1. Volatile fatty acids

2. Volatile Fatty Acids
Major VFA: acetic acid; propionic acid; butyric acid.
Major VFAs are absorbed and used as primary energy source by ruminants.
The tissue use of VFA is lower than tissue use of the sugars (e.g., glucose).
~10 % of energy consumed is used for fermentation (methane).

3. Cont. Regulation of microbial growth/function Bacteria vs. protozoa
Competition
Environmental pH
Alteration with diet
Alteration with intake

4. Cont. Acetate: mostly from cellulose Propionate: mostly from starch
Important for milk fat synthesis
Propionate: mostly from starch
Important to produce glucose
Butyrate: mostly derived from acetate
Important in ketones usage as an energy source

5. Volatile Fatty Acids (VFA)
Produced from the fermentation of pyruvate
Rumen and hind gut
Types/ratios depends on diet
3 major VFAs
Acetic acid CH3COOH
Propionic acid CH3CH2COOH
Butyric acid CH3CH2CH2COOH

6. Rumen Fermentation Glucose Pyruvate Hemicellulose Starch Sugars
Pectins
Lactic
Acetic
Formic
H2+CO2
Butyric
Propionic
Methane
(CH4)
Cellulose

7. Acetate Pyruvate + Pi + ADP  Acetate + ATP + H2 + CO2
Cellulolytic bacteria
Energy source for rumen epithelium and muscle
Not utilized by liver

8. Acetate utilization
Important as a precursor to de novo fatty acid synthesis
Adipose
Lactating mammary gland
Oxidized via TCA
Activated to acetyl CoA
Used by skeletal muscle, kidneys, and heart for energy
Net gain of 10 ATP per mole of acetate

9. Acetate utilization Dependent upon Energy balance
Generates CO2 and H2O (i.e., ATP) when in low energy balance
Used for fatty acid synthesis when animal is in high energy balance
Arterial concentration
Tissue uptake is directly related to rate of rumen fermentation [blood concentration]

10. Propionate Pyruvate + CoA + 4H+  Propionate + H2O Amylolytic bacteria
Utilized by rumen epithelium
Converted to lactate and pyruvate
Important as a precursor for gluconeogenesis

11. Hepatic propionate metabolism
TCA
Cycle
OAA
Glucose
Succinyl CoA
Coenzyme B12
Methylmalonyl CoA
ADP + Pi
Biotin, Mg ++
ATP
Propionyl CoA
AMP + 2 Pi
ATP
CoA
Propionate

12. Butyrate Pyruvate + CoA  Acetyl-CoA + H2 + CO2
2 Acetyl-CoA + 4H+  Butyrate + H2O + CoA
Metabolized by rumen epithelium to ketone bodies (acetoacetate, -hydroxybutyrate)
Later metabolized in liver
Net ATP production is 25 per mole

13. Ruminal VFA absorption
Rumen
lumen
Rumen
wall
Portal
vein
Acetate 70 50 20
Propionate 20 10 10
Butyrate 10 1 9
Values are relative flux rates

14. Hepatic metabolism of VFA
Peripheral
blood
Rumen
Portal
vein
Liver
Acetate 70 50
Acetate
Propionate 20 10
Glucose
Glucose
CO2
3-hydroxy
Butyrate
(BHB)
3-OH
butyrate
Butyrate 10 1 4

15. Absorption to portal blood
Passively absorbed by rumen epithelium
Rate:
Concentration pH
Chain length
Tissue uptake related to rate of fermentation
Absorbed in undissociated acid form
CH3COOH (acetic acid) vs CH3COO- (acetate)
pK ~4.75

16. Cont. In converting acetate to pyruvate Ionophore feed additives
also CO2; CH4
Ionophore feed additives
Increases propionate
Decreases acetate

17. Normal process Propionate to lactate (normal process)
Causes lowering pH
Lactate to pyruvate
Requires lactate fermenters (altering pH)
this pyruvate is mainly used to synthesize glucose (hepatic tissues)

18. Sudden dietary changes
Propionate to lactate; reduced pH
Lactate needs to be converted to puruvate
Microbes converting lactate grow slow !!!!!
pH continues to drop
Too acidic environment
Lactic acidosis; can be lethal

19. why Sudden changes in diet; too much concentrate
Stress + reduced feed intake
Empty feed bunks
Reduced feed intake; how palatable ?
IMBALANCE BETWEEN MICROBES PRODUCING LACTATE AND MICROBES CONVERTING LACTATE TO PYRUVATE

20. End products
VFAs
CO2
CH4
NH3
Microbes

21. How pH is altered
Diet
Intake
Feeding frequency
Chewing/rumination