Total and differential bulk cow milk somatic cell counts and their relation with lipolysis

In the present study, the relationship between total bulk milk somatic cell counts (BMSCC), differential BMSCC (macrophage, lymphocyte and polymorphonuclear leukocytes) and lipolysis level was investigated. Eighty samples of bulk milk were selected randomly from eight dairy farms in the region of Sfax (Tunisia) from November 2005 to April 2006. Bulk milk samples were analyzed for titratable acidity, total solids, fat content, lipolysis level, total and differential SCC. After that, milk was allotted according to their total SCC to; group 1: bulk milk with SCC below 1000 × 103/ml, group 2: bulk milk with SCC that ranged from 1000 × 103 to 1500 × 103/ml and group 3: bulk milk with SCC above 1500 × 103/ml. BMSCC levels ranged from 400 × 103 to near 4000 × 103/ml. Lymphocytes were the predominant cell type in all groups, but their proportion declined with total BMSCC. In this study, polymorphonuclear leukocytes (PMN) and lymphocyte (LYM) were significantly (P < 0.001) correlated with total BMSCC. BMSCC did not affect acidity and total solids, but at high level, increase the fat content. A significant (P < 0.001) positive relationship was observed between total BMSCC, the PMN population and lipolysis level in milk. It has been suggested that milk cells, especially PMN, could be responsible for sufficient lipolysis of milk fat.