Comparison of Pregnancy Rates after Timed Artificial Insemination in Ovsynch, Heatsynch and CIDR-Based Synchronization Protocol in Dairy Cows

The objective of this study was to compare the effects of three different estrus synchronization protocols on the pregnancy rates of lactating dairy cows. Group 1 (Ovsynch protocol; n= ) animals received 20 μg GnRH on day 0, 500 μg PGF2α on day 7 and 20 μg GnRH on day 9; Group 2 (Heatsynch protocol; n= ) received 20 μg GnRH on day 0, 500 μg PGF2α on day 7 and an injection of 1 ml estradiol cypionate i.m. on day 8; Group 3 (CIDR protocol; n= ) an intravaginal CIDR insertion on day 0, inject with 500 μg PGF2α on day 6, and removed CIDR on day 7. All animals were fixed-time artificial inseminated (FTAI) on day 10. Pregnancy diagnosis was performed on all animals via transrectal ultrasonography at 35±3 days following FTAI. Estrus activity observed in the Heatsynch group animals was higher than that in the Ovsynch and CIDR-based groups (P<0.05). There were significant differences among groups for vaginal electrical resistance in days 7 and 10 (P<0.05), but there was no significant difference among groups on first and second service pregnancy rates (P>0.05). In conclusion, these three synchronization protocols providing satisfactory pregnancy rates in lactating dairy cows can be equally usable.