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Microbial Metabolism. Sugars. ADP ATP NADP + NADPH. Biosynthesis. Catabolism. VFA CO 2 CH 4 Heat. Growth Maintenance Transport. Fermentation in the Rumen. Mostly fermentation of sugars from polysaccharides Rumen is an anaerobic habitat

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slide1

Microbial Metabolism

Sugars

ADP

ATP

NADP+

NADPH

Biosynthesis

Catabolism

VFA

CO2

CH4

Heat

Growth

Maintenance

Transport

fermentation in the rumen
Fermentation in the Rumen
  • Mostly fermentation of sugars from polysaccharides
  • Rumen is an anaerobic habitat
  • Disposal of reducing equivalents is a critical feature
  • of anaerobic fermentation
    • Production of lactic acid and ethanol
    • not extensively used in the rumen
    • Production of VFA major pathway
    • Hydrogenases produce hydrogen gas
    • from reduced cofactors
    • Methanogens use hydrogen to produce
  • methane
slide3

Microbial Interactions

Secondary Fermentations

  • Cellulose Fibrobacter Cellulose fragments
  • succinogenes
  • Succinate + Acetate + Formate
          • Selenomonas
          • ruminantium
  • Lactic acid + Propionate + Acetate + Formate + H2
  • Megasphaera
  • elsdenii
  • Propionate + Acetate +H2
fermentation of six carbon sugars glycolysis or embden meyerhof
Fermentation of Six Carbon Sugars (Glycolysis or Embden-Meyerhof)

Accounts for 90% of fermentation in the rumen

Glucose Fructose

Starch Glu-1-P Glu-6-P Fru-6-P Fru-1,6-bisP

Dihydroxyacetone-P

Phospoenolpyruvate Glyceraldehyde-3-P

Pyruvate Glycerol

Predominant pathway for six carbon sugars

(2 ATP + 2 NADH2)/Glucose

6 carbon

Fructose bisphosphate aldolase

3 carbon

an alternate pathway of glucose metabolism entner doudoroff pentose
An Alternate Pathway of Glucose Metabolism(Entner-Doudoroff & Pentose)

Gucose Glu-6-P 6-P-Guconolactone Ribulose-5-P

+ CO2

6-P-gluconate Ribose-5-P

2-Keto-3-deoxy-6-P-gluconate

Pyruvate Glyceraldehyde-3-P

Pyruvate

(1 ATP +1 NADPH)/Glucose

Source of five carbon sugars

NADP NADPH

fermentation of sugars hexose monophosphate pathway
Fermentation of SugarsHexose Monophosphate Pathway

75% of xylan fermented by these pathways

Gucose Glu-6-P 6-P-Guconolactone Ribulose-5-P

+ CO2

Xylulose-5-P

Glyceraldehyde-3-P Ribose-5-P

Acetyl-P

Pyruvate

Phosphoketolase Acetyl CoA

Acetate

Major pathway for five carbon sugars

Source of five carbon sugars for biosynthesis

2 ATP, 2 NADPH, 1 NADH/Glucose

NADP+ NADPH

slide7

Pyruvate production is a central intermediate

in ruminal bacteria and can be converted to

variety of fermentation end products.

The NADH produced during glycolysis must

be re-oxidized so fermentation can continue.

acetic acid
Acetic Acid

1. Pyruvate-formate lyase

Pyruvate Acetyl COA Acetate

Formate

6H CH4 + 2H2O

2. Pyruvate oxidoreductase (Most common pathway)

FD FDH2 (Flavin adenine dinucleotide)

Pyruvate Acetyl COA Acetate

CO2

3 carbon 2 carbon

acetic acid9
Acetic Acid

One pathway for AcetylCoA

AcetylCoA Acetyl-P

ADP

Phosphotransacetylase

Acetate kinase

ATP

Acetate

butyric acid
Butyric Acid

A second pathway for AcetylCoA

FD FDH2 CO2

Pyruvate Acetyl COA Acetaldyhyde

CO2 COA

Acetoacetyl CoA Ethanol

Malonyl COA NADH+H

Acetyl CoA NAD

COA +B-hydroxybutyryl COA

Crotonyl COA

NADH+H

Butyryl COA NAD

Acetate

Butyrate Butyrate-P Acetyl COA

3 carbon

ATP ADP

4 carbon

propionic acid
Propionic Acid

1. Succinate or dicarboxylic acid pathway

Accounts for about 60% of propionate production

ATP

Pyruvate Oxaloacetate Malate

CO2 ADP

Fumarate

NADH+H

Propionly COA Succinate NAD

Propionate

Methylmalonly COA Succinyl COA

Co Vit B12

Pyruvate carboxylase

Uses H

3 carbon

propionic acid12
Propionic Acid

2. Acrylate pathway (mostly by Megasphaera elsdinii)

NADH NAD

Pyruvate Lactic acid

Acrylyl COA

NADH+H

Propionate NAD

Propionyl COA

This pathway becomes more important when

ruminants adjusted to high starch diets

Uses H

methane
Methane
  • CO2 + 4 H2 CH4 + 2H2O
    • The above is the overall reaction
    • There are a number of enzymes and cofactors involved
    • with 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

fermentation of glucose and other sugars
Fermentation of Glucose and Other Sugars

Glucose

Pyruvate CO2

Formate Lactate Oxaloacetate

2H

Acetyl-CoA Malate

Acrylate Fumarate

Acetoacetyl CoA

Succinate

MethaneAcetateButyratePropionate Succinyl CoA

Propionyl CoA Methylmalonyl CoA

Co Vit B12

fermentation balance
Fermentation Balance

Low Acetate (High grain)

Glucose 2 Acetate + 2 CO2 + 8 H

Glucose Butyrate + 2 CO2 + 4 H

Glucose 2 Propionate + 2 [O]

CO2 + 8 H CH4 + 2 H2O

fermentation balance16
Fermentation Balance

High Acetate (High forage)

3 Glucose 6 Acetate + 6 CO2 + 24 H

Glucose Butyrate + 2 CO2 + 4 H

Glucose 2 Propionate + 2 [O]

3 CO2 + 24 H 3 CH4 + 6 H2O

fermentation
Fermentation

Low Acetate

Net: 3 Glucose 2 Acetate + Butyrate + 2 Propionate

+ 3 CO2 + CH4 + 2 H2O

(Acetate:Propionate = 1 Methane:glucose = .33)

High Acetate

Net: 5 Glucose 6 Acetate + Butyrate + 2 Propionate

+ 5 CO2 + 3 CH4 + 6 H2O

(Acetate:Propionate = 3 Methane:Glucose = .60)

energetic efficiency vfa production
Energetic EfficiencyVFA Production

Heat of combustion

kcal/mole kcal/mole of % of of acid glucose fermented glucose

Acetate 209.4 418.8 62.2

Propionate 367.2 734.4 109.1

Butyrate 524.3 524.3 77.9

Glucose 673.0

effect of diet vfa ratios
Effect of DietVFA Ratios
  • Forage:Grain -----Molar ratios-----
    • Acetate Propionate Butyrate
    • 100:0 71.4 16.0 7.9
    • 75:25 68.2 18.1 8.0
    • 50:50 65.3 18.4 10.4
    • 40:60 59.8 25.9 10.2
    • 20:80 53.6 30.6 10.7
branched chain fatty acids
Branched-Chain Fatty Acids

Propionyl CoA + Acetyl CoA Valerate

Valine Isobutyrate + NH3 + CO2

Leucine Isovalerate + NH3 + CO2

Isoleucine 2-methylbutyrate + NH3 + CO2

Fiber digesting bacteria have a requirement for

branched-chain fatty acids.

rumen acidosis
Rumen Acidosis
  • Animals gorge on grain
  • Decrease in rumen pH
    • Megasphaera elsdenii sensitive to acid pH
      • Decreased utilization of lactic acid
    • Streptococcus bovis usually not present in
    • high numbers (107/ml)
      • Grow very fast if sufficient glucose is present
      • Double numbers within 20 min (up to 109/ml)
        • Produce lactic acid
      • Lactobacillus ruminis & L. vitulinus also
      • produce some lactic acid
    • Methanobacter ruminantium in rumen (2 x 108/ml)
      • Sensitive to pH below 6.0
      • Have no capacity to utilize more H+
      • Excess H+accumulates
      • Some formation of ethanol
      • Most is used to produce lactic acid
rumen acidosis22
Rumen Acidosis
  • Increased production of lactic acid
    • Lactic acid poorly absorbed from rumen compared
    • with other VFAs
  • Lactic acid is a relatively strong acid
    • pK: Lactic acid 3.08 A, P, & B 4.75 - 4.81
  • Very low rumen pH
    • Might be pH 5.5 or less
    • Both D and L isomers of lactic acid produced
  • – D is poorly metabolized in the body
    • Results in metabolic acidosis
acidosis
Acidosis
  • Subacute acidosis
    • Decreased fiber digestion
    • Depressed appetite
    • Diarrhea
    • Liver abscess
    • Feedlot bloat
    • Decreased milk fat
  • Acute acidosis
    • Laminitis
    • Death
acidosis24
Acidosis
  • Liver abscess
    • Rumen epithelium not protected by mucous
      • Acid causes inflammation and ulceration (rumenitis)
    • Lactate promotes growth of Fusobacterium necrophorum
      • Fus. necrophorum infects ruminal ulcers
      • If Fus.necrophorum pass from rumen to blood, they
      • colonize in the liver causing abscesses
  • Incidence of liver abscess in feedlot cattle fed high
  • concentrate diets (>60% grain) ranges from 10 to over 50%.
  • Feeding antibiotic Tylosin (10 g/ton of feed) reduces incidence
  • of liver abscess in feedlot cattle.
acidosis25
Acidosis
  • Laminitis (founder)
  • If rumen pH is chronically acidic
    • Epithelium releases metalloproteinases
      • Cause tissue degradation
      • If enter the blood stream causes inflammation
      • of laminae above the hoof
  • Feedlot bloat
  • Starch fermenting bacteria secrete polysaccharides
  • Produces a foam
  • Gas trapped in foam
  • Sudden death
  • If large amounts of starch escape the rumen
    • Overgrowth of Clostridium perfringens in the intestine
    • Produce enterotoxin that might cause death
acidosis26
Acidosis
  • Diarrhea
    • Can be caused by some diseases
    • Often related to the diet in ruminats fed high-grain diets
    • Extensive fermentation in the hind gut
      • Acids produced
        • Absorbed but might cause damage to gut wall
          • Mucin secreted
          • Mucin casts can be observed in feces
        • Retention of water
      • Gas produced
        • Gas bubbles in feces
managing acidosis
Managing Acidosis
  • 1. Allow time for adjustment to diets with grain
  • Gradually increase grain in the diet
    • Program “step up” rations
    • Limit intake until adjusted
  • 2. Feed adequate roughage
    • Effective fiber (eNDF)
  • 3. Manage feed consumption
    • Prevent gorging of high starch feeds
    • “Read bunks”
      • System for knowing when to change
      • amount of feed offered
  • 4. Feed ionophores
adaptation to grain diets two to four weeks
Adaptation to Grain DietsTwo to Four Weeks
  • Allow lactic acid utilizers to increase in numbers
    • Megasphaera elsdenii
      • Rarely present in rumen of hay fed animals
    • Selenomonas ruminantium
    • Propionibacter spp.
    • Not major populations in the rumen
  • Commercial preparations available
  • Maintain protozoa (lost at low pH, <5.5)
    • Ingest starch
    • Engulf bacteria producing lactic acid
    • Use glucose to make polysaccaride
  • Maintain methanogens
    • Use hydrogen
  • Growth of rumen papillae
    • Increased absorption of VFA
action of ionophores transmembrane flux
Action of IonophoresTransmembrane Flux

OutIN

(High NA+, low K+) (High K+, low Na+)

ATP

H+ H+

ADP + Pi

H+ H+

K+ K+

Na+ Na+

H+ H+

M

M

gram negative ionophores excluded
Gram NegativeIonophores Excluded

M

M

Gram - positive Gram-negative

effect of ionophores
Effect of Ionophores

Carbohydrates

Sensitive to Resistant to

ionophore ionophore

Produce more Produce more

acetate & H propionate &

less acetate

CH4

ionophores continued
Ionophores - Continued

Inhibit

Rumminococcus albus Decreased acetate,

Ruminococcus flavefaciens formate and CH4

Butrivibrio fibrisolvens

Increase

Bacteroides succinogenes Increase propionate

Bacteroides ruminicola

Selanomonas ruminantium

Also inhibit

Streptococci Decrease lactate

Lactobacilli production

No effect

Megasphaera Utilize lactate

Selenomonas

ionophores
Ionophores
  • Monensin sodium (Rumensin®)
    • 10 to 30 g per ton of 90% DM feed
    • Feedlot: 27 to 28 g per ton
  • Lasalosid (Bovatec®)
    • 10 to 30 g per ton of 90% DM feed
    • Feedlot: 30 g per ton
  • Laidlomycin propionate (Cattlyst®)
    • 5 to 10 g per ton of 90% DM feed
    • Feedlot: 10 g per ton
effects of rumensin on rumen propionate
Effects of Rumensin on Rumen Propionate

Propionate production

moles/day

Roughage 5.96

Roughage + Rumensin 8.91

Concentrate 6.89

Concentrate + Rumensin 12.15