Use of an enzyme-linked immunosorbent assay to monitor the control of Staphylococcus aureus mastitis.

Conventional culture methods were used to evaluate the ability of an ELISA to identify Staphylococcus aureus IMI. The test was 96% accurate; sensitivity was 90%, and specificity was 97%. The test was used to screen preserved milk samples rapidly in 10 cooperator herds. Prevalence of IMI was greater than 10% in 6 herds at the first test. Average prevalence of cows scoring +2 (suspect) and +3 (positive) was 12.6%. Prevalence declined during the 12-mo study. Incidence of new IMI decreased from 7.9% at 6 mo to 3.6% at 12 mo. Rinsing teat cup liners with a 25-ppm iodophor or 100-ppm chlorine solution reduced the presence of S. aureus on the milking machine liners by 97%. Elevated scores were correlated with increases in lactation number. Milk antibody concentrations changed quadratically with increasing SCC. The SCC increased as milk antibody concentration increased. In 38 dairy herds, bulk tank antibody tests reflected herd prevalence of S. aureus infection. The average prevalence was 15.0% in 87 herds in which all lactating cows were tested.