A method for describing disease patterns during the life span of dairy cows.

This study presents some guidelines for describing the health status of dairy cows over their entire life span. It aims to define some types of health-paths (trajectories) described in terms of disease patterns (at the lactation level) and related to cow characteristics (breed, production potential) and farms. The data were collected over a 20-year period on three experimental farms. Eight diseases were analysed: clinical mastitis, lameness, placental retention, foot rot, digestive disorders, milk fever, metritis, and arthritis. The statistical procedures used were correspondence analysis of time-indexed tables and hierarchical ascending clustering. A total of 28 health-paths were identified and 16 of these (the most common) are described in detail. At the lactation level, eight disease patterns were defined: high incidence of disease other than mastitis (1), predominantly mastitis plus milk fever (2), predominantly foot rot (3), very low incidence of disease (4), mastitis plus digestive disorders (5), very high mastitis incidence (6), low incidence of disease (7), foot rot plus digestive disorders (8). Disease patterns 3 and 6 were more common in shorter life spans (< or = 4 lactations). Conversely, health profiles 2 and 4 were generally related to the longest life spans. These results will be included in a future model of the life span of dairy cows which will also take into account other performance parameters such as milk production and reproduction.