Lipolytic Enzyme Activity of Macrophages in Bovine Mammary Gland Secretions

The ability of macrophages isolated from the involuted bovine mammary gland and pooled raw milk to secrete lipolytic enzymes was investigated. Macrophages obtained from the involuted gland and maintained in cell culture secreted lipolytic enzymes into culture medium for up to 120 h. Leukocytes in pooled raw milk were separated using Ficoll discontinuous density gradients. Macro-phages secreted lipolytic enzymes into the gradient while fractions containing polymorphonuclear leukocytes and lymphocytes did not possess lipolytic activity. Enzyme activity of macrophages from pooled raw milk averaged .1% of the total milk lipoprotein lipase activity present in the original milk samples. Fresh raw milk with a macrophage concentration increased to 2.5 × 10⁶ cells/ml contained 11.6% higher milk lipoprotein lipase activity after storage for 48 h at 4°C. These results indicate that macrophages isolated from bovine mammary secretions produce lipolytic enzymes that could influence milk lipoprotein lipase activity in raw milk over storage.