Differential cell count as an alternative method to diagnose dairy cow mastitis

Changes in relative cell proportions occurring in diseased mammary glands of dairy cows can be determined using differential cell count (DCC). The present study was carried out in 2 consecutive trials, with 2 goals: (a) to test the consistency of DCC results on subsequent days, and (b) to establish an effective cutoff value for the diagnosis of mastitis. In the first trial, quarter milk and blood samples were taken from 8 healthy cows for 5 consecutive days. Milk samples were tested by somatic cell count (SCC) and bacteriological analysis, and DCC was performed on blood and milk samples by flow cytometer. In the second trial, 16 animals were randomly selected from a different herd and quarter milk samples taken on 3 consecutive milkings. All samples were cyto-bacteriologically analyzed and DCC was performed on the second sampling. In the first trial, mean SCC was 77,770 cells/mL and 4 samples were bacteriologically positive. No fixed or random effect had a significant influence on percentages of individual cell populations or ratios in blood or milk. A cutoff value of 0.495 for logarithmic polymorphonuclear neutrophilic leukocyte:lymphocyte ratio was established. Mean SCC of milk samples collected in the second trial was 543,230 cells/mL, and infection was detected in 53.1% of quarters, mostly caused by Staphylococcus aureus. When the cutoff value was applied to the data along with SCC, sensitivity and specificity of the diagnostic method were 97.3 and 92.3%, respectively.