39. Nutrition

CHAPTER 39. Nutrition

Rebecca S. McConnico




BASIC BACKGROUND REGARDING EQUINE NUTRITION






I. Nonruminant herbivore


II. Hindgut fermenter


III. Horses can utilize high-fiber roughages as a source of nutrition, for example, grass or leguminous hays


IV. Horses can utilize high-quality concentrate feeds as well


V. Because horses are marketed or enjoyed as athletes, many nutritional strategies target their athleticism


BASIC EQUINE GASTROINTESTINAL ANATOMY RELATED TO NUTRITION






I. Mouth




A. Equine upper lip is used for prehending food (gathering food bolus, grass, or grain)


B. Upper incisors are used for cropping grass from pasture or hay portion


C. Molars are important for grinding the feedstuffs (cracks fibrous feed coats)


D. Muscles face, tongue, and jaws are used for chewing and masticating a food bolus within the oropharynx


E. Cranial nerve (CN) V (trigeminal nerve) innervates the muscles of mastication


F. Ensalivation is the process of moistening the food in the oropharynx


G. Saliva production per horse in 24 hours + ∼ 5-6 L/100 kg body weight


H. The food bolus is swallowed via innervation of CN IX, X, and XII (glossopharyngeal, vagus, and hypoglossal)


J. Dysfunctions in swallowing can result in two major complications


K. Esophageal obstruction (also known as “choke”)


L. Tracheal aspiration can lead to aspiration pneumonia; aspiration pneumonia can lead to serious life-threatening disease if not treated appropriately


M. Injury or disease of any of these structures can affect the horse’s ability to gather or use feed


II. Stomach




A. Small size reflects evolution of the horse as a nibbler (eats continually)


B. Holds ∼8 L and makes up ∼8% of the total size of the digestive tract


C. Relative rate of feed passage in equine stomach is rapid


D. Small amount of enzymatic and microbial digestion begins in the equine stomach


III. Small intestine




A. Primary site of enzymatic digestion, especially when diets high in concentrate are fed


B. Proteins (polypeptides)




1. Broken down by nonspecific oligopeptidases (brush border enzymes)


2. Individual amino acids and dipeptides are absorbed


3. Some via pancreatic enzymes


4. Brush-border enzymes


5. Requires sodium as cotransporter


C. Carbohydrate digestion: Specific enzymes




1. Sucrase, lactase, maltase


2. Require sodium as transporter


3. Pancreatic amylase: Hydrolyzes starch into disaccarides and trisaccharides for absorption


D. Fats are emulsified in the small intestine and require pancreatic and biliary secretions




1. Pancreatic lipase + triglycerides yield β-monoglycerides and free fatty acids, which are solubilized by bile salts and taken up by the enterocyte into the lymphatics


2. Bile salts are taken up by active transport back to the liver (ileum)


3. Fatty acids are absorbed as micelles, then re-esterified to triglycerides within the enterocyte


4. Released as chylomicrons into lymphatics as complexes of cholesterol, phospholipids, and a protein coat


5. Entire process is passive


E. Absorption of water occurs in the equine small intestine




1. Via diffusion down concentration gradient


2. Between cell tight junctions


3. Through cells → apical to basolateral


4. Can also go from plasma to lumen


F. Sodium and water transport occurs in the equine small intestine




1. Chloride transport is via passive transport through the tight junction


2. Is carrier-mediated, electrically neutral, with Na+ cotransport


G. Bicarbonate transport (HCO3-) – is dumped from liver and pancreas directly into the intestine:




H + + HCO 3−→H 2CO3→CO 2+H 2O

CO 2 equilibrates within epithelial cells and venous blood


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Apr 6, 2017 | Posted by in GENERAL | Comments Off on 39. Nutrition

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