BOVINE SOMATOTROPIN AND CLINICAL MASTITIS - EPIDEMIOLOGIC ASSESSMENT OF THE WELFARE RISK

Published data on clinical mastitis in BST trials are re-evaluated applying general epidemiological methods. Results of pooled analyses are used to estimate relative risks and population attributable fractions. The estimates suggest, that BST treatment is associated with 15-45% excess incidence of clinical mastitis, which is probably due to an indirect causal effect through increased milk yield. The increased risk is of concern to the welfare of future populations of dairy cows. It will limit the acceptability and usage of BST under common management conditions, and it should be taken into account in evaluating BST preparations for marketing authorization.