Anti-nutritive effect of wheat pentosans in broiler chickens: roles of viscosity and gut microflora.

1. The mechanism of the anti-nutritive activity of isolated wheat pentosans was investigated by examining the roles of digesta viscosity and gut microflora in broiler chickens. 2. Wheat pentosans were isolated by alkaline extraction and purified by sequential treatment with pancreatin, alpha-amylase and lichenase, and high-speed centrifugation. Some of the pentosans were depolymerised using a beta-xylanase, which reduced the relative viscosity of the polysaccharides 4 fold. 3. Inclusion of 35 g alkali-extractable pentosans (containing 854 g arabinoxylans/kg DM) per kg diet significantly (P less than 0.05) depressed broiler performance and the viscosity of the digesta of these birds was significantly (P less than 0.05) higher than that of controls. Addition of the same amount of depolymerised pentosans had no significant effect on bird performance and had less effect on digesta viscosity. 4. Supplementation of the diet containing wheat pentosans (30 g/kg) with procaine penicillin (150 mg/kg) did not improve bird performance. 4. It is concluded that the wheat pentosans elicit their anti-nutritive activity predominantly through increasing the viscosity of digesta.