Lactose in diet influences the degradation of mixed linked β(1-3;1-4)-D-glucan in the small intestine of pigs.

The objective was to study the cause of variation in digestibility of mixed linked β(1-3;1-4)-D-glucan (β-glucan) in the small intestine of growing pigs. The β-glucan is an important cell wall [dietary fiber (DF)] component of the endosperm of barley (Hordeum vulgare) and oats (Avena sativa). The digestibility of β-glucan in the small intestine from both cereals is among the highest of all DF components, but in 1 study with oat-based diets it was lower (P < 0.001) than in other studies. In this study, whey protein containing lactose was used as protein supplement. Lactose is slowly digestible in the small intestine. To investigate if lactose might cause the lower digestibility of β-glucan in the study with whey protein, the lactose in diets was analyzed together with lactose and organic acids (lactic acids and short-chain fatty acids) in digesta samples from the small intestine (the small intestine was by length divided in 3 equal segments: SI(1), SI(2), and SI(3)) and ileal digesta. Diets containing lactose were based on oat goats, oat flour, and oat bran (12 to 38 g lactose/kg DM) whereas the reference diets were based on rolled oats, rolled oats and oat bran, wheat (Triticum aestivum) flour with added oat bran, and wheat flour with added β-glucan (0 to 1 g lactose/kg DM). Lactose was identified in digesta up to SI(2) but disappeared in digesta from SI(3) and ileum. Digestibility of β-glucan did not differ among diets up to SI(3) (18% average) whereas digestibility in ileum was 64% in diets without lactose and 27% in diets containing lactose (P < 0.001). The β-glucan was virtually completely digested in the cecum (96% average) in all diets. The concentration of organic acids did not differ between diets either in SI(3), ileum, or cecum. In conclusion, slowly digestible lactose was the most likely cause of the reduced digestibility of β-glucan in oat diets containing lactose.