CHANGES IN THE COMPOSITION OF MILK FROM HEALTHY AND MASTITIC DAIRY-COWS DURING THE LACTATION CYCLE

Variations in milk composition during lactation were studied in normal and mastitic dairy cows from 2 seasonally calving herds in northern Victoria. Milk yields, somatic cell counts (SCC), and concentrations of lactose, fat, total protein (TP), casein protein (CP), non-casein protein (NCP), sodium, potassium, and calcium varied considerably as lactation progressed. The basic patterns of change over lactation were similar whether cows were healthy or mastitic (SCC > 3 x 10(5) cells/mL milk). Milk from mastitic cows had higher concentrations of TP, NCP, and sodium, but lower concentrations of fat, lactose, CP, and potassium, than milk from healthy cows, although differences were not consistently significant. The activity of the milk protease, plasmin, was positively correlated with log(10)SCC in both herds.