The composition of lipids in intestinal digesta of young pigs receiving diets containing tallow and tallow fatty acids

Three semipurified diets containing a low level of fat or 10% of either beef tallow or beef tallow free fatty acids were fed to young pigs. Jejunal digesta was sampled 1.5, 2.5, 3.5, and 4.5 h after feeding by aspiration through tubes leading from the jejunal lumen to the exterior. The samples were forced through Millipore filters (1 × 10−7 m pore size) to separate aqueous phase and oil phase lipid. The total and aqueous phase lipid was separated into triglyceride, monoglyceride, and free fatty acid, and the fatty acid composition of each fraction determined. The concentration of aqueous phase lipid was not influenced by diet, although the concentration of the oil phase lipid was generally higher for the addition of fat to the diets; the increase was greater for the beef tallow free fatty acid diet than for the beef tallow diet. Free fatty acids were the predominant component of the aqueous phase lipid along with some monoglyceride and traces of triglyceride. The major component of the oil phase lipid was free fatty acid but there were appreciable concentrations of triglyceride and monoglyceride. These must have been derived from endogenously secreted lipid in the case of the tallow fatty acid diet. Thus, the lower digestibility of completely hydrolyzed beef tallow than of conventional beef tallow was not due to an absence of monoglyceride in the intestinal lumen. The proportion of stearic acid in the jejunal digesta was greater than in the dietary lipid, whereas there were lower proportions of palmitic and oleic acids in the jejunal digesta than in the diet; the effect being most pronounced for the tallow free fatty acid diet. The ratio of oleic to palmitic acid in the aqueous phase was less than in the lipid phase suggesting preferential uptake of oleic acid from the micelle by the intestinal mucosa.