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Short communication: Effect of adding a second prostaglandin F2α injection during the Ovsynch protocol on luteal regression and fertility in lactating dairy cows: A meta-analysis.

Incomplete luteal regression after treatment with a single dose of prostaglandin F2α during an Ovsynch protocol decreases fertility to timed artificial insemination (TAI). To increase the proportion of cows with complete luteal regression and subsequently pregnancy per artificial insemination (P/AI), an additional treatment with PGF2α 24 h after the first has been recommended. A systematic review of the literature and meta-analytical assessment were performed with the objective of evaluating the effects of adding a second PGF2α treatment during the Ovsynch protocol on luteal regression and reproductive performance in lactating dairy cows. Based on the heterogeneity among the experimental treatments, a fixed or a random effects meta-analysis was conducted. Reproductive outcomes of interest were luteal regression at the end of the Ovsynch protocol, and P/AI measured 32 to 39 d after TAI. Seven randomized controlled experiments from 6 published manuscripts including 5,356 cows with the primary objective to evaluate the effect of an additional treatment with PGF2α during the Ovsynch protocol on P/AI were used. Information regarding luteal regression at the end of the Ovsynch protocol was available for 1,856 cows. Adding a second PGF2α treatment on d 8 during the Ovsynch protocol increased the relative risk (RR) of complete luteal regression at the end of the Ovsynch protocol (RR = 1.14; 95% confidence interval = 1.10 to 1.17) using a fixed effects model and the RR for pregnancy (RR = 1.14; 95% confidence interval = 1.06 to 1.22) 32 d after TAI using a fixed effects model. No heterogeneity was observed among the 6 manuscripts regarding complete luteal regression and P/AI. In summary, there was a clear benefit of an additional PGF2α treatment during the Ovsynch protocol on luteal regression (+11.6 percentage units) and on P/AI (+4.6 percentage units).