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The Equine Digestive System Objectives Discuss internal organs Identify the structures of the digestive system Recognize functions of the organs comprising the digestive system Digestive System Monogastric - having one stomach Herbivores - plant-eating animals Digestive system anatomically developed to continually digest small amount of food Digestive System Eat simple-looking feeds containing complex chemical substances dramatic changes during digestive process before feed is used as energy Digestion - process of mechanical and chemical breakdown of feed into simple structures Digestive System Simple structures are: soluble (able to be dissolved) in water absorbed through mucous membranes lining intestinal tract membranes that line cavities in the body and connects inside of cavity to outside Digestive System Unique Small, efficient stomach for grain utilization Large cecum and colon for roughage utilization Digestive System Purpose - process feed into component nutrients for: Absorption - process of taking in by various means Utilization Digestive System Alimentary canal (digestive system) muscular hollow tube beginning at mouth and ending at anus Loops on itself many times Size - One inch in diameter at small intestine to eight inches at large colon Digestive System Component parts include: Mouth Pharynx Esophagus Stomach Small intestine Large intestine Rectum Anus Digestive System Digestive System Large intestine consists of the: Cecum Ventral and dorsal colon Transverse colon Small colon Rectum Digestive System Alimentary tract with help of teeth, tongue, salivary glands, liver, and pancreas prepare feed for absorption and eliminates waste Few feeds eaten are in simple forms ready to be absorbed and utilized Digestive System Most feeds require substantial change by: Mechanical Action Secretory Action - products produced by glands that aid in digestion Chemical Action Microbial Action - digestion by very minute organisms Digestive System Mechanical actions include: Mastication – chewing Deglutition – swallowing Intestinal movements Defecation - elimination of waste Anatomy of the Digestive System Mouth First section of alimentary canal Contains 24 molars and 12 incisors Includes tongue and salivary glands Mouth Prehension -the grasping and moving of feed into the mouth by a sensitive, mobile upper lip Precise - can graze grass almost into ground Sorts and selects hay Mouth Digestion - begins in mouth when feed is masticated by the teeth grinded and chewed by the mouth Serves to reduce feed particle size Mouth Saliva: 85 pounds (10 gallons) daily Wets feed - Easier to pass through esophagus Enzymes - help digest carbohydrates Produce large amounts only while chewing Pharynx Muscular Funnel shape Guides feed into esophagus Located in upper back of mouth where digestive and respiratory tracts cross Pharynx Once feed or water enters pharynx, it cannot return because of blocking action of soft palate Epiglottis closes at the same time to prevent feed from entering lungs Esophagus 4 to 5 feet in length Extends from mouth down left side of neck, through the diaphragm, and to the stomach Moves feed and water to stomach by progressive waves of muscular contractions called peristalsis Esophagus Waves irreversible Extreme muscle tone occurs at end of esophagus Esophagus Extremely difficult to expel gases through eructation the act of expelling gas from the stomach through the mouth Stomach would rupture before vomiting would occur Stomach U-shaped sac near diaphragm at front of abdominal cavity Sphincter acts as powerful muscle where esophagus enters into stomach Makes vomiting nearly impossible Stomach Small compared to other animals 10% of total capacity of entire digestive tract Capacity - two to four gallons requires they eat two to three times daily rather than just once Stomach Feed moves through rapidly Frequent feeding in small amounts is more efficient and better satisfies Rate of passage is rapid in comparison to other areas Time required for something to move through an area Stomach Reservoir for ingested feed while subjecting it to gastric digestion chemical breakdown of feedstuffs by the stomach Gastric juices, secreted by glands in the mucous membrane of stomach, contain hydrochloric acid, pepsin & gastric lipase Stomach Pepsin is a protease - enzyme that helps digest protein into amino acids building blocks of proteins Gastric lipase - digest fat into fatty acids & glycerol Stomach When two-thirds full, feed passes into small intestine and continues as eating continues If horse eats too much at one time, some will leave stomach without sufficient digestive action Leads to decreased efficiency Stomach Number of digestive disorders can occur Caused by: moldy feeds ground mashes sudden changes in feed feast-and-famine situations parasites Stomach Very little nutrient absorption takes place in the stomach Proteins and carbohydrates are only partially digested Small Intestine 2 inch by 60 foot tube Holds approximately 12 gallons Connects stomach to large intestine Contains three parts: the duodenum, the jejunum, and the ileum Small Intestine 30% of the digestive tract Folded into many loops and coils 2.5 to 4 hours for feed to pass Small Intestine Bloodworms cause blood clots may result in colic or death tend to lodge in the mesentery artery which supplies blood to the intestines Small Intestine Small intestine and accessory organs, the pancreas and liver, supply enzymes Peristalsis mixes fluid contents of the which are about 92-95% water Pancreatic juices contain the enzymes trypsin, pancreatic lipase, and amylase Small Intestine Trypsin - converts proteins into amino acids which the small intestine absorbs Primary site of protein digestion and absorption of amino acids Pancreatic lipase - breaks down fats to glycerol and fatty acids Small Intestine Liver secretes bile helps break down fat aids in fatty acid absorption activates pancreatic lipase Most soluble carbohydrates digested in small intestine Small Intestine End products of carbohydrate digestion are glucose and volatile fatty acids which are absorbed for energy Absorbs nutrients, such as simple sugars, fatty acids, amino acids, minerals, and vitamins Large Intestine Composed of the cecum, large colon, small colon, and rectum Moves undigested materials from small intestine to anus for elimination 50-60% of digestive tract Large Intestine Holds 30-35 gallons 25 feet long Designed for utilization of plant fiber for energy Large Intestine After ingesta leaves small intestine, it enters into cecum substances that have been taken into the body by way of the digestive tract Cecum serves as fermentation vat in which enzymes break down fibrous plant structures for digestion Large Intestine Carbohydrates such as cellulose that escaped digestion in small intestine are fermented in large intestine Complex carbohydrate that is the main component of the plant cell wall Large Intestine Can digest cellulose, starch, & sugars into volatile fatty acids supplies up to 25% of horse’s energy Large Intestine Cecum - primary site of water absorption Rate of passage slower than in other portions of digestive tract 36-48 hours Rectum Connects small colon to anus Receives feces small colon has formed into characteristic balls Forty to fifty pounds of feces is voided eight to twelve times a day Rectum Shape, size, and consistency of feces give clues to overall health Dry and hard - lack of water or protein Too soft - Sick or eating diet that is too laxative Digestive System Disorders Disorders Because of the complex nature of the digestive system, horses are predisposed to digestive disorders Susceptible to twisting and impaction of the large intestine Disorders Sensitive to gases produced by microbial digestion Rapid fermentation may cause excessive gas or lactic acid to be produced can cause colic or laminitis Colic “Colic” - many painful digestive disturbances with various causes Improper feeding such as feeding too much grain or suddenly changing the diet can cause colic Colic Usually caused by gaseous products that are part of microbial digestions May cause swelling in digestive tract Ingesting low quality, poorly digestible feed can cause impaction of cecum and colon Colic To avoid digestive disturbances, allow one to two weeks to change from one feed to another. Laminitis Occurs when inner hoof wall becomes inflamed Rapid changes in diet can cause certain type of bacteria in cecum to die Release large amounts of endotoxins Laminitis Endotoxins enter bloodstream and decrease the amount of blood flow to lamina Commonly occurs when a horse is switched from winter hay to pasture in the spring Summary Purpose of digestive system is to process feed into component nutrients for absorption and utilization by the body Very complex Many digestive disorders Summary Monogastric Eat relatively simple-looking foods that are transformed to an easily digestible form ALL RIGHTS RESERVED Reproduction or redistribution of all, or part, of this presentation without written permission is prohibited. Instructional Materials Service Texas A&M University 2588 TAMUS College Station, Texas 77843-2588 http://www-ims.tamu.edu 2008