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Ruminant Digestive System
Ruminants
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2.8 billion domesticated ruminants
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Cattle, sheep, deer, elk, bison
Pregastric fermentation
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Ability to chew cud at frequent intervals
distinguishes true ruminant from other foregut
fermenters
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Kangaroo, colobine monkey are not true ruminants
Four compartment stomach
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Reticulum
Rumen
Omasum
Abomasum
Ruminants vary in size and habitat
Classification of Ruminants by
Feeding Preference
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Classes of ruminants
 Concentrate selectors
 Intermediate feeders
 Roughage grazers
Concentrate Selecting Species
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Properties
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Evolved early
Small rumens
Poorly developed omasums
Large livers
Limited ability to digest fiber
Classes
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Fruit and forage selectors
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Very selective feeders
Duikers, sunis
Tree and shrub browsers
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Eat highly lignified plant tissues to extract cell solubles
Deer, giraffes, kudus
Intermediate Feeding Species
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Properties
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Seasonally adaptive
Feeding preference
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Prefer browsing
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Moose, goats, elands
Prefer grazing
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Sheep, impalas
Roughage Grazing Species
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Properties
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Most recently evolved
Larger rumens and longer retention times
Less selective
Digests fermentable cell wall carbohydrates
Classes
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Fresh grass grazers
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Roughage grazers
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Buffalo, cattle, gnus
Hartebeests, topis
Dry region grazers
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Camels, antelope, oryxes
Mouth
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Lips range from short,
relatively immobile in
nonselective grazing species to
very mobile (prehensile) in
selective grazing or
concentrate selecting species
Chew in a lateral (grinding)
motion on one side of mouth at
a time
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Needed to increase surface area
of feed particles
Feed chewed primarily during
rumination in grazing species
Mouth - Teeth
Function:
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Reduce particle size
Anatomy:
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Upper dental pad
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Lower incisors
Premolars
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Molars
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Mouth - Tongue
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Drinking, chewing and forming boluses
Prehension of feed
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Covered with rough, hook-like papillae that assist
in grasping feed
Important in nonselective grazing species
Taste buds
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More numerous than monogastric species
More numerous on nonselective grazing species
Believed that taste is primarily used for food
avoidance by grazing species while concentrate
selecting species select on the basis of smell
Mouth - Saliva
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From at least three paired glands
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Submaxillary, sublingual, parotid (50% of
secretions)
7 L/d sheep
150 L/d cow
Aids in mastication, swallowing, forming bolus
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No digestive enzymes in the saliva of mature
ruminants
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Provides N, P, S and Na for rumen microoganisms
Buffering compounds to maintain rumen pH and
mucin to prevent bloat
Esophagus
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Involved in rumination
Different from monogastric esophagus
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Striated muscle along the entire length
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Provides greater strength
Allows some voluntary control
Funnel shaped
Contains three sphincters active in
rumination and eructation
Ruminant Stomach
Anatomy:
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Reticulum
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Rumen
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Omasum
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Abomasum
Reticulorumen
Although
structurally they
appear as a single
continuous
compartment,
functionally they
are distinctly
different
Reticulum
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Honeycomb lining
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No secretions
Formation of food
bolus
Regurgitation
initiated here
Collects hardware
(nails, wire)
Rumen
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Digestion and
fermentation vat
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Contains anaerobic
microbes (25-50 billion
bacteria/mL fluid)
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Also protozoa, fungi
Produce VFA, protein
Papillae lining
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40-50 gallons
No secretions
Increase surface area
Absorption of VFA
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Passive diffusion
Omasum
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Laminae/manyply lining
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Reduces particle size
Absorption of water
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Muscular folds
No secretions
~60% removed
Absorption of VFAs
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~2/3 of VFAs entering or
10% of total produced
Prevents buffering of the
abomasum
Abomasum, Small Intestine
and Large Intestine
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Similar in structure and function to
monogastric
Differences are subtle but important
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Limited ability to digest starches and
sugars
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Little to none presented except in exceptional
circumstances (high-grain feeding)
Abomasum
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True gastric stomach - four gallons in a cow
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Three regions (cardiac, fundic, and pyloric)
Digestive secretions
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Proteolytic enzymes and HCl
pH decreases
from 6 to 2.5
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Denatures proteins
Kills bacteria
and pathogens
Dissolves minerals
Gastric digestion
Small Intestine
Digesta pH
Duodenum
2.7 - 4
Jejunum
4–7
Ileum
7-8
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Functions
Enzymes
pH change
Flow rate regulation
Enzymes
Absorption
Absorption
Limited fermentation
Rate of pH increase through small intestine is slower than monogastrics
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Better for peptic activity
May limit pancreatic protease and amylolytic activity
Pancreatic Secretions
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Secretion pH is 7.2-7.8
Enzymes
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Amylase
Lipase
Proteases
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Trypsinogen converted to trypsin
Chymotrypsinogen converted to chymotrypsin
Procarboxypeptidase converted to carboxypeptidase
Nucleases
Activity of Pancreatic Enzymes
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Concentration of enzymes in pancreatic juice
comparable to monogastrics
Activity is lower and may be affected by:
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Less juice secreted/kg BW
Low digesta pH
High rate of passage
Limited activity particularly a problem for intestinal
digestion of starch escaping ruminal digestion
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For ruminants fed high grain diets, less than 50% of starch
reaching small intestine is digested
Bile
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Secreted with pancreatic juice in the
common bile duct of sheep
Secreted in the bile duct of cattle
Gastrointestinal Hormones
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Gastrin
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Origin: stomach, abomasum
Stimulus: food in stomach
Function: stimulates HCl & pepsinogen secretion,
increases stomach motility
Secretin
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Origin: duodenum
Stimulus: acid
Function: stimulates pancreatic secretions; slows
stomach motility and acid production
Gastrointestinal Hormones
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Cholecystokinin (CCK)
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Origin: duodenum
Stimulus: fat & protein in duodenum
Function: stimulates bile and pancreatic secretions
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Also regulates appetite and feed intake
Gastric Inhibitory Protein (GIP)
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Origin: duodenum
Stimulus: fats and bile
Function: inhibit stomach motility and secretion of
acid and enzymes
Large Intestine
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Fermentative digestion
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Bacteria similar to rumen, but no protozoa
Digestion in colon may account for as much as:
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Only important in conditions that increase the amount of
fermentative carbohydrate entering the large intestine
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27% of cellulose digestion
40% of hemicellulose digestion
10% of starch digestion
Increased rate of passage of forages
High grain diets
May account for as much as 17% of total VFA absorption
VFAs are efficiently absorbed, but primarily used as energy
source for large intestinal mucosa cells
Large Intestine
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Absorption of ammonia-N
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May account for as much as 30 to 40% of the net
transport of N into body fluid
Absorbed N may be used for:
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Synthesis of nonessential amino acids
Recycling of N to the rumen
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Regulated by:
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Important on low protein diets
Increased by increasing N concentration of diet
Decreased by increasing the amount of carbohydrate
fermented in the large intestine
Mineral absorption
Water absorption
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90% of water entering the LI is absorbed