LIPID ABSORPTION AND TRANSPORT IN RUMINANTS

The objective of this paper is to review new insights on the biologica l mechanisms of absorption and transport of lipid in ruminants, especi ally the modern concepts and analytical methods used in studies on str uctural properties and intravascular and tissue metabolism of lipoprot eins and their factors of variation. The intestinal absorption of lipi ds (including long-chain fatty acids) is detailed, and variations in t he qualitative and the quantitative aspects of absorption with diet co mposition, especially for high fat diets, are presented. Also, structu ral properties and distribution characteristics of lipoprotein classes in different lymphatic and blood vessels are compared across several animal species. Physicochemical and hydrodynamic properties of the lip oprotein particles and their apolipoprotein moieties are given for the main classes of lipoproteins. Finally, lipoprotein metabolism is disc ussed in relation to development and physiological, nutritional, and h ormonal status. Intravascular metabolism of lipoproteins, including th e role of lipolytic enzymes and lipid transfer proteins, is presented. Characteristics of the intestinal and hepatic synthesis of lipoprotei ns and apolipoprotein fractions are compared, especially through exper iments stimulating the hepatic secretion of triglyceride-rich lipoprot eins. Different methods of measurement of lipoprotein tissue uptake or secretion in ruminants are discussed.