Abstract
Fat added to poultry and swine feeds often contains abundant free fatty acids (FFA) that can impair digestible energy (DE). Placement of the fatty acid (FA) hydrocarbon chain in the helix core reformed from amylose creates a complex of both nutrients. Resulting modifications create a new structure termed the V-helix that becomes resistant to α-amylase. Granules in grain naturally contain minimal amounts of these complexes with more being generated during food manufacturing when moisture and heat release amylose in the presence of FFA. A paucity of FFA usually exists in complete feeds without sources of poor-quality fat. Animal fats and by-product meals from rendering are prominent in their saturated FFA content which favorably complex within the helix. V-helix-FA complexes may arise during their concurrent encounter of FFA together with amylose during feed manufacture, particularly pelleting. FFA in the gastrointestinal tract (GIT) are speculated to further form complexes when present together with amylose. Although amylose may be dissolved in the gastric and small intestinal milieu, FFA separately coalesce into hydrophobic fat droplets along with other dietary lipids. Formation of complexes is likely restricted until FFA are released into the aqueous phase during fat digestion. Although α-amylase may be prominent, V-helix-FA complexes being resistant to enzymic attack pass into the large intestine. Subsequent microbial catabolism of V-helices may generate volatile fatty acids that are absorbed by the mucosa; however, an inability to use FFA once released leads to their excretion and basis for decreased DE. Immature microbial populations with young animals usually lack the capacity to fully catabolize the V-helix, further extending the loss in DE.