Equine Digestive System PDF

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Equine digestive system...

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The digestive system starts with the oral cavity and ends at the anus o Also called the digestive tract, alimentary canal, or alimentary tract Anatomy of the digestive tract o Oral cavity  Lips  Large, prehensile  Allow the horse to be selective  Pick up, segregate, and separate very small particles  Teeth  Horses have upper and lower incisors  Assist in grazing grass to shorter lengths  Premolars and molars grind food and form a bolus  Condition of the teeth reflect the animal's ability to fully utilize nutrients in feed  Tongue (lingua)  4 types of taste papillae  3 muscle groups  Used for grooming, manipulation of food in the oral cavity, deglutition reflex and vocalization  Not used for prehension  Selectivity  Taste and smell play a role in feed selection and intake  Distinguish difference in flavor  Preference for sweet  Differentiate textures  Favorite flavors:  Fenugreek, banana, cherry, rosemary, cumin, carrot, peppermint, oregao  Salivation and ensalivation  Major functions of saliva:  Assists in deglutition-lubricates the food bolus  Limits voluntary feed intake  Buffers stomach acid  Suckle seal  No psychological stimulation  Food must be present in the mouth  Parasympathetic stimulation  High volumes of dilute saliva lubricate mucus membranes  Small amounts of viscous mucoid saliva  Equine saliva:  99% water, nearly no enzymes  Horses can produce 10-35 liters of saliva/day  Cf: bovine 150L/day o Esophagus  Extends from the pharynx to stomach  Proximal striated muscle, distal smooth muscle  Conveys food boluses from the pharynx to the stomach

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Opening of the stomach from the esophagus is controlled by the cardiac sphincter  Prevents gastric reflux  Prevents eructation of gases A horse cannot vomit Rarely eructate Do not chew cud Fore gut Stomach  Accounts for 5% of the digestive tract  Holds 2-4 gallons  Passage of ingesta from the stomach is regulated by pyloric sphincter  Passage rate reported from 15-300minutes  Liquids and large meals pass faster  Primary function: comminution and acid digestion  Digestion  HCl breaks down feed  Into starch, fiber, fat, and protein  Pepsinogen breaks down protein into amino acids Small intestines  Extends from the pylorus of the stomach to the caecum  Relatively small for the size of the animal  Holds 12-20 gallons  60-75 feet long  Transit time  90-300 minutes  Large particles faster than small  Roughage faster than concentrate  Components  Duodenum- muscular peristalsis and pancreas attachment  Jejunum- digestive and absorptive  Ileum-muscular peristalsis  Terminates at the ileocaecocolic junction  Function: enzymatic digestion  Breakdown and absorption of:  Sugar, starch, and lipids  Amino acids  Ca, P, B12  Fat soluble vitamins (A, D, E, K) Hind gut Cecum  Major component of equine digestion  Function: microbial fermentation  Microbiota-primarily bacteria but some fungi and lesser protozoa  Break down starches and cellulose to SCFA's or VFA's  30-70% of a horses DE from VFA's  Acetate

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Propionate Butyrate  Increasing volumes of NSC's favor lactate and propionate at the expence of acetate  Size and passage rate  4 feet long  7-9 gallons  5-6 hours  Large colon  Several segments  RVC- right ventral colon, LVC, LDC, RDC and the transverse colon  Function  Fermentation and nutrient absorption  VFA's, vitamins and minerals  Size/volume  40% of digestive tract  8-12 feet long  14-24 gallons  Passage rate  36-48 hours or more  Greatly influenced by feed particle size, hydration status, nutrient density and outflow from the small intestine and cecum  Small colon  Function: water and mineral absorption  Size/volume  10% of digestive tract  10-12 feet  5 gallons  Passage rate  variable  Rectum  Function: storage and expulsion of feces  Size  10-14 inches and holds 2-4 gallons GI tract parts and function o Oral cavity  Mastication, insalivation, deglutition o Stomach  Liquification, acid degradation, and comminution o Small intestine  Enzymatic digestion and CHO, AA, and fat absorption o Cecum  Fermentation of forage to VFA's o Large colon  Fermentation and absorption of VFA's, vitamins, and minerals o Small colon  Absorption of nutrients and water

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Rectum  Absorption of water and fecal ball formation Digestion through the GI tract o Oral cavity  Mastication and ensalivation o Esophagus  Uni-directional peristalsis o Stomach  Uni-directional rhythmic contractions  Very little microbial fermentation  Constant gastric acid secretion for comminution, digestion, and liquifaction o Duodenum  Muscular peristalsis o Jejunum  Enzymatic digestion and nutrient absorption o Ileum  Muscular peristalsis regulates cecal filling o Cecum  Microbial fermentation o Ascending colon  Microbial fermentation  Nutrient absorption o Descending colon  Water absorption o Rectum  Waste evacuation...