Segregation or use of separate milking units for cows infected with Staphylococcus aureus: effects on prevalence of infection and bulk tank somatic cell count

Dairy herds (n = 76) with an initial prevalence of Staphylococcus aureus IMI > or = 10% were included in this study. Criteria were that herds did not change teat dipping or dry cow treatment practices, did not segregate cows that were positive for S. aureus at the initial visit, and did not cull > 50% of cows found to be positive on the initial visit. During a follow-up period (6 to 24 mo), segregation or separate milking of cows that were positive for S. aureus reduced prevalence from 29.5 to 16.3% and bulk tank SCC from 600,000 to 345,000/ml. Prevalence of S. aureus mastitis was unchanged for herds that did not segregate cows with S. aureus, 22.5 to 20.2%, and the reduction in SCC from 698,000 to 484,000 for nonsegregated herds was also smaller. Segregation of cows that were known to be positive for S. aureus is an effective mastitis control practice.