Equine Science

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Equine Science

• Digestive Physiology

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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

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The Digestive Tract

• The 5 functions of the digestive system are
• Ingestion
• Grinding
• Digestion
• Absorption of nutrients
• Elimination of waste

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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

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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

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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.

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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

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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)

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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

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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

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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

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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

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Small Intestine

• Mesentery

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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

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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

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Small Intestine

• Villi and Microvilli

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Small Intestine

• There are 3 parts to the small intestine.
• Duodenum
• Jejunum
• Ileum

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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

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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.

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Absorption

• Proteins, CHO, fats, minerals and vitamins are
  all digested in the small intestine
• Water is absorbed in the large intestine

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Absorption Methods

• Passive Diffusion requires no energy
• Active Transport requires energy
• Passive Transport requires a carrier to get
  across membrane

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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.

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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

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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

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Large Intestine

• Cecum - primary water absorption site.
• Fermentation occurs in the cecum, similar to the
  action that takes place in the fore-stomach of
  the ruminant
• Rate of passage through the LI is relatively
  slower than other parts of the digestive tract.

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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.

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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.

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Rate of passage

• 95 of all food eaten will be excreted in the
  form of feces within 65-75 hours of ingestion

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Factors Affecting Digestion

• Processing of feeds- pellets require less
  digestion than whole grains.

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Feed processing

• Grinding feed speeds rate of passage therefore
  decreasing absorption.

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Feed Processing

• Crimping oats will increase rate of digestion.

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Factors affecting Digestion cont.

• Level of intake- the more grain eaten, the less
  digested
• Frequency of feeding- frequent feeding can
  increase level of digestion.

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Terminology to know

• Non- Ruminant
• Roughage
• Ingestion
• Digestion
• Mouth
• Teeth
• Esophagus
• Pharynx
• Stiated muscle

• Smooth muscle
• Peristalsis
• uppergut
• hindgut
• mesentery
• CHO
• HCL
• pepsin
• rennin

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Terminology to know

• Sphincter
• Lumen
• Villi
• Microvilli
• Absorption methods (3)
• Volatile Fatty acids
• Amino Acids

• Fat soluble vitamins
• Digesta
• Saliva