Dietary free fatty acids complex with amylose creating another form of resistant starch: Gastrointestinal formation with fowl and swine

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 toα-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 poorquality 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.Althoughα-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.

Large intestinal dynamics differ between fowl and swine:Anatomical modifications,microbial collaboration,and digestive advantages from fibrolytic enzymes

The large intestinal systems of fowl and swine recover nutrients from ileal indigesta by a strategically different manner.Indigesta with fowl enter a short colon where retro-peristalsis using urine from the urodeum carries small particulates and solutes into both ceca while coarse materials collect in the cloaca.Fowl repetitively add fine and soluble materials into both ceca to continue fermentation until complexity of the remainder exceeds microbial action,then contents apart from faeces are entirely evacuated.Indigesta with swine initially enter a short cecum followed by a lengthy progression through to the rectal ampulla.Wall out-pocketings of circular muscle or haustrae occur throughout the length of the pig's cecum and helicoidal colon.Each pocket carries contents acquired earlier in the cecum.Motility collects fines and solutes into haustrae during their progression through the colon whereas coarse particulates assemble in the core.Haustrae contents continually ferment during movement to the distal colon with resulting volatile fatty acids(VFA)and electrolytes being absorbed.Mucin loosely covers the lumen surface in caeca as well as helicoidal colon that may capture microbes from active intestinal contents as well as release others to sustain fermentation.The microbial community continually modifies to accommodate fibre complexity as encountered.Resistant starches(RS)and simple oligosaccharides rapidly ferment to yield VFA while encouraging butyric acid in the cecum and anterior colon,whereas non-starch polysaccharides(NSP)complexity requires extended durations through the remaining colon that enhance acetic acid.Residual fibre eventually results in undue complexity for fermentation and consolidates at termination of the colon.These compact pellets are placed on core contents to form faeces having a nodular surface.Acetic,propionic,and butyric acids represent the bulk of VFA and are derived from non-digestible carbohydrates.Fibrolytic enzymes,when supplemented to feed,may increase the proportion of oligosaccharides and simpler NSP to further the rate as well as extent of fermentation.Active absorption of VFA by mucosal enterocytes employs its ionized form together with Na^(+),whereas direct membrane passage occurs when non-dissociated.Most absorbed VFA favour use by the host with a portion of butyric acid together with by-products from protein digestion being retained to reform mucin and sustain mucosal integrity.