Effect of segregation on prevention of intramammary infections by Staphylococcus aureus.

Effectiveness of segregating cows with Staphylococcus aureus intramammary infections was studied over 1 yr. Nine herds were split into control (n = 5) or segregated (n = 4) groups. Cows with S. aureus intramammary infections were milked last in segregated herds. Monthly milk samples were collected aseptically for microbiologic analysis. Mean incidences of S. aureus intramammary infections were 3.7 and 4.3 cases/100 cow-mo in segregated and control herds. The mean prevalence of S. aureus intramammary infections decreased in both segregated and control herds during the study. Mean percentages of cows with S. aureus intramammary infections at the beginning and end of the study were 33.7 and 21.5 in segregated herds and 25.3 and 15.0 in control herds. Cows in all herds with S. aureus intramammary infections were preferentially culled. There were no significant differences in incidence and prevalence of S. aureus intramammary infections between groups, suggesting that S. aureus intramammary infections can be controlled without segregation.