Correlation between bovine milk somatic cell count and polymorphonuclear leukocyte level for samples of bulk milk and milk from individual cows

The influence of various factors on the concentrations of polymorphonuclear neutrophilic leukocytes (PMN) in milk samples from bulk tanks and individu al cows was investigated. While somatic cell counts (SCC) and PMN level wer e in both cases significantly correlated, lower correlation coefficients we re found between SCC and PMN for samples of bulk tank milks than for milk s amples from individual cows. Furthermore, plots of PMN concentrations versu s SCC showed great variability in PMN in milk samples of similar total SCC. One factor that may lead to variability in bulk tank PMN levels was shown to be increased proportions of high SCC milk in the bulk tank mixture, whic h result in relatively high PMN levels without excessive elevation of total SCC. In milk samples from individual cows, it was found that there was als o a significant seasonal influence on milk PMN content, with milk from cows calving in the spring having, at SCC > 160,000 cells/ ml, higher proportio ns of PMN in the total milk SCC than milli from autumn calving cows. The re sults of this study suggest that the concentration of PMN may be a useful i ndicator of herd status in bulk tank monitoring schemes.