Rumen CHO Metabolism

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Rumen CHO Metabolism

• AnSci 520
• Lance Baumgard
• 3-2-10

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Feed Efficiencies/Feed to Gain

• Fish (1.2)
• Broilers (1.9)
• Turkey (2.6)
• Swine (2.7)
• Beef (gt 6.0)
• Why?

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CARBOHYDRATES CHO

• CHO function ENERGY 
• CHOs are not an essential nutrient
• CHO are made of the elements
• Carbon
• Hydrogen
• Oxygen
• Hence the acronym (CHO)

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Rumen CHO Metabolism

• Advantage Can consume worlds most abundant
  organic compound (cellulose)
• Increase digestibility
• Microbes make all of their own amino acids and
  vitamins
• Disadvantage
• Lose energy as heat and CH4
• Loss of dietary glucose

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Rumen CHO metabolism

• Conversion of dietary macromolecules into
  pyruvate
• Starch, cellulose, pectins, and hemicellulose are
  oxidized to pyruvate
• 1) Bacterial enzymes hydrolyze plant
  polysaccharides into monosaccharides
• 2) Monosaccharides are oxidized by glycolysis
  into pyruvate
• 3) Pyruvate is converted into VFAs, CO2 and CH4

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Rumen Digestion and Fermentation
Waste Products
CO2 VFA Degradable
Rumen Microbial cells CHO
microbes NH3 CH4
Heat Long-chain fatty
acids H2S
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Microbial Metabolism
Feed
ADP ATP NADP NADPH
Biosynthesis
Catabolism
VFA CO2 CH4 Heat
Bacterial Growth Maintenance Transport
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Fates of Fermentation Products
Fermentation Products Organic acids Microbial
protein Gas (CO2 Methane)
Rumen
Hindgut
Absorbed
Absorbed
Recycled Absorbed
Feces
Feces
Belch/Bloat
Mary Beth Hall
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Microbial locations

• Adhere tightly to rumen wall
• Associated with feed particles
• Float freely in ruminal liquid
• Microbial Metabolism
• The lack of O2 limits metabolic options
• Presented with surplus reducing equivalents
  (NADH)
• Therefore they reduce all available compounds
• CO2 is reduced to CH4
• Pyruvate is reduced to propionate
• Acetate is reduced to butyrate
• Unsaturated fatty acids are reduced to saturated
  fatty acids

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Energetic Efficiency of VFAFermentation and
Metabolism
Cellulose 10 Glucose VFA ATP (6730 kcal)
5240 kcal (1946 kcal) 60A 28.9 Sta
rch 30P 10B Absorbed as
glucose ATP (6730 kcal) (2888
kcal) 42.9
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Anaerobic vs. Aerobic Metabolism

• Glucose
• ?
• 2-5 ATP
• Acetate
• Propionate
• Butryate
• Lactate
• CO2 and CH4
• H2O
• Heat

• Glucose O2
• ?
• 36-38 ATP
• CO2
• H20

Doesnt seem like anaerobic is energetically
logical??
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Dietary Polysaccharides
Bacterial enzymes
Monosacharides (glucose 6 Carbons)
CH4
Glycolysis
Pyruvate (3 C)
CO2
H
Propionate (3C)
Acetate (2 C)
Butryate (4C)
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Fermentation of Glucose and Other Sugars
Glucose Pyruvate CO2 Formate Lactate O
xaloacetate 2H Acetyl-CoA Malate
Acrylate Fumarate Acetoacetyl
CoA Succinate Methane Acetate Butyrate
Propionate Succinyl CoA Propionyl CoA
Methylmalonyl CoA
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• Pyruvate is immediately converted to VFAs

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• Acetate production
• Pyruvate oxidoreductase (Most common)
• Fd FDH2
• Pyruvate Acetyl CoA
  Acetate
• Coenzyme A CO2
  ADP ATP
• Pyruvate-formate lyase
• Coenzyme A
  ADP ATP
• Pyruvate Acetyl
  CoA Acetate
• 
  Formate
• 
  CH4 H2O
  
• 
  6H

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• Butyrate (60 Butyrate from acetate)
• Condensation
• ATP ADP Acetyl CoA CoA
• Pyruvate Acetyl CoA
  Acetoacetyl CoA
• ATP CO2
  
  NADH2
• CoA ADP
  CoA NAD
• Malonyl CoA
  B-Hydroxybutyryl CoA
• 
  Crotonyl CoA
• 
  NADH2
• 
  NAD
• 
  Butyryl CoA
• 
  Acetyl CoA
• 
  Acetate
• 
  Butyryl P
• 
  ADP
• 
  ATP

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• Propionate
• Succinate or dicarboxylic acid pathway
• 60-90 of propionic acid production
• CO2 ATP ADP NADH2 NAD
• Pyruvate Oxaloacetate
  Malate
• 
  
  H2O
• CO2
  Fumarate
• 
  Propionyl CoA ADP NADH2
• 
  ATP NAD
• 
  Succinate
• 
  Propionate
• 
  Methylmalonyl CoA Succinyl CoA

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• Acrylate pathways
• Important on high grain diets
• Accounts of 40 of propionate production
• NADH2 NAD
• Pyruvate Lactate
  Acrylyl CoA
• 
  
  NADH2
• 
  Propionate
• 
  NAD
• 
  Propionyl CoA

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Methane
CO2 4 H2 CH4 2H2O The above is the overall
reaction. There are a number of enzymes and
cofactors involved in combining CO2 and H2 to
form CH4 Formate 3 H2 CH4 2H2O CO2 2 H
3H2 Methane is the predominant hydrogen
sink in the rumen Methanogens use H2 as a source
of energy
Lyase Preferred pathway
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Volatile Fatty Acids

• Acetate (2 carbons)
• Propionate (3 carbons)
• Butryate (4 carbons)
• All are waste products of microbial metabolism
• But all are utilized by ruminant animal

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Energy Supply to Ruminants
VFA 70 Microbial cells 10 Digestible
unfermented feed 20 Concentration
of VFA in the rumen 50 to 125 uM/ml
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Utilization of fermentation nutrients

• 70-80 of dietary calories and 2/3 of total
  digestible dry matter are absorbed across rumen
  wall
• Rate of diffusion into rumen epithelial cells
  varies with rumen pH and VFA chain length
• ?pH ?absorption
• Butyrate gt propionate gt acetate

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Absorption of VFA
70 of VFA absorbed from rumen-reticulum 60 to
70 of remainder absorbed from omasum Papillae
are important provide surface area Absorption
from rumen is by passive diffusion Concentration
in portal vein less than rumen VFA
concentrations Rumen 50 - 150 mM Portal
blood 1 - 2 mM Peripheral blood 0.5 - 1
mM Absorption increases at lower pH H
Ac- HAc (free form of the acid) Undissociated
acids (free form) diffuse more readily At pH 5.7
to 6.7 both forms are present, however most acids
are dissociated At higher pH, 1 equiv of HCO3
enters the rumen with absorption of 2 equiv of
VFA
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VFA AbsorptionAbsorption of Ac- (ates)
Rumen
Ac- Ac- Portal HAc blood H
Metabolism HCO3- H2O H2CO3
CO2 CO2 Carbonic Metabolism anhydras
e HAc HAc
Dissociated
Free Form
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VFA Absorption
Rate of absorption Butyrate gt Propionate gt
Acetate Absorption greater with increasing
concentrations of acids in the rumen Absorption
increases at lower rumen pH Absorption greater
in grain fed animals Faster fermentation More
VFA produced Lower pH Growth of papillae
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Acetate Utilization

• Absorbed through rumen wall
• Small amt converted to ketone bodies
• Most carried by portal circulation to liver
• 20 converted to acetyl-CoA in hepatocyte
  cytoplasm
• 80 escape oxidation and is exported from liver
• Absorbed by extra-hepatic cells and used for
• Energy via the TCA cycle
• Fatty acid synthesis

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Utilization of Acetate in Metabolism
1. Acetate (As energy) Energy Acetate
Acetyl CoA Krebs cycle 2 CO2 2
carbons (10 ATP/mole) 2. Acetate (Carbon
for synthesis of fatty acids in AT or MG)
Acetate Acetyl CoA Fatty acids Lipids
HNADPH NADP Glycerol Pentose
PO4 CO2 shunt Glucose
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Propionate Utilization

• Absorbed through rumen wall
• 2-5 converted to lactic acid by rumen
  enterocytes
• 95-98 travels to liver
• Converted to succinyl-CoA
• Then converted to glucose

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Utilization of Propionate in Metabolism
Propionate Propionate Propionyl CoA
Methylmalonyl CoA CO2 Succinyl
CoA Glucose Krebs cycle 2
CO2 Energy (18 ATP/mole)
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Utilization of butyrate

• Absorbed through rumen wall
• Used by rumen epithelial cells as an energy
  source
• Largely converted to ketones
• 80 converted into ?-hydroxybutryic acid (?HBA)
• Very low butyrate levels in blood
• ?HBA is oxidized in cardiac and skeletal muscle
  or utilized for fatty acid synthesis in adipose
  tissue (AT) or mammary gland

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Utilization of Butryate in Metabolism
Butyrate (As energy) Butyrate Butyrl
CoA B-hydroxybutyrate Acetyl
CoA Krebs cycle 2
CO2 Energy (27 ATP/mole) Some butyrate
also used as a primer for short-chain fatty acids
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Glucose is made from propionate Lactose is made
from glucose Milk yield is determined by the
amount of synthesized lactose
Glucose (from Propionate)
ATP
Propionic
Feed
Acetic Butyric
Lactose
Bacteria
Milk Fat
Milk Yield
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Utilization of VFA in MetabolismSummary
Acetate Energy Carbon source for fatty
acids Adipose Mammary gland Not used for net
synthesis of glucose Propionate Energy
Precursor of glucose Butyrate Energy Carbon
source for fatty acids - mammary
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Lower Energy Value of Roughage Compared with
Grain

• Less digested
• Lignin limits digestibility of digestible fiber
• - Greater energy lost from fermentation
• CH4 Heat
• - Increased rumination
• Rumen contractions
• Chewing
• - More bulk in digestive tract

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Comparative Prices of Corn and Alfalfa Hay
NEg Mcal/kg /ton DM /Mcal NEg
Corn 1.55 121.75 0.0864
Alfalfa hay 0.68 75.00 0.1213
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Comparative Prices of Corn and Alfalfa Hay
NEg Mcal/kg /ton DM /Mcal NEg
Corn 1.55 185 0.131
Alfalfa hay 0.68 220 0.355
Market prices as of June 2008
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Concentrates decrease pH

• Eating and ruminating times are reduced,
  therefore decreased saliva production
• Rate and extent of acid production is greater
• Forages exert some buffering capacity
• Slower rate of exit

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Dietary effects on Rumen CHO metabolism
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Effect of Diet on VFA Ratios
ForageGrain -----Molar ratios----- Acetate
Propionate Butyrate 1000 71.4 16.0
7.9 7525 68.2 18.1 8.0 5050 65.3
18.4 10.4 4060 59.8 25.9
10.2 2080 53.6 30.6 10.7
VanSoest
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• VFA production
• Usually peaks 4 hours after feeding
• Concentration does not equal production
• Factors that increase propionate, decrease
  acetate and methane
• Factors affecting VFA produced
• Diet forageconcentrate ratio
• Decreased forage and increased concentrate
• Decreased acetate and methane, increased
  propionate
• Dietary buffers
• Increased acetate and methane, decreased
  propionate
• Decreased physical form of diet (grinding,
  pelleting etc)
• Decreased acetate and methane, increased
  propionate
• Ionophores
• Decreased acetate and methane, increased
  propionate
• Unsaturated fatty acids
• Decreased methane, increased propionate

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• Examples of diet effects on VFA production
• ForageConcentrate
• 
  ForageConcentrate
• VFA, Molar 6040 4060 2080
• Acetate 66.9 62.9 56.7
• Propionate 21.1 24.9 30.9
• Butyrate 12.0 12.2 12.4
• Methane, Mcal/d 3.1 2.6 1.8
• Physical form of forage
• 
  Alfalfa hay
• Grind
• VFA, Molar Long Coarse Fine Pelleted
• Acetate 62.5 56.8 47.5 18.2
• Propionate 23.8 27.1 28.5 45.7
• Butyrate 10.8 13.6 23.9 32.8

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sugars
Starches and pectin
starches
celluloses
G. Varga
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Starch

• Dietary Allowance 25-35 of DM as starch
• Varies depending on ruminal starch degradability
• Ruminal Degradability varies with
• Type of grain
• Barley or wheat gt corn
• Harvest and Storage method
• High moisture corn gt dry corn
• For high moisture corn, degradability increases
  with moisture
• Processing
• Degradability increases with fineness of grind
• Starch in steam flake corn is rapidly degraded in
  the rumen
• Starch in rolled corn silage degardes faster than
  if unrolled.

Michel Wattiaux
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Mary Beth Hall
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Tissue MetabolismVFA
VFA GIT tissues Liver Body tissues Use
of VFA Energy Carbon for synthesis Long-chain
fatty acids Glucose Amino acids Other
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Effect of VFA on Endocrine System
Propionate Increases blood glucose Stimulates
release of insulin Butryate Not used for
synthesis of glucose Stimulates release of
insulin Stimulates release of glucagon ?Increases
blood glucose Acetate Not used for synthesis of
glucose Does not stimulate release of
insulin Glucose Stimulates release of insulin