Comparison of electrical conductivity of milk with other indirect methods for detection of subclinical mastitis.

Efficacy of detecting subclinical mastitis by electrical conductivity of milk was compared with that of other indirect methods including chloride, sodium, potassium, lactose, bovine serum albumin, and somatic cell count of milk. Quarter samples of foremilk, strippings, and bucket milk were obtained from 75 cows at the afternoon milking over 8 wk. Infection of quarters was ascertained by bacteriological analysis. Electrical conductivity, chloride, and sodium content of milk were more accurate for predicting infection status of quarters than were other variables. Most variables were more accurate in predicting infection when measures were in strippings rather than in foremilk or bucket milk. For measures in strippings, misclassifications by electrical conductivity were 11.2 and 15.5% for false positives and false negatives. The accuracy of the electrical conductivity of milk for detection of subclinical mastitis compared favorably with all indirect methods. Accuracy of detection and adaptability to both manual and automatic cow-side mastitis detection systems indicate that the method has considerable potential as a screening test for subclinical mastitis.