Differential cell count of caprine milk by flow cytometry and microscopy

There is currently no consensus about the usefulness of somatic cell counts (SCC) as a key diagnostic criterion for the evaluation of caprine udder health. While traditional differential cell count by microscopic analysis may provide a more reliable basis for the detection of mastitis, this procedure is labor intensive and time consuming, due to the presence of cytoplasmic particles (CP), and thus cannot be considered for routine use. Although flow cytometric methods have been described for quick cell differentiation in cow’s milk, there has been little investigation of such methods for goat somatic milk cells. The present study was therefore intended to develop a simple and quick method for differentiating caprine somatic cells by flow cytometry and to compare these results with microscopic analysis using two different staining methods. Milk samples were obtained from 25 German Brown goats and analyzed microbiologically for potentially udder-pathogenic bacteria and for SCC. In a preliminary study, somatic milk cells were incubated with specific monoclonal antibodies binding to different cell populations and simultaneously stained with the fluorescent dye SYTO® 13. In the main experiment, it was then possible to localize the exact positions of viable and non-viable polymorphonuclear neutrophils, lymphocytes, and macrophages within SYTO® 13 flow cytometric dot plots. The percentages of the cell populations were determined by a simple and quick incubation of cells with SYTO® 13 and DRAQ5TM followed by flow cytometric measurement. This method allows to determine differential cell counts in goat milk rapidly and objectively.