Interactions between dietary fat type and xylanase supplementation when rye-based diets are fed to broiler chickens....

1. The interactions between fat type and xylanase supplementation of rye-based diets were investigated using a 2 x 2 factorial design in which a rye-based diet (610 g rye/kg) was combined with 100 g/kg of soya oil or beef tallow, with and without xylanase supplementation at 3000 IU/kg, and fed to 1-d-old male broilers. Food passage time, viscosity of digesta supernatant, xylanase activity and pH in different segments of the digestive tract were examined. 2. Food passage throughout the digestive tract was accelerated by enzyme addition regardless of fat type. The time taken for 50% of the marker to be excreted was reduced from 8.4 to 6.7 h in animals receiving the rye-soya oil diets and from 8.0 to 6.9 h with the rye-tallow diets. 3. Viscosity in the supernatant of the jejunal and ileal digesta was markedly decreased after enzyme addition. Viscosities were generally higher in the ileal than in the jejunal supernatant, and fell as the birds aged from 14 to 28 d. The effect of enzyme was also reduced in older chicks. There was not a clear effect of the fat source on viscosity. 4. Xylanase activity was still found at the end of the ileum in digesta of birds fed on the enzyme-supplemented diets but not in control animals. Xylanase activity was also detected in the caeca of all groups. 5. Significantly lower pH values were found in tallow-fed birds in some segments of the digestive tract. A significant increase in pH after enzyme addition was detected in the proximal ileum; this was independent of fat source.