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Objectives: 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) for the first service. Two different strategies can be observed. Either all cows are time-inseminated (onlyTAI) or cows detected in estrus after the second PGF2α injection are inseminated and the remaining cows without signs of estrus will be subject to TAI (EDAI+TAI). The objective of our study was to evaluate the effect of insemination after estrous detection during a Presynch-Ovsynch protocol for first service on fertility in lactating dairy cows.
Materials and Methods: A systematic review of the literature was performed. Two statistical approaches were conducted using a fixed or a random effects meta-analysis based on the heterogeneity among the experimental groups. Reproductive outcomes of interest were P/AI measured on d 32 (28 to 42) and pregnancy loss between d 32 and 60 (42 to 74) of gestation. In approach 1, 3 randomized controlled studies including 1,689 cows with the primary objective to evaluate the effect of insemination after estrous detection in a Presynch-Ovsynch protocol were used. In approach 2, cows from approach 1 and cohorts from another 17 experimental groups including 8,124 cows submitted to first AI using a Presynch-Ovsynch protocol were used. Information regarding pregnancy loss was available or 5,200 cows.
Results: In approach 1, the incorporation of insemination after estrous detection decreased the odds of pregnancy by 35% (OR = 0.65; 95% CI = 0.53 – 0.80) on d 32 after AI using a fixed effects model. There was no effect on pregnancy loss on d 60 of gestation (OR = 0.88; 95% CI = 0.55 – 1.43). There was no heterogeneity among the 3 studies regarding P/AI and pregnancy loss. In approach 2, the overall proportion of P/AI was 30.9% (95% CI = 26.71 – 35.28; n = 2,400) and 41.7% (95% CI = 39.76 – 42.01; n = 7,413) on d 32 after AI for EDAI+TAI and onlyTAI, respectively. The overall proportion of pregnancy loss was 11.7% (95% CI = 6.11 – 18.8; n = 1,811) and 9.6% (95% CI = 6.37 – 13.33; n = 3,389) on d 60 after AI for EDAI+TAI and only TAI, respectively. There was substantial heterogeneity among the experimental groups regarding P/AI and pregnancy loss.
Conclusions: Based on a meta-analysis considering 20 manuscripts including 27 herds and 9,813 AI we compared 2 different management strategies for first service using a Presynch-Ovsynch protocol. Cows with 100% TAI after completing a Presynch-Ovsynch protocol had more P/AI compared to cows that were inseminated after estrous detection or received TAI for cows showing no signs of estrus. The results of this meta-analysis are based on a large number of herds with different managerial conditions and seem to be applicable to high producing dairy herds under confinement housing.