Abstract: Fat content and composition of milk can be markedly affected by diet. Conjugated linoleic acids(CLA) are functional food components of milk fat that may have positive effects on human health and disease prevention. CLA is formed in the rumen by anaerobic bacteria as an intermediate in the biolydrogenation of linoleic acid, while the major source of milk CLA was of endogenous origin through Δ9 desaturase from trans11 C18∶1 in the mammary gland. A number of studies have shown that the differences among diets, individual animals and Δ9 desaturase in mammary gland are the key factors which affecting milk CLA synthesis. The following part will give a brief viewpoint related to Factors affecting trans 11 vaccenic acid and CLA synthesis of milk fat.

Key words: conjugated linoleic acid; milk fat; trans 11 vaccenic acid; dairy cattle