Association between milk somatic cell counts up to 400,000 cells/ml and clinical mastitis in French Holstein cows

The relationship between somatic cell counts (sccs) up to 400,000 cells/ml in individual cows and clinical mastitis was studied by collecting monthly records for a year from 101 Holstein herds in the west of France. Monthly records obtained after any case of clinical mastitis occurring within the lactation were excluded. The resulting dataset consisted of 29,700 records from 4677 cows. The data were analysed by the logistic regression method. Herd, lactation number, calendar month, milk production, stage of lactation on the day of test, and scc on previous test days were assumed to affect the likelihood of clinical mastitis. There was no significant relationship between scc and the subsequent occurrence of clinical mastitis for an scc up to 100,000 cells/ml, but the risk of clinical mastitis increased as the scc increased up to 400,000 cells/ml. These results suggest that in individual cows, a low scc recorded after five days in milk does not lead to an increased risk of clinical mastitis.