8/26/20131Digestive Systems and DigestionANSC/NUTR 303Why do animals digest feed?• Food not ingested in a suitable state• Physical nature of feed determines– Gathering apparatus for upt ake– Type of digestive system required for digestion8/26/20132Functions of Gastrointestinal System• Digestion– Enzymatic vs. fermentation• Absorption• Protective barrier• Removal of undigested material and waste• Immunological function• Metabolism• Endocrine (hormone)Basic Organization• Arrangement of organs– Mouth– Esophagus– Stomach– Small Intestine– Large Intestine– Anus• Associated Structures– Salivary glands– Pancreas– Liver– GallbladderSize = FunctionContribute to small intestine digestion8/26/20133You are what you eat…..• Herbivore– Consume only eat plant material• Carnivore– Consume only meat• Omnivore– Consume both plants and meatForm to Function8/26/20134Basic Digestive System TypesMonogastric or Non‐RuminantBasic Digestive System TypesRuminant8/26/20135Basic Digestive System TypesMonogastric – Hindgut FermentationComparative PhysiologyStarting Simple!• Mink– Simple stomach– Short intestine– No cecum• Dog– Simple stomach– Short intestine– Small cecum8/26/20136Comparative PhysiologySimple Stomachs• Pig/Human– Simple stomach– Longer intestine– Cecum and colon sacculated• Horse– Simple stomach– Short intestine– Voluminous cecum and colonComparative PhysiologyForegut Complexity• Chicken– Complex foregut• 3 sections– Simple intestines8/26/20137Comparative PhysiologyForegut Fermentation• Sheep– Compartmentalized stomach– Long intestine– Short and simple cecum and colon• Kangaroo– Stomach sacculated and voluminous– Short cecum/colonMouth• Functions– Take in food• Prehension differs with species– Taste– Chew (masticate)• Teeth vary with species• Reduces particle size– Mix with saliva8/26/20138Mastication• Physical reduction of feed• Especially important in non‐ruminant herbivores• Adaptations– Carnivores –large canines and incisors• Tearing but little chewing– Herbivores – specialized molars• Lots of chewing and grinding• Teeth are essential for proper mastication!Structural Adaptation of Teeth8/26/20139Saliva• Functions– Lubricate feed– Start enzymatic digestion?• Species dependent– Buffer• Composition– Water– Inorganic components• Minerals• Buffer– Organic compounds• Urea• Enzymes– Amylase– Lipase• MucoproteinsProduction depends on species!050100150200Dog Sheep Horse Cattleliters/dliters/dEsophagus• Muscular tube• Pharynx to stomach (cardia)• Striated Smooth muscle• Dogs and ruminants striated throughout• Angle of attachment in horses discourages regurgitation8/26/201310Reticular Groove• Also called esophageal groove• Muscular contractions close the groove (reticulum)• Allows milk to pass from esophagus directly to abomasum– By‐passes the rumenStomach• Monogastric (non‐ruminant)– One compartment• Size varies• Ruminant– 4 compartments (3/4 of abdominal cavity)• Reticulum• Rumen• Omasum• Abomasum8/26/201311Glandular Stomach• Stomach in monogastric, abomasum in ruminants• Functions– Mixing of food– Reservoir for controlled release into small intestine– Production of HCl and pepsinogen– Limited absorption• Aspirin, alcoholStomach Anatomy• Regions:– Esophageal• Non‐glandular– Cardiac• Mucus– Fundic• Mucus• HCl (parietal cells)• Pepsin (chief cells)– Pyloric• Mucus8/26/201312Stomach Secretions• HCl – parietal cells– Denatures protein– Kills bacteria– Activates pepsinogen– Ruptures starch granules• Rennin ‐ abomasum– Clots milk• Pepsinogen – chief cells– Activated to pepsin by HCl– Pepsin starts protein digestion– Clots milkRuminant StomachGasLiquid8/26/201313Rumen Development• Only abomasum developed in newborn ruminant– Little fermentative capability• Size• Musculature• Microbial population• Development requires solid feed and microbes• 2 to 3 months of ageInfluence of Diet on Rumen Development• How does diet impact the factors involved in rumen development?– Size & musculature– Papillae development– Microbial populations8/26/201314Size of Stomach CompartmentsCattle, % Sheep, %Rumen 54 62Reticulum 7 11Omasum* 26 5Abomasum 13 22What is a pseudo‐ruminant?Function of Compartments• Reticulum– Honeyc omb appearance• Studded with small papillae– Fermentation– Traps objects• Hardware disease• Rumen– Papillae– Fermentation• Absorption of VFA, NH3, water8/26/201315Function of Compartments• Omasum– Many piles– Reduction of particle size– Absorption of water, VFA• Abomasum– “True stomach”– Similar to monogastric glandular stomach– Displaced abomasumFermentation• Occurs primarily in reticulum and rumen• Rumen microbial population– 25‐50 x 109bacteria/ml– 25‐50 x 104protozoa/ml– Yeast and fungi in smaller amounts• Products of fermentation– VFA– Gas (methane, carbon dioxide)– Heat– Microbial crude protein – B vitamins– Vitamin KSymbiotic Relationship8/26/201316Feed the Microbes,Let the Microbes Feed the Ruminant!Feed InVFAMicrobial