Does the Use of a Sanitary Sheath During Artificial Insemination Improve Pregnancy Outcomes in Cattle? A Systematic Review With Meta-Analysis.

Sanitary sheaths (SS), used to reduce reproductive-tract contamination during bovine artificial insemination (AI), have shown inconsistent associations with pregnancy per AI (P/AI). This systematic review with meta-analysis evaluated whether SS use improves P/AI compared with AI without SS. The primary analysis comprised six independent cohorts contributing seven P/AI strata and 11,367 inseminations. Risk ratios (RRs) were pooled using random-effects models with restricted maximum likelihood estimation and Hartung-Knapp adjustment. The use of SS did not significantly improve P/AI (RR = 1.07; 95% CI: 0.94-1.21; p = 0.245), although the point estimate corresponded to approximately 3.5 additional pregnancies per 100 inseminations. Heterogeneity was moderate (I2 = 43.7%), and the 95% prediction interval crossed the null (RR 0.83-1.36), indicating that the effect may vary across production settings. Sensitivity analyses did not provide robust evidence of benefit: point estimates ranged from RR 1.07 to 1.10, statistical significance depended on dataset composition, and all prediction intervals crossed the null. Exploratory subgroup analyses showed no evidence that the effect differed by AI method, production system, or protective-sheath type. Overall, current evidence does not demonstrate that SS use improves bovine P/AI and does not support its routine use as an effective fertility-enhancing intervention; any potential benefit, if present, may be restricted to sanitary and management conditions that remain insufficiently characterised. Future adequately powered randomised trials are needed to determine whether reducing contamination through SS use causally improves fertility.