DIGESTION OF POLYSACCHARIDES AND OTHER MAJOR COMPONENTS IN THE SMALL AND LARGE-INTESTINE OF PIGS FED ON DIETS CONSISTING OF OAT FRACTIONS RICH IN BETA-D-GLUCAN

The digestibility of polysaccharides and other major components and th e metabolic response of the microflora in the small and large intestin es to oat diets varying in mixed linked B(1-->3; 1-->4)-D-glucan (beta -glucan) were studied in experiments with ileum-cannulated pigs. The o at fractions for diets were prepared in a dry milling process in which oat groats were milled into two endosperm fractions (oat flour 1 and oat flour 2) and oat bran. The digestibility of polysaccharides and th e metabolic response of the microflora were followed for the two contr asting diets, oat flour 1 and oat bran, from ingestion to excretion wh ile the digestibility of oat groats and oat flour 2 were estimated onl y at the ileum and in faeces. There was no degradation of beta-glucan from either oat flour 1 or bran in the stomach and the first, middle a nd distal thirds of the small intestine (average digestibility approxi mately 0), while in the terminal ileum digestibility increased to 0.30 to 0.17 respectively. The digestion of starch in the first third of t he small intestine was lower for the high-beta-glucan oat-bran diet (0 .49) than for the low-beta-glucan flour diet (0.64). However, digestib ility differences between the two diets levelled out as the digesta mo ved aborally in the small intestine and the digestibility at the termi nal ileum nas almost complete (0.970-0.995) for all diets. Oat non-sta rch polysaccharides (NSP) were an easily digestible energy source for the microflora in the large intestine less than 13% of dietary NSP bei ng recovered in faeces. The bulk of beta-glucan which survived the sma ll intestine was degraded in the caecum and proximal colon while arabi noxylan was more slowly degraded. The amount of residues passing the i leo-caecal junction has little impact on the density of micro-organism s in the large intestine, which on the flour and bran diets were in th e range of 10(10)-10(11) viable counts/g digesta, but a high impact on the activity of the flora in colon. Oat bran resulted in a higher pro portion of butyric acid in large intestinal content compared with the flour diet. The faecal bulking effect of oat bran was mainly caused by an increased excretion of protein and fat, presumably of bacterial or igin. Of all the diets tested the oat-bran diets had the lowest digest ibilities of protein and fat at the terminal ileum and in the faeces.