FACTORS DETERMINING THE NUTRITIONAL-VALUE OF WHEAT-VARIETIES FOR POULTRY

The chemical composition of wheat is believed to influence its apparent metabolisable energy (AME) value for young poultry. In a preliminary study, 10 samples of wheat were assessed biochemically and AME was determined by chick bioassay. Diets were formulated to include wheat at 90%. Biochemical analyses of the wheat and excreta included starch, dietary fibre components, nitrogen, lipid and gross energy. Although the wheats tested did show a compositional variation, none were identified as being low-AME types. Mean values ranged from 11.98 to 14.90 MJ/kg of dry matter. Significant differences were found between the contents of starch (g/kg DM; range of 608-744, p < 0.001) and protein (N x 5.83, g/100 g DM, range of 9.57-14.69, p < 0.001), although these were not correlated with AME. AME was correlated with apparent starch digestibility in each trial (r2 = 0.96 and 0.74) and apparent starch digestibility was found to be independent of the NSP level or composition. The arabinoxylan content was not correlated with AME or energy metabolisability. No relationship was observed between the AME and starch or the non-starch polysaccharide (NSP) content. Recoveries of NSP from excreta were high (up to 86%) and AME was independent of NSP digestibility. A strong negative correlation (r2 = -0.92) existed between the AME and the ratio of arabinose-to-xylose in the NSP. Fractionation of the NSP into soluble and insoluble components revealed a variable ratio of between 0.28 and 1.00. No significant correlation existed between either of these two variables and the AME.