The absorption of long-chain fatty acids from the small intestine of the sheep.

I . Three sheep, each of which was fitted with a rumen cannula and with two pairs of reentrant cannulas in different parts of the small intestine, were used in this study. They were fed on dried grass cubes or hay plus linseed meal and oats: an aqueous solution of polyethylene glycol (PEG) was infused continuously into the rumen. 2. Total lipids were extracted from samples of the chyme entering and leaving the different lengths of the small intestine embraced by the respective cannulas. The lipids were fractionated into unesterified fatty acids, neutral lipids and phospholipids and the contribution of each fraction to the total fatty acids was determined. The samples were also analysed for their PEG content, thus affording an index of the extent to which water had been absorbed from each particular length of intestine. 3. From the above tindings and a knowledge of the flow-rate of the digesta, the uptake of unesterified fatty acids and the degree of dissimilation or uptake, or of both, of esterified fatty acids was calculated. 4. The results indicated that, by the time the digesta reached the ileum (Le. the distal half of the small intestine), the uptake of fatty acids was almost complete, as was aIso the hydrolytic release of esterified fatty acids. 5 . Though there were no gross differences in the overall composition of the unesterified and esterified fatty acids in different parts of the small intestine, it appeared that C,, mono-unsaturated acid, the principal unsaturated unesterified acid, was absorbed somewhat more efficiently than were the major saturated acids (palmitic acid and stearic acid).