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VOLATILE FATTY ACIDS. Volatile Fatty Acids Major VFA: acetic acid; propionic acid; butyric acid. Major VFAs are absorbed and used as primary energy source.

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Presentation on theme: "VOLATILE FATTY ACIDS. Volatile Fatty Acids Major VFA: acetic acid; propionic acid; butyric acid. Major VFAs are absorbed and used as primary energy source."— Presentation transcript:

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 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 CH 3 COOH Propionic acidCH 3 CH 2 COOH Butyric acidCH 3 CH 2 CH 2 COOH

6 Rumen Fermentation Cellulose Glucose Pyruvate Hemicellulose Starch Sugars Pectins LacticAceticFormicH 2 +CO 2 ButyricPropionic Methane (CH 4 )

7 Acetate Pyruvate + Pi + ADP Acetate + ATP + H 2 + CO 2 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 CO 2 and H 2 O (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 + H 2 O Amylolytic bacteria Utilized by rumen epithelium Converted to lactate and pyruvate Important as a precursor for gluconeogenesis

11 Hepatic propionate metabolism Glucose Propionate Propionyl CoA Methylmalonyl CoA Succinyl CoA OAA TCA Cycle Coenzyme B 12 Biotin, Mg ++ ATP AMP + 2 Pi ATP ADP + Pi CoA

12 Butyrate Pyruvate + CoA Acetyl-CoA + H 2 + CO 2 2 Acetyl-CoA + 4H + Butyrate + H 2 O + 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 Propionate Butyrate Values are relative flux rates

14 Hepatic metabolism of VFA RumenPortal vein Acetate Propionate Butyrate 50 Glucose 3-hydroxy Butyrate (BHB) Liver 3-OH butyrate Acetate Peripheral blood Glucose CO 2 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 CH 3 COOH (acetic acid) vs CH 3 COO - (acetate) pK ~4.75

16 Cont. In converting acetate to pyruvate also CO 2 ; CH 4 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 CO 2 CH 4 NH 3 Microbes

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


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