Lipid metabolism.

Traditionally, the study of lipid absorption and metabolism in farm animals has centred on the role of dietary lipids in provision of dietary energy and in processes of fat deposition in meat, milk and eggs. Interest in these areas remains intense because of the importance of fat deposition in determining the efficiency and, hence, profitability, of meat and milk production. The content and composition of fat in animal products has become increasingly important to consumer perceptions of the healthfulness of meat and milk. Although a normal part of animal growth or milk synthesis, fat synthesis decreases the efficiency of conversion of feed nutrients into lean meat or low-fat milk products that consumers desire. Furthermore, metabolism of lipids in the liver is an integral component of animal production and is a key factor in development of metabolic disorders such as ketosis and fatty liver. Consequently, this chapter will focus primarily on aspects of digestion, absorption and transport of dietary lipids, lipid synthesis, lipid mobilization and lipid metabolism in the liver. In addition to the primary and wellstudied roles of lipids as energy substrates, however, many new roles of lipids as biological mediators and second messengers in processes of signal transduction have been discovered in recent years. An overview of these functions will also be presented.