Influence of mastitis on cheese manufacture

When a cow has mastitis, the concentration of white blood cells (commonly called somatic cells) increases in milk. Somatic cells that are present in milk during an infection are involved in the conversion of plasminogen to plasmin. Plasmin is a proteolytic enzyme produced by the cow that can break down casein and decrease cheese yield. Decreased cheese yield, when milk SCC is high, is caused by increased loss of casein and fat into whey during cheese making. Variation in milk SCC only explains about half of the variation in milk plasmin activity and casein damage. Other causes of variation in plasmin activity and casein damage are stage of lactation, health history of the animal, and number of lactations. These factors may interact with a high current milk SSC to produce larger-than-expected decreases in casein as a percentage of true protein and cheese yield efficiency.