Segregation or use of separate milking units for cows infected with Staphylococcus aureus reduced prevalence of infection and bulk tank somatic cell counts

Abstract

Dairy herds (n = 76) with initial prevalence of Staphylococcus aureus IMI> 10% were included in this study, from among approximately 2800 herds visited between January 1992 and July 1994 by the Quality Milk Promotion Services at Cornell University. The farms were located in New York and Pennsylvania. Other inclusion criteria were that herds did not change teat dipping or dry cow treatment practices, were not segregating cows that were positive for S. aureus at the initial visit, and did not cull > 50% of those found positive on the initial visit. Paired t tests and Wilcoxon rank sum tests were methods of statistical analysis. Mean herd size was 59 lactating cows, and herd size ranged from 28 to 436 cows. Percentage of herds teat dipping, using dry cow treatment, and mean herd size were not different among segregation groups. Mean number of visits (3.5 per herd) did not differ among groups. During a follow-up period (6-to-24 mo), segregation or separate milking of cows (n=21 herds) that were positive for S. aureus resulted in reduction of 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 (n=55 herds) not segregating S. aureus cows, 22.5 to 20.2%, and the change in SCC from 698,000 to 484,000 for nonsegregated herds was less of a reduction than for the segregating herds. Segregation or use of separate units for cows known to be positive for S. aureus is an effective mastitis control practice.