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Transcript
VOLATILE FATTY ACIDS 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 goes towards fermentation (methane). Cont. Regulation of microbial growth/function Bacteria vs. protozoa Competition Environmental pH Alteration with diet Alteration with intake Cont. Acetate: mostly from cellulose Important Propionate: mostly from starch Important for milk fat synthesis to produce glucose Butyrate: mostly derived from acetate Important in ketones usage as an energy source Volatile Fatty Acids (VFA) Produced from the fermentation of pyruvate Rumen and hind gut Types/ratios depends on diet 3 major VFAs Acetic acid Propionic acid Butyric acid CH3COOH CH3CH2COOH CH3CH2CH2COOH Rumen Fermentation Starch Hemicellulose Cellulose Sugars Glucose Pectins Pyruvate Lactic Acetic Propionic Butyric Formic H2+CO2 Methane (CH4) Acetate Pyruvate + Pi + ADP Acetate + ATP + H2 + CO2 Cellulolytic bacteria Energy source for rumen epithelium and muscle Not utilized by liver 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 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 Tissue concentration uptake is directly related to rate of rumen fermentation [blood concentration] Propionate Pyruvate + CoA + 4H+ Propionate + H2O Amylolytic bacteria Utilized by rumen epithelium Converted to lactate and pyruvate Important as a precursor for gluconeogenesis Hepatic propionate metabolism Glucose TCA Cycle OAA Succinyl CoA Coenzyme B12 Methylmalonyl CoA ADP + Pi ATP Biotin, Mg ++ Propionyl CoA AMP + 2 Pi ATP Propionate CoA 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 Ruminal VFA absorption Rumen lumen Acetate Rumen wall 70 Portal vein 50 20 Propionate 20 10 10 Butyrate 10 1 9 Values are relative flux rates Hepatic metabolism of VFA Rumen Portal vein Acetate 70 50 Propionate 20 10 Liver Peripheral blood Acetate Glucose Glucose CO2 Butyrate 10 1 4 3-OH butyrate 3-hydroxy Butyrate (BHB) 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 pK ~4.75 (acetic acid) vs CH3COO- (acetate) Cont. In converting acetate to pyruvate also CO2; CH4 Ionophore feed additives Increases propionate Decreases acetate 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) Sudden dietary changes Propionate to lactate; reduced pH Lactate needs to be converted to pyruvate Microbes converting lactate grow slow !!!!! pH continues to drop Too acidic environment Lactic acidosis; can be lethal 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 End products VFAs CO2 CH4 NH3 Microbes How pH is altered Diet Intake Feeding frequency Chewing/rumination