DISTRIBUTION OF LEUCOCYTES AND EPITHELIAL CELLS IN SHEEP MILK IN RELATION TO THE SOMATIC CELL COUNT AND BACTERIAL OCCURRENCE: A PRELIMINARY STUDY
Keywords:
sheep, milk, SCC, bacteria, leukocytes, flow cytometryAbstract
Milk somatic cell count (SCC) is a main indicator of udder health in dairy animals. Thus, increased SCC levels are usually associated with the clinical and/or subclinical intramammary infections. SCC are mainly composed of immune cells (leukocytes) and epithelial cells. Recently, several flow cytometric approaches were used to assess the distribution of these cells in the milk of ewes. Hereby, a new combined antibody panel was designed for this purpose. Briefly, milk cells were stained with specific antibodies: CD18 (leukocytes), CD21 (B cells), CD4 (Th cells), CD8 (Tc cells), CD14 (monocytes) and CD11b (polymorphonuclear cells – PMNs). CD18 negative cells were considered as epithelial cells. Moreover, a qualitative examination of bacteria species presented in the milk was carried out using MALDI-TOF MS. Analysed milk samples were divided into 5 classes according to the SCC number as follows: < 300,000 cells.ml-1 (SCC1), 300,000-500,000 cells.ml-1 (SCC2), 501,000-1,000,000 cells.ml-1 (SCC3), 1,001,000-2,000,000 cells.ml-1 (SCC4) and > 2,000,000 cells.ml-1 (SCC5). SCC1-2 samples were considered as normal milk samples, whereas SCC3-5 as abnormal samples. Bacteriological assessment revealed that all samples in SCC3-5 class were infected mainly by S. epidermidis and S. caprae. On the other hand, SCC2 did not exhibit a pathogen infection and in SCC1 only 22 % of samples were infected. Concerning the somatic cell composition, SCC1-2 classes comprised approximately 50:50 of leukocytes and epithelial cells. The main leukocyte subsets were PMNs. However, the number of leukocytes alongside with PMNs count significantly (P < 0.05) increased in SCC3, whereas the number of epithelial cells significantly (P < 0.05) decreased compared to SCC1-2. Similar trend, although not significant, was observed in SCC4-5 samples. The proportion of nonviable PMNs also increased (P < 0.05) in SCC3, however it was not markedly different in comparison to live PMNs among all SCC classes. In conclusion, described methodological approach could be effective in the more detail further research dealing with distribution of different cells of different origin (epithelial, leukocytes) in cases of subclinical mastitis caused by different mastitis pathogens.
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