Factors Affecting the Patterns of Total Amount and Proportions of Leukocytes in Bovine Milk

摘要

Differential leukocyte count (DSCC) in milk is considered important to improve our knowledge on udder immune response since it describes the proportions of leukocytes in milk. However, we hypothesized that the total amount of each cell population in daily milk production would be even more useful. Therefore, we analyzed the pattern of both DSCC and the total amount of polymorphonuclear neutrophils (PMN) + lymphocytes (LYM) (P + LT), calculated as SCC × milk yield × DSCC (as proportion). Cows with ≤200,000 cells/mL have a P + LT average between 5.0 × 10 and 3.0 × 10 cells. In cows with SCC >200,000 cells/mL, the values were 1.6 × 10 and 2.5 × 10 cells. Therefore, the presence of a well-defined inflammatory process increased the overall amount of PMN and lymphocytes LYM of 1 log, from 1 × 10 to 1 × 10 . The assessment of the total amount of PMN and LYM, to our knowledge, has never been reported in scientific literature and the value reported may be proposed as benchmarks for studies on udder immune response. The results of this study showed that cows in first and second lactation have a significant lower amount of PMN + LYM, when compared to cows in third and higher lactation. However, these differences are numerically not very large (7%), suggesting that, in healthy animals, the number of immune cells is kept as constant as possible. To the best of our knowledge, this is the first study describing the pattern of DSCC and the total amount of PMN + LYM in relation to parity, days in milk, and SCC, and it may be considered as a first contribution in the investigation on mammary gland immune response by means of differential cell counts in milk.