The effect of udder infection on the bacterial flora of the bulk milk of ten dairy herds

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Abstract
The significance of udder infection as a factor increasing the bacterial count of herd bulk milk was measured monthly for 1 yr in 10 dairy herds in Southern England. Staphylococcus aureus or mastitis streptococci were detected in 86% of samples, usually in numbers between 1000-10,000 cfu [colony-forming units]/ml of milk. In 8 and 2% of samples, respectively, > 20,000 or 100,000 cfu of mastitis pathogens/ml of milk were detected. This occurred most commonly in the herds with a high incidence of Streptococcus uberis mastitis. The total bacterial counts of the herds'' milks varied between 13,960-46,230 cfu/ml in the winter and between 6510-63,000 cfu/ml in the summer. No correlation was found between bacteriological quality of herd milk and the cleanliness of the milking machine and pipeline as assessed by plant rinses.