A study of mastitis bacteria and herd management practices to identify their relationship to high somatic cell counts in bulk tank milk.

Thirty dairy herds, selected to cover a wide range of bulk tank somatic cell count (BTSCC) values, were used to study the relationship between the levels of the principal species of mastitis-causing bacteria, herd management practices and the BTSCC. A good correlation was found between the number of mastitis streptococci (Streptococcus agalactiae, S. dysgalactiae and S. uberis) found in bulk tank milk and the BTSCC. Staphylococcus aureus was less significantly correlated to BTSCC, but was of increasing importance in borderline BTSCC herds, where lower excretion levels into milk were unlikely to trigger hygiene penalties and so alert producers to the presence of a significant mastitis problem. High BTSCC herds had significantly lower yields and were less likely to use a post-milking teat dip or to have a regular programme of milking machine maintenance or automatic cluster removal. These herds also tended to buy in replacements rather than breed their own. Overall the management of high BTSCC herds showed less commitment to implementing mastitis control procedures than herds with a consistently low BTSCC.