Rumen CHO Metabolism
AnSci 520
Lance Baumgard
3-2-10
Feed Efficiencies/
Feed to Gain
•
•
•
•
•
Fish (1.2)
Broilers (1.9)
Turkey (2.6)
Swine (2.7)
Beef (> 6.0)
• Why?
CARBOHYDRATES: CHO
• CHO function: ENERGY
– CHO’s are not an essential nutrient
• CHO are made of the elements:
– Carbon
– Hydrogen
– Oxygen
• Hence the acronym (CHO)
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
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 VFA’s, CO2 and CH4
Rumen Digestion and Fermentation
Waste Products
Degradable
CHO
Rumen
microbes
CO2
VFA
Microbial cells
NH3
CH4
Heat
Long-chain
fatty acids
H2S
Microbial Metabolism
Feed
ADP
Catabolism
VFA
CO2
CH4
Heat
ATP
NADP+
NADPH
Bacterial Growth
Maintenance
Transport
Fates of Fermentation Products
Rumen
Fermentation
Products
Hindgut
Organic acids
Absorbed
Absorbed
Recycled
Absorbed
Microbial
protein
Feces
Gas (CO2 &
Methane)
Belch/Bloat
Feces
Mary Beth Hall
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
Energetic Efficiency of VFA
Fermentation and Metabolism
Cellulose
10 Glucose
(6730 kcal)
Starch
VFA
5240 kcal
60A
30P
10B
Absorbed as glucose
(6730 kcal)
ATP
(1946 kcal)
28.9%
ATP
(2888 kcal)
42.9%
Anaerobic vs. Aerobic
Metabolism
• Glucose

• 2-5 ATP
• Acetate
• Propionate
• Butryate
• Lactate
• CO2 and CH4
• H2O
• Heat
• Glucose + O2

• 36-38 ATP
• CO2
• H20
Doesn’t seem like anaerobic is energetically logical??
Dietary Polysaccharides
Bacterial enzymes
Monosacharides (glucose: 6 Carbons)
CH4
H
Glycolysis
CO2
Acetate (2 C)
Butryate (4C)
Pyruvate (3 C)
Propionate (3C)
Fermentation of Glucose and Other Sugars
Glucose
Pyruvate
Formate
2H
Lactate
Acetyl-CoA
Acrylate
Acetoacetyl CoA
CO2
Oxaloacetate
Malate
Fumarate
Succinate
Methane Acetate Butyrate
Propionyl CoA
Propionate Succinyl CoA
Methylmalonyl CoA
– Pyruvate is immediately converted to VFAs
• Acetate production
– Pyruvate oxidoreductase (Most common)
Fd
FDH2
Pyruvate
Coenzyme A
Acetyl CoA
CO2
Acetate
ADP
ATP
– Pyruvate-formate lyase
Coenzyme A
Pyruvate
ADP
Acetyl CoA
Acetate
Formate
CH4 + H2O
6H+
ATP
• Butyrate (60% Butyrate from acetate)
– Condensation
ATP ADP
Pyruvate
CoA
Acetyl CoA
Acetyl CoA
ATP
CO2
ADP
Malonyl CoA
CoA
Acetoacetyl CoA
NADH2
CoA
NAD
B-Hydroxybutyryl CoA
Crotonyl CoA
NADH2
NAD
Butyryl CoA
Acetyl CoA
Acetate
Butyryl P
ADP
ATP
Butyrate
• Propionate
– Succinate or dicarboxylic acid pathway
• 60-90% of propionic acid production
CO2
ATP
ADP
Pyruvate
NADH2 NAD
Oxaloacetate
CO2
Malate
H 2O
Fumarate
Propionyl CoA ADP
NADH2
ATP
NAD
Succinate
Propionate
Methylmalonyl CoA
Succinyl CoA
– Acrylate pathways
• Important on high grain diets
– Accounts of 40% of propionate production
• NADH2 NAD
Pyruvate
Lactate
Acrylyl CoA
NADH2
Propionate
NAD
Propionyl CoA
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
Lyase
Preferred pathway
CO2 + 2 H
3H2
Methane is the predominant hydrogen sink in the rumen
Methanogens use H2 as a source of energy
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
Energy Supply to Ruminants
VFA
70%
Microbial cells
10%
Digestible unfermented feed
20%
Concentration of VFA in the rumen =
50 to 125 uM/ml
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 > propionate > acetate
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
VFA Absorption
Absorption of Ac- (ates)
Rumen
Dissociated:
Ac-
AcHAc
Portal
blood
H+ Metabolism
HCO3H2O
H2CO3
+
CO2
CO2
Metabolism
Free Form:
HAc
HAc
Carbonic
anhydrase
VFA Absorption
Rate of absorption:
Butyrate > Propionate > 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
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
Utilization of Acetate in Metabolism
1. Acetate (As energy)
Acetate
Acetyl CoA
Energy
Krebs cycle
2 carbons
2 CO2
(10 ATP/mole)
2. Acetate (Carbon for synthesis of fatty acids – in AT or MG)
Acetate
Acetyl CoA
Fatty acids
H+NADPH
NADP+
Lipids
Glycerol
Pentose PO4
shunt
CO2
Glucose
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
Utilization of Propionate in Metabolism
Propionate
Propionate
Propionyl CoA
Methylmalonyl CoA
CO2
Glucose
Succinyl CoA
Krebs
cycle
Energy
(18 ATP/mole)
2 CO2
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
Utilization of Butryate in Metabolism
Butyrate (As energy)
Butyrate
Butyrl CoA
B-hydroxybutyrate
Krebs
cycle
Energy
(27 ATP/mole)
Acetyl CoA
2 CO2
Some butyrate also used as a primer for short-chain fatty acids
Glucose is made from propionate
Lactose is made from glucose
Milk yield is determined by the amount of synthesized lactose
Liver
Glucose
(from Propionate)
ATP
Propionic
Feed
Acetic
Butyric
Lactose
Bacteria
Milk Fat
Milk Yield
Utilization of VFA in Metabolism
Summary
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
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
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
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
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
Dietary effects on
Rumen CHO metabolism
Effect of Diet on VFA Ratios
Forage:Grain
100:0
75:25
50:50
40:60
20:80
-----Molar ratios----Acetate Propionate Butyrate
71.4
16.0
7.9
68.2
18.1
8.0
65.3
18.4
10.4
59.8
25.9
10.2
53.6
30.6
10.7
VanSoest
• 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 forage:concentrate 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
• Examples of diet effects on VFA production
– Forage:Concentrate
VFA, Molar%
Acetate
Propionate
Butyrate
Methane, Mcal/d
Forage:Concentrate
60:40 40:60 20:80
66.9
62.9
56.7
21.1
24.9
30.9
12.0
12.2
12.4
3.1
2.6
1.8
– Physical form of forage
VFA, Molar%
Acetate
Propionate
Butyrate
Long
62.5
23.8
10.8
Alfalfa hay
Grind
Coarse Fine
56.8
47.5
27.1
28.5
13.6
23.9
Pelleted
18.2
45.7
32.8
Ruminal Feed Carbohydrate Fermentation Profile
Rate of Fermentation
sugars
Starches and pectin
starches
celluloses
EAT
1
3
5
7
9
11
13
15
Time after Feeding (h)
17
19
21
23
G. Varga
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 > corn
– Harvest and Storage method
• High moisture corn > 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
4
8
16
30
Mary Beth Hall
Pan
Tissue Metabolism
VFA
VFA
GIT tissues
Liver
Body tissues
Use of VFA
Energy
Carbon for synthesis
Long-chain fatty acids
Glucose
Amino acids
Other
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