Comparison of fat and cream content in normal and mastitic milk of cows

Two methods for estimating fat and cream content in cow's milk were compared in normal and mastitic milk. Fat content in milk from periparturient cows was estimated simultaneously by the method of Gerber and by simply spinning small samples of untreated milk in a haematocrit centrifuge. Mastitis was experimentally induced by inoculating mammary glands with Escherichia coli. On the average, cream content in milk from normal, and uninfected mammary glands measured by the haematocrit method was 20 to 23% higher than milk fat measured by the method of Gerber. In mastitic milk from infected mammary glands haematocrit readings were 40% higher than those of Gerber. Milk fat values as measured by both methods were highly correlated. It is concluded that the haematocrit method can be used for rapid estimation of milk fat content in normal milk of cows. The greater difference between cream and fat content in mastitic milk compared to normal milk can probably, at least partly, be ascribed to the presence of large clots of cells and fat in the milk during mastitis. During centrifugation of the viscous mastitic milk samples, milk cells and fat probably are not completely separated. This results in overestimated readings of milk cream content with the haematocrit method. It therefore seems advisable to use the Gerber method for accurate measurements of milk fat in mastitic milk.