Concepts in Lipid Digestion and Metabolism in Dairy Cows

Fat and fatty acid metabolism and digestion in the dairy cow are of considerable interest, both to scientists and the dairy industry. This renewed interest is based on several reasons; first, the use of dietary fat supplements has increased, and will continue to do so, as nutritionists strive to increase the energy density of diets to meet requirements of the high producing dairy cow; second, we now recognize that fatty acids, both of dietary and rumen origin, can have specific and potent effects on ruminant metabolism and human health; and third, we now recognize that specific fatty acids produced in the rumen are potent regulators of milk fat synthesis in the mammary gland. Our objective in this review is to provide an overview of lipid metabolism in the dairy cow. Our focus will include the biological processes and quantitative changes occurring during the metabolism of fatty acids in the rumen and their subsequent absorption in the small intestine. In addition, we will discuss the interrelationship between rumen lipid metabolism and milk fat synthesis, and dietary factors that result in milk fat depression.