INCIDENCE OF CLINICAL MASTITIS IN A RANDOM SAMPLE OF DAIRY HERDS IN THE SOUTHERN NETHERLANDS

The incidence of clinical mastitis and distribution of pathogens in da iry cows was estimated in 171 randomly selected dairy herds in the sou thern Netherlands. A total of 1103 quarter cases were reported. The av erage annual incidence rate was 12.7 quarter cases per 100 cows per ye ar. The most frequent isolates from clinical cases were Escherichia co li (16.9 per cent), Staphylococcus aureus (14.4 per cent), Streptococc us uberis (11.9 per cent) and Streptococcus dysgalactiae (8.9 per cent ). Most cases were reported in early lactation: 25.4 per cent in the f irst month of lactation for all cows, and 39.1 per cent in the first m onth for first lactation cows. The rear quarters had a significantly h igher incidence rate than the front quarters, Cows with an E coli infe ction showed more general clinical signs than cows infected with S aur eus, S uberis and S dysgalactiae. A significantly higher incidence was observed in herds with a low (<150,000 cells/ml) bulk milk somatic ce ll count than in herds with a count above 250,000 cells/ml.