ADP

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Microbial Metabolism
Sugars
ADP ATP NADP NADPH
Biosynthesis
Catabolism
VFA CO2 CH4 Heat
Growth Maintenance Transport
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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

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Microbial Interactions Secondary Fermentations
Cellulose Fibrobacter Cellulose
fragments succinogenes Succinate
Acetate Formate Selenomonas
ruminantium Lactic acid
Propionate Acetate Formate
H2 Megasphaera elsdenii Prop
ionate Acetate H2
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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 Glyceraldehy
de-3-P Pyruvate Glycerol Predominant
pathway for six carbon sugars (2 ATP 2
NADH2)/Glucose
6 carbon Fructose bisphosphate
aldolase 3 carbon
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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-glucon
ate Pyruvate Glyceraldehyde-3-P Pyruvate
(1 ATP 1 NADPH)/Glucose Source of five carbon
sugars
NADP NADPH
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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 Acet
yl-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
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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.
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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
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Acetic Acid
One pathway for AcetylCoA
AcetylCoA Acetyl-P ADP
Phosphotransacetylase Acetate kinase ATP
Acetate
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Butyric Acid
A second pathway for AcetylCoA
FD FDH2 CO2
Pyruvate Acetyl COA Acetaldyhyde CO2 COA
Acetoacetyl CoA Ethanol Malonyl COA
NADHH Acetyl CoA NAD COA
B-hydroxybutyryl COA Crotonyl COA
NADHH Butyryl COA NAD Acetate Butyrate
Butyrate-P Acetyl COA
3 carbon
ATP ADP
4 carbon
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Propionic Acid
1. Succinate or dicarboxylic acid
pathway Accounts for about 60 of propionate
production ATP Pyruvate Oxaloacetate Malat
e CO2 ADP Fumarate
NADHH Propionly COA Succinate
NAD Propionate Methylmalonly COA Succinyl
COA Co Vit B12
Pyruvate carboxylase
Uses H
3 carbon
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Propionic Acid
2. Acrylate pathway (mostly by Megasphaera
elsdinii) NADH NAD Pyruvate Lactic
acid Acrylyl COA
NADHH Propionate NAD Propionyl
COA This pathway becomes more important
when ruminants adjusted to high starch diets
Uses H
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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 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
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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
Co Vit B12
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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
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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
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Fermentation
Low Acetate Net 3 Glucose 2 Acetate Butyrate
2 Propionate 3 CO2 CH4 2 H2O
(AcetatePropionate 1 Methaneglucose
.33) High Acetate Net 5 Glucose 6 Acetate
Butyrate 2 Propionate 5 CO2 3 CH4 6
H2O (AcetatePropionate 3
MethaneGlucose .60)
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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
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Effect of DietVFA 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
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Branched-Chain Fatty Acids
Propionyl CoA Acetyl CoA Valerate Valine Is
obutyrate NH3 CO2 Leucine Isovalerate NH3
CO2 Isoleucine 2-methylbutyrate NH3
CO2 Fiber digesting bacteria have a requirement
for branched-chain fatty acids.
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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

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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

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Acidosis
Subacute acidosis Decreased fiber
digestion Depressed appetite Diarrhea Liver
abscess Feedlot bloat Decreased milk fat Acute
acidosis Laminitis Death
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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 (gt60
grain) ranges from 10 to over 50. Feeding
antibiotic Tylosin (10 g/ton of feed) reduces
incidence of liver abscess in feedlot cattle.
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Acidosis
Laminitis (founder) If rumen pH is chronically
acidic Epithelium releases metalloproteinases Caus
e 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
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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
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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

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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,
lt5.5) Ingest starch Engulf bacteria producing
lactic acid Use glucose to make
polysaccaride Maintain methanogens Use
hydrogen Growth of rumen papillae Increased
absorption of VFA
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Action of IonophoresTransmembrane Flux
Out IN (High NA, low K) (High K,
low Na) ATP H H
ADP Pi H H K K
Na Na H H
M
M
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Gram NegativeIonophores Excluded
M
M
Gram - positive Gram-negative
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Effect of Ionophores
Carbohydrates Sensitive to Resistant
to ionophore ionophore Produce
more Produce more acetate H propionate
less acetate CH4
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Ionophores - Continued
Inhibit Rumminococcus albus Decreased
acetate, Ruminococcus flavefaciens formate
and CH4 Butrivibrio fibrisolvens Increase Bacter
oides succinogenes Increase
propionate Bacteroides ruminicola Selanomonas
ruminantium Also inhibit Streptococci
Decrease lactate Lactobacilli
production No effect Megasphaera Utilize
lactate Selenomonas
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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
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Effects of Rumensin on Rumen Propionate
Propionate production
moles/day Roughage 5.96 Roughage
Rumensin 8.91 Concentrate
6.89 Concentrate Rumensin 12.15