The Effect of Second Prostaglandin F2α Application with the Presynchronization Protocol on Fertility in Simmental Cows

The objective of the study was to evaluate the effect of an additional PGF2α injection 24 hours after the first PGF2α in the timed AI Ovsynch protocol on the pregnancy/artificial insemination (P/AI) rate of Simmental cows presynchronized with PG-3-G. The study was conducted on a commercial farm with 103, lactating Simmental cows. Animals were randomly divided into two groups (1) PG-3-G Group (n=56): PGF2α on day 0; GnRH on day 3; Ovsynch initiation after on day 10. (2) PG-3-PG Group (n=47): Second PGF2αaddition 24 hours apart before timed AI to PG-3-G protocol. Parity, milk yield, and days in milk (DIM) were compared between the synchronization protocols. The pregnancy rates in the postpartum first and ≥2 TAI were similar between groups (p=0.462 and p=0.566, respectively). There were no statistical differences in the P/AI rates between groups 51.78% (29/56) and 51.06% (27/47), respectively. Multiparous cows revealed numerically higher pregnancy rates than the primiparous cows. However, P/AI results did not differ between groups (p=0.942). The mean preovulatory follicle diameter was 1.71±0.15 cm in the PG-3-G group, and 1.79±0.15 cm in the PG-3-PG group and the difference between groups was significant (p=0.047). In conclusion, administration of a second PGF2α injection to the protocol improved the P/AI numerically in multiparous cows, and preovulatory follicle size. Nevertheless, those findings need to be evaluated by conductinga larger study with a larger sample size.