[Pathology and productivity of the lactating cow: interrelations based on the level of lactation].

The effects of sanitary problems in dairy herds on milk production have been determined using 595 cases of health problems noted in Friesian and Montbeliarde cows in a long-term feeding trial, covering over 487 lactations. Relationships between each sanitary condition and lactation characteristics were established. On a short-term basis (5 weeks), the greater milk losses were first due to lameness at turnout (56 kg) and second to winter mastitis (24 kg); the effects of lameness lasted beyond the 5th week depending on when the problem was first detected. Over the whole lactation cycle, the highest milk losses resulted from recurrent lameness: 640 kg loss for cows presenting a lameness at least three times, versus 20 kg for those presenting only one lameness. The frequency of recurrent lameness was three times higher in Friesian than in Montbeliarde cows and four times higher with grass silage-based diets as compared with hay diets. Four main types of lactation cycles were characterized on the basis of the cows' level of production, their health status, their reproduction performances and their culling rate. Cumulative differences in any of those characteristics accounted for up to a 1 800 kg difference in milk production.