Further studies on the changing composition of the digesta along the alimentary tract of the sheep

Boyne, Campbell, Davidson & Cuthbertson (1956) found in the digesta of the small intestine of the sheep a considerable increase in the concentration of nitrogen in the organic matter, and also relative to the insoluble ash over that found in its abomasum.It was later found to be greatest in the proximal quarter and diminish distally throughout the rest of the small intestine.It was independent of the time interval from the last meal, at least up to the 12 h interval between feeds.Work was then planned tostudy further these changes in nitrogen content of the digesta in the abomasum and the small intestine relative to lignin as well as to insoluble ash as reference markers.Lignin has a special position in relation to other reference markers, since it is a natural constituent of the ruminant's ration.The difficulty is that lignin is not well defined chemically, but in this laboratory it has been our experience (Walker & Hepburn, 1954-5) that it can be fairly accurately estimated by the 72% H,SO, (w/w) method modified by Ellis, Matrone & Maynard (1946).The originators of the method consider that, in the sheep, lignin is not digested, though variations of 6 yo digestibility were recorded.Gray (1947) is in general agreement with these findings.Forbes, Elliot, Swift, James & Smith (1946), using the same method, have also reported negligible digestibilities, but Thomas & Smith (1954-5) using a different but direct method found digestibilities of up to + 9.9 yo for the lignin of heather.In rumendigestion studies in cows, Hale, Duncan & Huffman (1947b) found mean digestion coefficients of 3.1 % for lignin, whereas the mean overall coefficient of digestion in the same animals was 21.5%.Though the validity of the determination of the coefficients of digestibility in the reticulo-rumen is still the subject of controversy, the available evidence suggests that such digestion of lignin as may take place is probably mainly in the large intestine.But direct proof is lacking.Additional evidence of occasional relatively high overall digestibilities is found in the work of Ely, Kane, Jacobson & Moore (1953) using the method of Ellis et al. (1946), who found overall digestion coefficients in cows of up to + 16.oyo.Balch (1957), using a method which he had previously found with his colleagues to give low to negative digestibilities, found in another experiment on cows total digestibility values ranging from -17.