Variation in milk fat content and fatty acid composition of Jersey and Friesian cattle

The milk fat content and fatty acid composition were determined from Jersey and Friesian cows ranging from mid to late lactation. Jersey milk (5.7iO.3%) contained significantly more fat than Friesian milk (4.5*0.3%) and Friesian milk was less saturated. Generally, the higher the milk fat content, the more saturated the fat. The activity of the A9-desaturase enzyme was not influenced by fat content so at any given fat content, Friesian milk was less saturated than Jersey. Hence the association of low unsaturated fat and high fat content was most likely due to low availability of the precursor of unsaturated fat; C18:O. Thus, in mid-late lactation cows alter rates of de nova synthesis of fat in the mammary gland rather than increasing the incorporation of fat from blood into milk.