Effects of repeated episodes of generic clinical mastitis on mortality and culling in dairy cows

Bovine clinical mastitis (CM) can be detrimental to a dairy farm's profitability, not only in terms of lost production and treatment costs, but also because of the loss of the cows themselves. Our objective was to estimate the effects of multiple occurrences of generic bovine CM on mortality and culling. We studied 16,145 lactations from 5 large, high-producing dairy herds, with 3,036 first, 758 second, and 288 third CM cases observed in the first 10 mo after calving. Generalized mixed models, with a random herd effect, were used to quantify the effect of CM on mortality and culling. Other control variables included in the models were parity, stage of lactation, and other diseases. Clinical mastitis in the current month significantly increased mortality in all parities. Among primipara, odds ratios and 95% confidence intervals were 5.6 (1.7, 18.0), 23.3 (7.1, 76.2), and 27.8 (3.7, 209.9) for the first, second, and third CM episode, respectively. Among multipara, respective estimates were 9.9 (7.4, 13.2), 12.0 (8.0, 18.0), and 11.5 (6.1, 21.4). Clinical mastitis significantly increased the risk of a cow being culled for a period of at least 2 mo after any CM case. Our findings provide dairy producers with information on mortality and culling associated with CM cases without considering the causative agent, and can also be used for economic analysis of CM management options.