Relationship between somatic cell count, individual leukocyte populations and milk components in bovine udder quarter milk

The somatic cell count (SCC) in bovine milk is an indicator of udder health and milk quality. Individual cell populations, i.e., macrophages, lymphocytes and polymorphonuclear neutrophils, were identified and their relationship to milk components such as acute-phase proteins (serum amyloid A (SAA) and α1-acid glycoprotein), lactic acid and lactoferrin (LF), as well as protein, fat and lactose, were studied in foremilk from separate udder quarters. The whey proteins and peptides were studied using two-dimensional gel electrophoresis, which was shown in the present study to be a useful method of assessing udder health and milk quality. The growth of a starter culture was evaluated using a conductance method as a simulation of fermentation processes relevant for cheese production. The investigation showed that LF, SAA, l-lactate and lactose are reliable indicators of milk quality on udder quarter level. The correlations between SCC, or the individual cell populations, and the potential indicators were highly significant.