Starch Digestion in Fowl

Starch is usually the largest single nutrient in feed and provides the greatest proportion of metabolizable energy. Amylose and amylopectin comprise starch and are packed by plants in granular form. Granule stability is a function of the proportions of each polymer and the manner in which they are crystallized. Plant source determines granule size and stability. Grains generally have granules that are smaller and less stable than tuber or legume sources. Pancreatic alpha-amylase is the only enzyme elaborated by fowl that digests starch. Avian and mammalian sources are very similar, and inhibitors would not ordinarily be encountered in practice. The primary products of amylose digestion are maltose and maltotriose which further include alpha-limit dextrins when amylopectin is the substrate. Having starch in granule form reduces polymer access by the enzyme, and digestion difficulties occur in proportion to stability of structure. Moisture combined with heat destabilize granule structure and their use at one time or another in the manufacture of most feeds alleviates digestibility problems. Large amounts of the enzyme are present with the chick at hatch, and the pancreas is more than capable of synthesis commensurate with need. Gelatinization, enzyme adequacy, predominance of starch from grain, and lack of inhibitors account for the relative absence of practical problems involving this nutrient.