Anatomy of the Ruminant Digestive Tract

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Anatomy of the Ruminant Digestive Tract

• References
• D. C. Church. The Ruminant Animal Digestive
  Physiology and Nutrition
• Chapter 2. Anatomy of the gastro-intestinal
  tract
• Chapter 3 (pp 46-62). Normal stomach development
• Chapter 4 (pp 85-94). Rumination and Eructation
• Chapter 6. Salivary function and production

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GI tract fermentation

• Pregastric

• Large Intestinal

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Advantages of pregastric fermentation

• Make better use of alternative nutrients
• Cellulose
• Nonprotein nitrogen
• Ability to detoxify some poisonous compounds
• Oxalates, cyanide, alkaloids
• More effective use of fermentation end-products
  including
• Volatile fatty acids, microbial protein, B
  vitamins
• Decrease in handling undigested residues
• In wild animals, it allows animals to eat and run

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Disadvantages of pregastric fermentation

• Fermentation is inefficient
• Energy
• Loss Amount ( of total
  caloric value)
• Methane 5-8
• Heat of fermentation 5-6
• Protein
• Protein
• Some ammonia resulting from microbial degradation
  will be absorbed and excreted
• 20 of the nitrogen in microbes is in the form of
  nucleic acids
• Ruminants are susceptible to ketosis
• Ruminants are susceptible to toxins produced by
  rumen microbes
• Nitrates
  Nitrites
• Urea
  Ammonia
• Nonstructural carbohydrates Lactic acid
• Tryptophan
  3-methyl indole
• Isoflavonoid estrogens estrogen
• Coumestans

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Classes of ruminants

• Concentrate selectors
• Very selective
• Limited fiber digestion
• Intermediate feeders
• Seasonally adaptive
• Roughage grazers
• Nonselective grazers
• Good ability to digest fiber

Common Duiker, Deer
Goats, Sheep, Moose
Cattle, Bison
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The ruminant digestive tract

• Lips
• Range from short, relatively immobile in
  nonselective grazing species to very mobile
  (prehensile) in selective grazing or concentrate
  selecting species

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Ruminant teeth

• Dental formula for cattle and sheep
• Jaw
• Upper Lower
• Incisor 0 4
• Canine 0 0
• Premolar 3 3
• Molar 3 3
• Upper jaw is wider than lower jaw

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Tongue

• Uses
• Aid in chewing and forming boluses
• Aid in drinking
• Prehension of feed
• Covered with rough, hook-like (filiform) papillae
  that assist in grasping feed
• Important in nonselective grazing species
• Taste
• Taste buds
• More numerous than monogastric species
• More numerous on nonselective grazing species
• Primarily used for food avoidance

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Salivary glands

• 7 groups of glands located around the mouth
• ½ of total saliva from the paired parotid glands
• Functions
• Enzymes
• No amylase
• Pregastric esterase in young
• Moistens and lubricates feed
• Water balance
• Bloat prevention
• Recycling of N and minerals including Na, P, and
  S
• A 700 kg dairy cow fed a hay-grain diet will
  secrete
• 190 l saliva/day containing
• 30-80 gm total N
• 1100 gm NaHCO3
• 350 gm Na2HPO4
• 100 gm NaCl
• Buffer secretion
• Normal rumen, pH 5.5 7.0
• Without salivary buffers, pH 2.8 3.0

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Factors affecting saliva secretion

• Dietary fiber concentration
• Forage to grain ratio of the diet
• Maturity of the forage
• Diet particle size
• Grinding
• Grain processing by-products
• Diet moisture level

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Consequences of inadequate effective fiber in
ruminant diets

• Reduced rumination
• Reduced rumen pH
• Reduced fiber digestion
• Altered fermentation pattern
• Milk fat depression
• Lactic acidosis
• Ruminal parakeratosis
• Reduced microbial protein production in rumen
• Increased hydrogen sulfide production in the
  rumen in animals fed high sulfur diets

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Pharynx

• Structure similar to monogastrics
• Involved in rumination and eructation

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Esophagus

• Mucous membrane-lined tube running from mouth to
  rumen
• Involved in rumination and eructation
• Differences from monogastric esophagus
• Circular and longitudinal muscles are striated
  muscle along the entire length
• Provides greater strength
• Allows some voluntary control
• Funnel shaped
• Positioned between lungs

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Regions of the ruminant stomach

• of mature
  ___Volume, l___
• __volume__ Cattle
  Sheep
• Rumen 80
  60-100 9-18
• Reticulum 5
• Omasum 5-8
  6-10 1-2
• Abomasum 5-8
  5-8 2
• Full capacity of the reticulorumen is only used
  in animals fed low quality roughages. Only 60 to
  70 of the total capacity is used in animals fed
  high quality roughages.

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The ruminant stomach
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Rumen papillae

• Finger-like structures (10mm x 2 mm) on the rumen
  wall covered with nonsecretory stratified
  epithelial tissue
• Particularly well-developed in ventral portion of
  the rumen
• Function
• Increase absorptive surface for VFAs.
• Growth stimulated by
• Volatile fatty acids
• Irregular growth and damage (Parakeratosis)
  caused by
• Excessive volatile fatty acids (particularly
  Butyrate)

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Omasum

• Lies to right of rumen
• Size
• Large in nonselective grazing species like cattle
• Small in selective grazing species like sheep
• Entrance is the reticulo-omasal orifice
• 1 inch slit in cattle
• Lined with small papillae
• Controls particle of digesta leaving
  reticulorumen
• Round organ containing 100-150 flat parallel
  sheets (laminae) covered with conical papilae
• Because of sheets, omasum has 1/3 of the surface
  area of the stomach in cattle and 10 of the
  stomach surface area in sheep
• Covered with nonsecretory stratified epithelial
  tissue
• Functions
• Filtering large particles
• VFA absorption
• Water absorption

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Regions of the abomasum
Cardiac
Epithelial
Fundic
Pyloric
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The abomasum

• Regions
• Fundic
• Contains gastric glands lined with secretory
  columnar epithelium
• Secrete pepsinogen and hydrochloric acid (Low at
  birth)
• Secrete rennin in young coagulates and digests
  the milk protein, casein
• Pyloric
• Secretes mucus
• Surface
• Arranged in 10 to 17 folds
• Increases surface area
• Prevents stratification of digesta
• Regulates flow

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Motility and digesta flow in the abomasum

• Filled by contractions of the reticulorumen
• Empties by contractions confined to the pyloric
  region
• Outflow controlled by pyloric sphincter
• Flow from the abomasum
• Greatest prior to and during feeding
• Lowest flow occurs immediately after feeding
• Ingesta remains in abomasum for 1 to 2 hours
• As much as 10 backflows into abomasum

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Regions of the small intestine

• Length, ft
• Cattle Sheep
  Digesta pH Functions
• Total 90-150 60-110
• Duodenum 3-4 2-3
  2.7-4 Enzymes
• 
  pH change
• 
  Flow reg.
• Jejunum 60-100 -
  4-7 Enzymes
• 
  Absorption
• Ileum 30-50 -
  7-8 Absorption
• 
  Variable Fermentation
• Rate of pH increase slower than monogastrics
• Better for peptic activity
• May limit pancreatic protease and amylolytic
  activity

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Pancreatic secretion

• Sodium bicarbonate
• Enzymes
• Classes
• Amylase (Low at birth mature levels at 5 6
  months)
• Lipase
• Proteases (Low at birth, mature levels by 8
  weeks)
• Trypsinogen converted to Trypsin
• Chymotrypsinogen converted to Chymotrypsin
• Procarboxypeptidase converted to Carboxypeptidase
• Nucleases
• Activity
• Limited by
• Less pancreatic juice secreted/kg BW than
  monogastrics
• Low digesta pH
• High rate of passage
• Significance
• Limited ability to digest starch in small
  intestine (1 kg)

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Bile

• Composition
• Sodium bicarbonate
• Lipids
• Bile salts (Sodium taurocholate)
• Phospholipids (Phosphotidylcholine)
• Intestinal mucosa
• Enzymes secreted at the brush border (microvilli)
• Disaccharidases
• Lactase (in young)
• Maltase
• Isomaltase
• No sucrase
• Dipeptidases

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Large intestine structure

• Size
• 
  Rumen volumeLI volume
• Roughage selectors
  15-301
• Concentrate selectors
  6-101
• Structure
• Compartments
• Cecum
• Colon
• Rectum
• Properties
• No villi
• No enzymes

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Large intestine functions

• Fermentative digestion
• Bacteria similar to rumen, but no protozoa
• LI digestion may account for as much as 40 of
  carbohydrate digestion
• Only important in conditions that increase the
  amount of fermentative carbohydrate entering the
  LI
• VFAs are efficiently absorbed, but primarily used
  as energy source for mucosa cells
• Ammonia-N absorption
• Allows recycling of N
• Reduced by increased carbohydrate fermentation
• Mineral absorption
• Na, K, Ca, P, Co, Mn, Mg, Cu, Zn, Cl
• Water absorption
• 90 of water entering the LI