A meta-analysis of the mastitis vaccination efficacy in dairy cattle

BACKGROUND: Mastitis is the most important disease in dairy cattle with impact in welfare of animals and the economy of the dairy farming activity. Attempts have been made to produce vaccines to prevent the disease, however, results have been dubious. AIM: The aim of this study was to evaluate the efficacy of the mastitis vaccination in dairy cattle by merging several trials to allow evidence synthesis. METHODS: A list of publications with common methodological grounds was selected to allow a quantitative comparison in a meta-analysis with moderators. RESULTS: A mixed methods model (p < 0.001), with four significant moderators was successfully fitted: “year of publication” (p < 0.001), “vaccination timing” (p < 0.01), “type of animal” (p < 0.001), and “vaccine fabrication” (p < 0.001). The model is homogeneous (p > 0.05), with the moderators explaining the variability. Efficacy decreases over time. Vaccines applied after calving show inefficacy [log risk ratio (RR) 1.72 (1.34, 2.21)], and applied before calving show reduced efficacy [log RR 0.86 (0.72, 1.03)]. Commercial vaccines don’t show efficacy [log RR 1.07 (0.94, 1.22)]. Self-fabricated vaccines show efficacy [log RR (0.51, 0.94)]. CONCLUSION: Full clarification of efficacy is not shown; however, if vaccination is used, must follow a pre-calving protocol. While not showing efficacy, the vaccination has demonstrated a reduction of the severity in clinical cases, rate of culling, and has increased the production of milk and milk solids. Vaccination may improve health and welfare but does not prevent the disease effectively; it must be seen as an additional tool to the traditional preventive measures.