Optimized flow cytometry for differential somatic cell count in goat milk: Implications for milk quality and udder health

• Flow cytometry method was optimized to assess differential somatic cells in goat milk. • Differential somatic cell count allows rapid, accurate assessment of goat udder health. • Assessing milk based on PMN values improves insight into goat milk quality and use. This study presents the optimization of a flow cytometry protocol for the differential somatic cell count in goat milk. The methodological refinement focused on the effective sample preparation, including cell isolation, followed by fluorescent labeling using a targeted panel of fluorochrome-conjugated antibodies to enable the identification of major somatic cell subpopulations—namely, epithelial cells, polymorphonuclear neutrophils (PMN), macrophages, and lymphocytes by flow cytometric analysis. The optimized method was applied to 39 individual goat milk samples. The results demonstrated that differences in cellular immune activity were detectable even among samples with low microbiological findings. Milk samples with minor but detectable microbial findings exhibited a significantly higher proportion of leukocytes compared to samples without microbial detection, with mean leukocyte proportions of 66.6 % vs. 46.9 %, respectively (P = 0.038). A further analysis revealed that a high PMN proportion (>77 %) was significantly associated with decreased casein content (P = 0.024), reduced total protein (P = 0.030), a shorter rennet clotting time (P = 0.056), and a slight increase in lactose concentration (P = 0.035). These findings suggest a negative impact of elevated PMN levels on the technological quality of goat milk. Optimized flow cytometry is a useful tool for goat milk quality management.