Origin and Formation of Lymph Lipids in the Sheep

3H and 14C‐labelled palmitic, stearic, oleic, linoleic and linolenic acids introduced into the duodenum of sheep were recovered in thoracic duct lymph, and the specific radioactivities of the fatty acids in the various lipid fractions were determined. Lymph fatty acids were transported mainly as triglycerides (77%) and phospholipids (18%), probably mostly in the form of very low density lipoproteins rather than as chylomicrons. Lymph triglycerides transported most of the palmitic, stearic and oleic acids (74–79%) whereas phospholipids were important in the transport of the essential fatty acids, linoleic and linolenic acids (54% and 38% respectively). Specific radioactivity measurements indicated that part of the lymph cholesteryl ester and phospholipid fatty acids were of a non‐radioactive origin. In lymph phospholipids 52% of the linoleic acid, 81% of the linolenic acid and more than 88% of the palmitic, stearic and oleic acids were derived from endogenous esterified sources. Evidence is presented to indicate that the major part of lymph phospholipids could be derived from biliary phospholipid. The possible roles of bile and pancreatic juice in fat absorption in the ruminant are discussed.