Breakdown of plant carbohydrates in the digestive tract of pigs fed on wheat- or oat-based rolls

Cell wall materials from various cellular tissues of cereals may potentially influence the digestion and absorption processes in different ways. The objective of the present investigation was to study the breakdown of plant carbohydrates in the gastrointestinal tract of pigs fed a low-fibre (LF; 65 g kg−1 dry matter) wheat flour-based diet and two high-fibre diets with added insoluble fibre from wheat bran (HFWB; 112 g kg−1 dry matter) or soluble fibre from oat bran (HFOB; 108 g kg−1 dry matter). The diets were formulated to provide ∼0.31 energy from fat, ∼0.18 energy from protein and ∼0.51 energy from carbohydrates and were offered as baked rolls to eight ileum-cannulated hypercholesterolemic pigs in a crossover design. Carbohydrates were the predominant ileal constituent, with most of the carbohydrates present as non-starch polysaccharides (NSP). Starch in all diets was almost completely digested at this site of the gastrointestinal tract, with digestibility values above 0.99. The ingested amount of NSP was quantitatively recovered in ileal materials with the wheat-based diets, while there was a significant loss of 0.27 of NSP primarily as mixed linked (1→3)(1→4)--D-glucan with diet HFOB. The concentration and flow of lactic acid were also highest in the ileum after feeding diet HFOB, indicating that -glucan stimulated lactic acid formation. Any soluble components that reached the large intestine were almost completely broken down, while the digestibility of insoluble NSP constituents was significantly lower for diets LF and HFWB than for diet HFOB. The high degradation of oat bran resulted in a lower effect on faecal dry and wet bulking than was found with wheat bran. In conclusion, cereal starch was practically completely degraded in the small intestine, while the site and extent of NSP degradation, lactic acid formation and bulking properties were influenced by the fibre source.