Digestive Systems

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Digestive Systems

• Chris Ellason

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Digestion and Absorption

• The process of digestion includes
• The prehension of food or feed
• The mechanical chewing and grinding
• Mixing with digestive acids and enzymes to
  chemically break down feedstuffs
• The process of absorption includes
• Transport of the digested foods across the
  intestinal mucosa to the blood or lymph system

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General Terms

• Prehension to take into the mouth
• Mastication chewing
• Deglutition swallowing
• Regurgitation the backward flow of food through
  the esophagus

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Three Major Categories

• Carnivore consume flesh of other animals,
  examples are dogs and cats
• Omnivore consume both plants and flesh, examples
  are primates
• Herbivore consume plant material, examples are
  horses and cattle

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Carnivore

• Very Well developed stomach
• Uncomplicated intestine
• Limited fiber digestion

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Omnivore

• Combination of carnivores/herbivores
• More complicated GIT than carnivores
• Colonic digesters
• Pigs, humans
• Cecal digesters
• rat

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Herbivore

• Cow, horse, rabbit
• Each has a different type of GIT
• Cow- ruminant
• Horse- simple stomach, large cecum, large
  sacculated LI
• Rabbit- larger stomach, very large sacculated
  cecum, unsacculated LI

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Salivary Glands

• 3 pair
• Parotid
• Mandibular
• Sublingual
• Water - moistens food aids in swallowing
• Mucin - lubrication for swallowing
• Bicarbonate salts
• Enzymes

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Salivary Glands
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Salivary glands
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Different Digestive Tracts

• Farm animals have a variety of digestive systems
• Ruminants have 4 different compartments to the
  stomach
• Examples include cattle, sheep, goats
• Nonruminants (also known as monogastrics)
• Hogs, dogs, and cats have a single, simple
  stomach
• Poultry have a two part stomach
• Horses have a large, functional cecum

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Pregastric vs Postgastric

• Pregastric Fermentation that occurs in the rumen
  of ruminant animals. It occurs before food passes
  into the portion of the digestive tract in which
  digestion actually occurs.
• Postgastric The fermentation of feed occurs in
  the cecum, behind the area where digestion has
  occurred.

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Pregastric vs Postgastric

• Ruminants
• More efficient
• Less intake
• Non- ruminant herbivores
• Only postgastric
• Less efficient
• Greater intake

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Monogastric Systems

• Mouth prehension and chewing of food some
  carbohydrate enzyme activity
• Esophagus
• Stomach
• Storage
• Muscular movements (break down food)
• Secretes Digestive Juices (hydrochloric acid)
• pH about 2

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Monogastric Systems
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Small Intestine

• Duodenum
• Active Digestion Site
• Produce enzymes
• Pancreas
• Helps to neutralize ingesta entering the SI
• Liver
• Produces bile breaks down fats
• Intestinal Walls

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Small Intestine

• Jejunum
• Active in nutrient absorption
• Ileum
• Active in nutrient absorption
• Villi
• pH 6 to 7

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Large Intestine

• 3 Sections
• cecum
• colon
• rectum
• Active in water resorption
• Secretion of some minerals
• Bacterial Fermentation

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Horses are Different

• Saliva
• contains no enzymes
• may secrete up to 10 gallons/day
• stimulated by scratching
• Esophagus
• only one way peristaltic movement
• Impossible for regurgitation

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Horses are Different

• Stomach
• much smaller in comparison to other species
• not very extensive muscular contraction
• So how should we feed differently?
• Small Intestine
• same as pig but no gall bladder
• Cant handle a high fat diet

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Horses are Different

• Large Intestine
• over 60 of GIT
• 4 parts
• cecum
• large colon
• small colon
• rectum

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Cecum and Large Colon

• Similar to Rumen
• bacterial cellulose breakdown
• bacterial protein breakdown
• VFA production
• Water Soluble Vitamin production

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Small Colon and Rectum

• Primary site for water resorption
• Can become impacted with feed

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Horse GI Tract
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Avian Species

• Beak
• no teeth
• can be used to reduce particle size
• Esophagus
• ingesta holding and moistening
• Salivary Amylase
• Fermentation in some species

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Avian Species

• Proventriculus
• Gastric juice production
• pH 4
• Rapid pass through of food

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Avian Species

• Gizzard (ventriculus)
• thick muscular wall
• particle size reduction (similar to mastication)
• nonglandular
• normally contains grit
• no enzymatic secretion

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Avian Small Intestine

• Functions in digestion and absorption of feed and
  nutrients just as in other monogastrics
• pH is slightly acidic
• Most enzymes found in mammals except?

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Avian Large Intestine

• Contains 2 blind pouches instead of ?
• Mostly water absorption
• Some bacterial activity but less than in most
  mammals
• very short in comparison

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Avian Species
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Ruminant Digestive System

• Mouth
• what is unique about the teeth?
• Can only chew on one side of mouth at a time
• Saliva production is continuous
• Production about 12 gallons/d

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Rumen Stomach

• 4 PARTS
• reticulum
• rumen
• omasum
• abomasum

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Reticulum

• Honeycomb
• most cranial
• not truly separated from rumen
• no enzymatic secretion
• walls are tough, tend to catch heavy objects

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Rumen

• Large compartment extends from diaphragm to
  pelvis
• papillae
• Fermentation chamber
• Majority of absorption of byproducts and
  conversion to volatile fatty acids

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Rumen Digestion

• Reticulorumen provides a favorable environment
  for bacterial fermentation
• Continuous turnover of digesta and removal of
  fermented digesta
• Anaerobic fermentation

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Omasum

• Manyplies (Stockmans Bible)
• short blunt papillae
• very muscular
• no enzymatic secretion
• reduction of particle size
• water resorption

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Abomasum

• True Stomach
• First Glandular portion of the tract
• Very similar in structure and function to
  nonruminant stomach

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Other Unique Points

• Esophageal Groove
• cardia to omasum
• milk bypass
• Rumination The process where rumen contents are
  regurgitated, remasticated, and reswallowed for
  further digestion
• Eructation expulsion of accumulated fermentation
  gases from rumen via esophagus

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Ruminant GI Tract
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Rumination

• Regurgitation of ingesta with mastication
• reticular contraction that concentrates ingesta
  at the cardia
• increased inhalation of air at same time
• contraction of diaphragm
• ballooning of esophageal walls
• ingesta sucked into esophagus
• returned to mouth by reverse peristalsis

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Rumination

• Excess liquids are swallowed
• Mastication commences
• More time spent masticating here than initial
  intake
• Amount of time ruminating is a function of diet
  composition

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Rumen Contents and Motility

• Rumen contents are not uniform
• Occur in stratified layers
• Change from ventral to dorsal
• Rumen mat
• high concentrate diets eliminate mat
• more viscous fluid in high grain diets
• lowest dry matter in high forage diets

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Rumen Contents and Motility

• Motility of rumen mixes contents
• Divided into
• primary contractions
• secondary contractions
• Contractions require up to 50 seconds to complete

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Rumen Contents and Motility

• Contractions begin with reticulum
• Progress dorsally
• Finish with ventral blind sac and ventral pillars

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Rumen and Acute Acidosis

• Optimal rumen pH is 6.7
• Variation in pH is normally /- 0.5
• Introduction of high grains result in
• breakdown of rumen mat
• proliferation of facultative anaerobes
• these produce high levels of lactic acid

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Rumen and Acute Acidosis

• Lactate is a much stronger acid that other VFAs
• In severe cases lactate can make-up well over 50
  of total rumen acids
• Succinate and Formate can also appear in high
  quantities

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Rumen and Acute Acidosis

• Increased acids can reduce pH as far as 4.0
• Severe rumenitis occurs at these pH levels
• Absorption of lactic acid results in systemic
  acidosis
• All chronic acidosis results in rumen
  parakeratosis

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Factors Affecting Digestibility

• Rate of passage increased rate of passage of
  digesta through the tract reduces digestibility
• Factors increasing rate of passage include
• Increased level of feeding/intake (ruminants)
• Finer processing (such as grinding) of feed
• Note grinding grain usually increases
  digestibility but grinding hay decreases
  digestibility