Differentiation of leukocytes in bovine milk

The somatic cell count (SCC) in milk is used as an indicator of udder health status. Elevated SCC are generally considered as an indication of mastitis. In addition, the differential cell count of milk somatic cells can be a useful tool in research because each cell type has its own specific function in the immune response. The aim of this study was to develop and validate a staining method for milk somatic cells. Therefore the panoptic staining method according to Pappenheim was adapted for the differentiation of milk somatic cell populations. Quarter composite milk samples from 28 German Braunvieh x Brown Swiss cows were separated into 3 groups based on their SCC levels. Group 1 consisted of 12 samples with a mean of 4.57 ± 0.10, group 2 of 8 samples at a mean of 5.39 ± 0.06 and group 3 of 8 samples at a mean of 6.15 ± 0.07 log₁₀ cells/ml, respectively. Results showed a distribution of lymphocytes, macrophages and neutrophils of 20.9, 45.6 and 33.5% in group 1, of 11.4, 25.1 and 63.5% in group 2 and of 3.3, 9.5 and 87.2% in group 3, respectively. In conclusion, the ratio of lymphocytes and macrophages decreases whereas the ratio of neutrophils increases with rising SCC.