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Equine Science Digestive Physiology The Digestive Tract Horses are non-ruminant herbivores “simple stomach” animal Utilize 1 stomach Able to utilize large amounts of roughage due to their relatively large cecum Cecum is a section of the colon where digestive bacteria break down roughage The Digestive Tract The 5 functions of the digestive system are: Ingestion Grinding Digestion Absorption of nutrients Elimination of waste Mouth Mouth- first part of digestive system. Mouth has 2 main functions- masticate food and breakdown food with saliva. Functions of Saliva: Digest buffer for pH Moisten mouth Aids in taste Teeth Top and bottom bridge. Should be examined by professional to check for sharp edges that must be floated or filed down Breakdown feedstuff mechanically Digestive tract cont. The esophagus- 50- 60 inches long in an adult horse. Muscular tube that extends from the pharynx to the cardia of the stomach Horses have striated muscles in the beginning, and smooth muscles at the end of the esophagus. Digestive tract cont. Sphincter - one way door that allows food to come in to the stomach, but not out. Stomach may actually rupture before animal will vomit. Once in the stomach, the matter in considered “digesta” Stomach Cont. Stomach- relatively small. Therefore horses should be fed several small meals per day. Should feed by volume not weight! Stomach - made up of 4 layers Serosa (outer) Muscularis Submucosa Mucosa (inner) Stomach Cont.. Mucosa is the most inner layer, it is a muscle Muscle contractions causes the digesta to mix with Chemicals and enzyme secretions Mucus - functions to protect muscles from hydrochloric Acid (HCL), and aids in digestion. Hydrochloric Acid (HCL) - aids in digestion, 1st form of chemical digestion, kills bacteria Stomach Cont.. 5 Regions Cardia - sphincter region Esophageal - non glandular Cardiac- produces and secretes mucus Fundic- produce HCL and mucus, also produces pepsin and rennin Pyloric - Secretes Prodeolytic enzymes, sphincter muscle as well Small Intestine (SI) Also known as the “upper gut” The Small Intestine- contains 30% of the capacity of the entire tract. Digesta in the small intestine is 93-95% liquid. Most digestion and absorption takes place in the small intestine Small Intestine The same layers in the stomach are present in the intestine. Mesentery - membrane that holds the lymphatic and blood vessels to the intestine Small Intestine Mesentery Small Intestine The rate of passage is rapid through the SI. Grinding or chopping feed will increase the rate of passage, therefore decreasing???? Absorbs soluble carbohydrates (CHO) Soluble Small Intestine Lumen- folds inside the small intestine. Villi - fingerlike projections on the lumens Increase surface area Microvilli - fingerlike projections on the villi that absorb nutrients Small Intestine Villi and Microvilli Small Intestine There are 3 parts to the small intestine. Duodenum Jejunum Ileum Small Intestine Duodenum (longest portion) The pancreatic duct (pancreas) and bile duct (liver) empty digestive juices into the duodenum A majority of absorption of nutrients occurs in this section. Extends to the pelvic region, along the lower right side of the animal. It then crosses over to the left and turns back to the head Small Intestine Jejunum and Ileum A lower percentage of absorption takes place in these 2 regions of the small intestine The only way to differentiate the different regions of the small intestine is through a microscope. Absorption Proteins, CHO, fats, minerals and vitamins are all digested in the small intestine Water is absorbed in the large intestine Absorption Methods Passive Diffusion = requires no energy Active Transport = requires energy Passive Transport = requires a carrier to get across membrane Large Intestine Also known as the “hind gut” Composed of Cecum, colon (large and small), and rectum Horses have the largest and most complex LI in domesticated animals, due to their large cecum Functions to move undigested material from the SI to the anus for elimination Makes up about 50 percent of the total capacity of the digestive tract. Large Intestine Approximately 25 feet long Can digest cellulose, starch, and sugars into volatile fatty acids The horse's large intestine is designed to utilize plant fiber. Volatile fatty acids - Acetic, buteric, and propionic acids that are produced by microbial digestion of CHO This VFA can supply up to 1/4 of the energy used by the horse Large Intestine Vitamins E and K are synthesized in the large intestine. These are fat soluble vitamins. Bacteria in the LI produce some amino acids, but mostly fatty acids Fatty acids = energy Amino acids = protein synthesis Large Intestine Cecum - primary water absorption site. Fermentation occurs in the cecum, similar to the action that takes place in the forestomach of the ruminant Rate of passage through the LI is relatively slower than other parts of the digestive tract. Large Intestine Rectum Connects the small colon with the anus. Receives feces from the small colon, which formed the characteristic balls of horse manure. Reabsorbs water that was not absorbed in the cecum. Large Intestine Feces The size, shape, and consistency of feces give an indication of the general health of the horse. If the feces is hard and dry, then the horse may be deficient in water or protein. If the feces is moist or soft, the horse may be sick or consuming a diet that is too laxative. Rate of passage 95% of all food eaten will be excreted in the form of feces within 65-75 hours of ingestion Factors Affecting Digestion Processing of feedspellets require less digestion than whole grains. Feed processing Grinding feed speeds rate of passage therefore decreasing absorption. Feed Processing Crimping oats will increase rate of digestion. Factors affecting Digestion cont. Level of intake- the more grain eaten, the less digested Frequency of feeding- frequent feeding can increase level of digestion. Terminology to know Non- Ruminant Roughage Ingestion Digestion Mouth Teeth Esophagus Pharynx Stiated muscle Smooth muscle Peristalsis uppergut hindgut mesentery CHO HCL pepsin rennin Terminology to know Sphincter Lumen Villi Microvilli Absorption methods (3) Volatile Fatty acids Amino Acids Fat soluble vitamins Digesta Saliva