Intestinal absorption of fatty acids, and blood lipid composition in sheep.

Interrelationships between intestinal uptake of fatty acids and their concentrations in lipids of blood plasma of sheep were assessed by quantities of individual fatty acids that flowed through and were absorbed from the intestinal tract under different dietary conditions. Major long-chain fatty acids were approximately 90% digested, thus demonstrating that dietary fatty acids of high melting points can be absorbed efficiently by ruminants provided they are well dispersed. Relationships were linear between uptakes of 16:0, 18:0, 18:1, and 18:2 fatty acids from the gut and their concentrations in both triglycerides and triglyceride-free plasma lipids. The proportion of each transferred to triglyceride-free plasma lipids was in order 18: 2 greater than 18:1 greater than 16:0 greater than 18:0, whereas in plasma triglycerides the order was 16:0 = 18:0 = 18:2 less than 18:1. Interconversion of 18:0 to 18:1 by intestinal mucosa may explain the anomalous behavior of 18:1 triglycerides. These results are consistent with the hypothesis that the intrinsic nature of the fatty acid primarily determines the composition of triglyceride-free plasma lipids whereas the relative amount of each acid absorbed by the intestine determines that of plasma triglycerides and, hence, of milk and depot fats of ruminants.