Influence of Numbers of Post-calving Days, Parity, and Season on Reproductive Performance in Anestrous Dairy Cows after OVSYNCH/Timed Artificial Insemination

The aim of this study is to assess reproductive performance in dairy cows after OVSYNCH/Timed Artificial Insemination (OVSYNCH/TAI) protocol and to determine whether numbers of post-calving days, parity, and season affect it. Subjects were 556 Holstein dairy cows from 24 herds. The cows had either not been observed to be estrous after calving or had not conceived upon artificial insemination (AI) before being subjected to OVSYNCH/TAI. Of the 556 cows, 41 (7.4%) were in heat between the initial GnRH injection and PGF2α, 7 days later. Most of them were observed to be in estrus 6-7 days after GnRH. Of these 41 cows, 16 were artificially inseminated at this heat; and 5 (31.3%) conceived. A total of 513 cows was inseminated artificially at fixed times after OVSYNCH. The conception rate for this timed-AI was 55.4%. No effects caused by numbers of post-calving days, parity, and season were observed. In conclusion, du ing the OVSYNCH protocol, about 7% of the animals subjected to the procedure can be observed to be in estrus; and numbers of post-calving days, parity, and season exert no effect on conception rates after OVSYNCH/TAI.