DIGESTIVE SYSTEMS

1. DIGESTIVE SYSTEMS ANIMAL SCIENCE 110 Fall 2001

2. CLASSIFICATION • Carnivore - simple stomach monogastric - consume animal tissue as primary nutrient source. Example: Dog & Cat. • Herbivore - consume plant tissue • Monogastric (Horse & Rabbit) • Ruminant (Cattle, Sheep & Goats) • Omnivore - consume plant & animal tissue • Monogastric (Human & Pig)

3. Digestion includes all of the processes (both chemical and physical) which break down the food into particles that can be absorbed into the blood and utilized for maintenance and productive purposes.

4. MONOGASTRIC SYSTEM • Mouth - includes teeth, lips & salivary glands. • Mastication or chewing of food plus moistening and lubrication of food prior to swallowing. • Esophagus - Tube from mouth to stomach. • Sphincter prevents backflow when stomach contracts. • Stomach - Secretion of HCl and some enzymes + mixing of food & enzymes.

5. MONOGASTRIC SYSTEM • Small intestine - Major site of nutrient absorption. Pyloric sphincter prevents backflow. • Bile, pancreatic juices are secreted into lumen. • pH increases. • Regions are called: doudenum, jejuneum & ileum.

6. MONOGASTRIC SYSTEM • Large intestine - Site of water absorption. Small intestine empties in from the side. • Blind pouch is called cecum (appendix) • Rectum and anus - muscular area used for storage of feces and defecation.

7. DEFINITIONS • Enzyme is a complex protein that speeds up a chemical reaction without being altered in the process. • Chyme is mixture of food and secretions which flow from stomach to S.I. • Fermentation is microbial conversion of food into products that can be used by host animal. Primarily bacteria and protozoa.

8. MONOGASTRIC DIGESTION • Salivary amylase - initiates digestion in mouth. • Stomach secretes HCl, mucous, pepsin and gastrin. • Pepsin breaks proteins into polypeptides. • Small intestine - duodenal cells secrete hormones which stimulate release of bile and pancreatic enzymes.

9. MONOGASTRIC DIGESTION • Lipase hydrolyzes fats into fatty acids and glycerol. • Trypsin & Chymotrypsin convert proteins and peptides into amino acids. • Amylase converts starch to disaccharides and monosaccharides. • Absorption of molecules is both active and passive. Blood carries nutrients to liver.

10. RUMINANT SYSTEM • Mouth includes teeth, tongue and saliva but no salivary amylase. • Esophagus is same as monogastric. • Stomach has four distinct compartments. • Rumen is the largest in the mature animal. • Reticulum (honeycomb) • Omasum (many plies or leaves) • Abomasum is similar to monogastric stomach.

11. RUMINANT SYSTEMRELATIVE PROPORTIONS Birth 2 mo. Maturity Rumen 80% 30% 70% Reticulum 5% Omasum 8% 70% 30% Abomasum 7%

12. RUMINANT SYSTEM • Small intestine, large intestine, rectum and anus have similar functions as monogastric. • Newborn ruminant is essential a monogastric for the first few weeks. A well developed esophageal groove allows milk to bypass rumen & move direct to abomasum. • Regurgitation and remastication of food (cud chewing) is important. • Neutral pH means no “heartburn”.

13. RUMEN FERMENTATION • The anaerobic (CO2) system is ideal for microbial fermentation - moist, warm and continual supply of substrates. • Microbes can digest cellulose as well as starch and soluble carbohydrates and ferments them into Volatile Fatty Acids. • Acetic, Proprionic, Lactic & Butyric acids • VFA furnish 60% to 80% of energy needs for a mature ruminant.

14. RUMEN FERMENTATION • VFA are absorbed across rumen wall and are carried to liver by blood. • Proteins in rumen are broken into peptides and amino acids. • Deamination results in free ammonia (NH4) + carbon skeleton. • Microbes resynthesize amino acids for their own cell walls and cell structures.

15. RUMEN FERMENTATION • Non Protein Nitrogen (NPN) such as urea is hydrolyzed into NH3 + CO2. • If adequate carbon substrate is present, the free NH3 can be incorporated into microbial protein. • Urea is 45% N = 281% crude protein equivalent. ( 45% x 6.25 = 281%) • B vitamins are also synthesized in rumen.

16. RUMEN FERMENTATION • Gases (carbon dioxide and methane) are primary byproducts of rumen fermentation. • Usually these gases are eructated or belched out. If not bloat occurs. • Bloat is a severe distension of the left side of the ruminant and can result in death.

17. RUMEN FERMENTATION • After fermentation, undigested feed particles, bacteria, protozoa and fluid move to the abomasum and become “food” for digestion. • Microbial protein is a fairly well balanced protein source for the ruminant.

18. PROTEIN AS ENERGY • Excess protein and amino acids can be used as an energy source in both monogastrics and ruminants. • The amino acids are deaminated and the ammonia is excreted in urine. • Protein is a more expensive energy source than carbohydrates or fat. • We attempt to feed protein to meet but not exceed the requirement.

19. HORSE DIGESTIVE SYSTEM • Similar to monogastric system prior to the large intestine with two exceptions. • Esophagus joins stomach at an oblique angle so that horse cannot belch out gas or chew a cud. • Horse has no gall bladder. Bile is released directly from liver to small intestine.

20. HORSE DIGESTIVE SYSTEM • Caecum and colon in large intestine have extensive fermentation. • Microbial fermentation of fiber and any soluble carbohydrates that escape absorption in small intestine can be fermented. VFA are 25%+ of total energy. • Microbial protein and B vitamins are produced but absorption is less efficient.