Enzyme supplementation of dry and wet wheat-based feeds for broiler chickens: performance and gut responses

To test whether the improvements in digestive efficiency due to either wetting of the food or inclusion of enzymes are accompanied by the same changes in gut function, foods with a high content of wheat were fed to broiler chicks from 1-42 d old. Twenty-four birds were caged individually while a further sixty-four were in group pens in experiments of 2 x 2 factorial design with two levels of enzyme (0 or 1 g/kg, designed for wheat) and two levels of water addition (0 and 1300 g/kg). Food intake and live-weight gain were significantly increased by wet feeding (from 89.3 to 153.4 g/d and from 39.7 to 65.4 g/d respectively), the differences increasing with age, while the enzyme had no significant effect (120.5 and 122.2 g/d and 51.9 and 53.1g/week respectively). The viscosity of digesta was greatly reduced both by wetting (from 4.40 to 2.64 kPa. s) and enzyme (from 4.47 to 2.57 kPa. s) but there was a significant interaction with age in which the viscosity was low throughout in the wet only, enzyme only and wet + enzyme treatments but declined with age from a very high level in the dry, no enzyme treatment (11.5 kPa. s at 14 d). While wetting increased weight and length of digestive tract and thickness of some parts of the gut, enzyme had no significant effect, tending to reduce gut wall thickness. Crypt cell proliferation rate (CCPR) was significantly reduced by wet feeding (from 39.4 to 28.7 cells/crypt per 2 h) and by enzyme supplementation (from 38.9 to 29.2 cells/crypt per 2 h). Therefore, while both wetting and enzyme addition to the food reduced digesta viscosity and CCPR to a similar extent, the former had marked stimulatory effects on food intake and weight gain while the latter had little effect. The mode of action of wet feeding is therefore deduced to be not primarily through its effects on viscosity and CCPR.