Evaluation of prostaglandin F2α versus prostaglandin F2α plus gonadotropin-releasing hormone as Presynch methods preceding an Ovsynch in lactating dairy cows: A meta-analysis.

Presynchronization of cows with 2 injections of prostaglandin administered 14 d apart (Presynch-Ovsynch) is a widely adopted procedure to increase pregnancy per artificial insemination (P/AI) at first service. Recently, a presynchronization protocol including GnRH and PGF2α (Double-Ovsynch; GnRH, 7 d, PGF2α, 3 d, GnRH) followed 7 d later by an Ovsynch protocol was introduced to overcome the limitations of PGF2α-based protocols for presynchronization of anovular cows and to precisely set up cows on d 7 of the estrous cycle when the Ovsynch is initiated. A systematic review of the literature and a meta-analytical assessment was performed with the objective to compare the reproductive performance of lactating dairy cows presynchronized with these 2 protocols for the first timed AI (TAI) considering parity-specific effects. A fixed or a random effects meta-analysis was used based on the heterogeneity among the experimental groups. Reproductive outcomes of interest were P/AI measured on d 32 (28-42) and pregnancy loss between d 32 and 60 (42-74) of gestation. A total of 25 articles with 27 experimental groups from 63 herds including 21,046 cows submitted to first TAI using either a Presynch-Ovsynch or a Double-Ovsynch protocol were reviewed. Results for P/AI were then categorized by parity if available. Information was available for P/AI for 7,400 and 10,999 primiparous and multiparous cows, respectively. Information regarding pregnancy loss was available for 7,477 cows. In the random effects model for all cows, the overall proportion of P/AI was 41.7% [95% confidence interval (CI): 39.1-44.3; n = 8,213] and 46.2% (95% CI: 41.9-50.5; n = 12,833) on d 32 after TAI for Presynch-Ovsynch and Double-Ovsynch, respectively. In the random effects model for primiparous cows, the overall proportion of P/AI was 43.4% (95% CI: 36.2-47.7; n = 2,614) and 51.4% (95% CI: 47.4-55.4; n = 4,786) on d 32 after TAI for Presynch-Ovsynch and Double-Ovsynch, respectively. In the random effects model for multiparous cows, the overall proportion of P/AI was 39.2% (95% CI: 36.2-42.3; n = 3,411) and 41.4% (95% CI: 36.4-46.4; n = 7,588) on d 32 after TAI for Presynch-Ovsynch and Double-Ovsynch, respectively. The overall proportion of pregnancy loss was 11.3% (95% CI: 7.6-15.7; n = 3,247) and 11.7% (95% CI: 9.3-14.3; n = 4,230) on d 60 after AI for Presynch-Ovsynch to and Double-Ovsynch, respectively. Substantial heterogeneity existed among the experimental groups regarding P/AI and pregnancy loss. In summary, a benefit was detected for P/AI in primiparous cows presynchronized with a Double-Ovsynch protocol for the first TAI, but this benefit was not observed in multiparous cows.