Sensitivity and specificity of somatic cell count and California Mastitis Test for identifying intramammary infection in early lactation

Associations between values for the somatic cell count (SCC) or the Califor nia Mastitis Test (CMT) and intramammary infection (IMI) were studied in 13 1 dairy cows from three herds during the first 10 d postcalving. Intramamma ry infection was defined as the presence of one or two bacterial species in one or both quarter milk samples taken within 12 h of calving and at d 3 p ostcalving. Quarter milk samples identified IMI in 36% of glands. Values fo r SCC declined at a significantly faster rate over the first 10 d postcalvi ng in noninfected quarters than in infected quarters. The usefulness of qua rter milk SCC and CMT for screening was evaluated by calculating the sensit ivity and specificity for various threshold values and days postcalving. A SCC threshold of 100,000 cells/ml for quarter samples evaluated on d 5 post calving had the maximal sensitivity and specificity for detecting IMI. Eval uation of the CMT samples taken on d 3 postcalving using a threshold reacti on of greater than zero had the highest sensitivity and specificity for det ecting IMI. With this CMT sampling scheme, the sensitivities for detecting IMI with any pathogen, IMI with a major pathogen, and IMI with a minor path ogen were 56.7, 66.7, and 49.5, respectively. The CMT could have a useful r ole in dairy herd monitoring programs as a screening test to detect fresh c ows with IMI caused by major pathogens.