Estimating the proportion of clinical mastitis attributable to subclinical mastitis in dairy cattle using two multivariable statistical approaches

The aim of this study was to quantify the proportion of first bovine CM cases attributable to high composite somatic cell counts (CSCC). Cows were followed from the first CSCC measurement postpartum until CM or censoring, using survival analysis. A conditional logistic regression model was also fitted to the data with CM cows being matched to cows without CM. Both models identified high CSCC cows to have a higher risk for subsequent CM cases than low CSCC cows. The population attributable fraction was 0.22 for primiparae and 0.17 for multiparae according to the logistic regression model, while it was 0.25 in the survival analysis. The latter approach also identified that the proportion of cows without CM would increase from 89% to 93%. Both multivariable statistical approaches showed that a substantial reduction in CM can be achieved by decreasing the prevalence of high CSCC in the dairy population