Factors affecting the distribution of clinical mastitis among udder quarters in French dairy cows.

Factors related to the distribution of clinical bovine mastitis between rear and front quarters were studied using data from a 4 year survey of commercial dairy herds in western France. The study involved 844 mastitis cases affecting 597 lactations of 500 French Friesian cows from 44 herds. Risk factor hypotheses were related to certain aspects of lactation, udder conformation and management practices. Distribution was modelled using a hierarchical logistic regression. Rear quarters were affected in 61.9% of cases. The only significant risk factor was the cow's parity; rear quarter clinical mastitis was more frequent in primiparous than in multiparous cows. In this retrospective study, udder conformation did not seem to play a significant role in mastitis distribution. No overdispersion parameter was observed, indicating that each mastitis case could be considered as an independent event.