemination of cows detected in standing heat prior to predetermined fixed time results in similar pregnancy outcome and decreases days to the first service compared with insemination at the scheduled fixed time at the end of the Presynch-Ovsynch synchronization program. The overall pregnancy outcome is not affected by the breeding program, but it is highly impacted by cow’s breed, parity, artificial insemination sire and breeding season.