Use of inflammatory cell activities in bovine milk to diagnose mastitis

The activity of leukocytes, determined by chemiluminescence (CL) emission, was compared with the somatic cell count (SCC) in 4,883 quarter-milk samples from 132 dairy cows. The presence of bacteria was determined by bacteriologic culture of samples in which SCC and CL were high. Chemiluminescence was measured with an automated illuminometer system at 37 C after separating the leukocytes from milk by allowing them to adhere to cotton-wool swabs. Chemiluminescence emission was induced by opsonized zymosan and enhanced by luminol. After luminol and zymosan were added to the measuring vials containing the swabs, CL emission increased rapidly, reaching its maximum usually at about 15 minutes of reaction time, and decreasing slowly thereafter. In general, good correlation was found between CL and SCC (r = 0.876; P less than or equal to 0.001; n = 4,883). Even milk samples with low SCC gave reliably measurable CL signals. Minor pathogens in the milk caused about a sevenfold increase in both SCC and CL, whereas major pathogens caused 14- and 25-fold increases in SCC and CL, respectively. The diagnostic situation that requires both sensitivity and specificity to be at least 90% was attained only by the CL assay for major pathogens. These results suggest that the measurement of milk leukocyte activity by CL assay applies well to the diagnosis of mastitis, and has the potential to become a large-scale laboratory test, as well as a simple cowside test.