Factors influencing somatic cell count and leukocyte composition in cow milk: A field study.

In recent years, a proliferation of studies investigating the composition of milk SCC, focusing on neutrophils (NEU), lymphocytes (LYM), and macrophages (MAC) has occurred. These 3 components are indeed crucial for the animal's immune response to mastitis-causing pathogens. The study examined various factors influencing SCC and leukocyte components in cow milk, including lactation stage, parity, and milk electrical conductivity, using data from 179 dairy cows across 6 farms throughout the entire lactation. Statistical analyses, including mixed models and logistic regression, were employed to investigate the relationships between these variables and identify risk factors for high SCC levels. Results showed that factors such as parity and lactation stage were significantly associated with somatic cell composition. In particular, the highest milk NEU values (>60% of the total leucocytic fraction) and lowest MAC values (<20%) were found at the beginning and end of lactation, which are the critical periods for udder health. High milk electrical conductivity, low milk production, parity number, and poor hygiene scores were identified as contributing to increased SCC. Additionally, elevated percentages of NEU and LYM in milk were associated with increased risk of high SCC values, indicating potential udder health issues.