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Rumen CHO Metabolism

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: C arbon

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Rumen CHO Metabolism

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  1. Rumen CHO Metabolism AnSci 520 Lance Baumgard 3-2-10

  2. Feed Efficiencies/Feed to Gain • Fish (1.2) • Broilers (1.9) • Turkey (2.6) • Swine (2.7) • Beef (> 6.0) • Why?

  3. 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)

  4. 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

  5. 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

  6. Rumen Digestion and Fermentation Waste Products CO2 VFA Degradable Rumen Microbial cells CHO microbes NH3 CH4 Heat Long-chain fatty acids H2S

  7. Microbial Metabolism Feed ADP ATP NADP+ NADPH Biosynthesis Catabolism VFA CO2 CH4 Heat Bacterial Growth Maintenance Transport

  8. Fates of Fermentation Products Fermentation Products Organic acids Microbial protein Gas (CO2 & Methane) Rumen Hindgut Absorbed Absorbed Recycled Absorbed Feces Feces Belch/Bloat Mary Beth Hall

  9. 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

  10. Energetic Efficiency of VFAFermentation and Metabolism Cellulose 10 Glucose VFA ATP (6730 kcal) 5240 kcal (1946 kcal) 60A 28.9% Starch 30P 10B Absorbed as glucose ATP (6730 kcal) (2888 kcal) 42.9%

  11. Glucose  2-5 ATP Acetate Propionate Butryate Lactate CO2 and CH4 H2O Heat Glucose + O2  36-38 ATP CO2 H20 Anaerobic vs. Aerobic Metabolism Doesn’t seem like anaerobic is energetically logical??

  12. Dietary Polysaccharides Bacterial enzymes Monosacharides (glucose: 6 Carbons) CH4 Glycolysis H CO2 Pyruvate (3 C) Propionate (3C) Acetate (2 C) Butryate (4C)

  13. Fermentation of Glucose and Other Sugars Glucose Pyruvate CO2 Formate Lactate Oxaloacetate 2H Acetyl-CoA Malate Acrylate Fumarate Acetoacetyl CoA Succinate MethaneAcetateButyratePropionate Succinyl CoA Propionyl CoA Methylmalonyl CoA

  14. Pyruvate is immediately converted to VFAs

  15. Acetate production • Pyruvate oxidoreductase (Most common) Fd FDH2 Pyruvate Acetyl CoA Acetate Coenzyme A CO2 ADP ATP • Pyruvate-formate lyase Coenzyme A ADP ATP Pyruvate Acetyl CoA Acetate Formate CH4 + H2O 6H+

  16. Butyrate (60% Butyrate from acetate) • Condensation ATP ADP Acetyl CoA CoA Pyruvate Acetyl CoA Acetoacetyl CoA ATP CO2 NADH2 CoA ADP CoA NAD Malonyl CoA B-Hydroxybutyryl CoA Crotonyl CoA NADH2 NAD Butyryl CoA Acetyl CoA Acetate Butyryl P ADP ATP Butyrate

  17. Propionate • Succinate or dicarboxylic acid pathway • 60-90% of propionic acid production CO2 ATP ADP NADH2 NAD Pyruvate Oxaloacetate Malate H2O CO2 Fumarate Propionyl CoA ADP NADH2 ATP NAD Succinate Propionate Methylmalonyl CoA Succinyl CoA

  18. Acrylate pathways • Important on high grain diets • Accounts of 40% of propionate production • NADH2 NAD Pyruvate Lactate Acrylyl CoA NADH2 Propionate NAD Propionyl CoA

  19. 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 • CO2 + 2 H 3H2 • Methane is the predominant hydrogen sink in the rumen • Methanogens use H2 as a source of energy Lyase Preferred pathway

  20. 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

  21. Energy Supply to Ruminants VFA 70% Microbial cells 10% Digestible unfermented feed 20% Concentration of VFA in the rumen = 50 to 125 uM/ml

  22. 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

  23. 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

  24. VFA AbsorptionAbsorption of Ac- (ates) Rumen Ac- Ac-Portal HAc blood H+Metabolism HCO3- H2O H2CO3 + CO2 CO2 Carbonic Metabolismanhydrase HAc HAc Dissociated: Free Form:

  25. 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

  26. 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

  27. Utilization of Acetate in Metabolism 1. Acetate (As energy) Energy Acetate Acetyl CoA Krebs cycle 2 CO2 2 carbons (10 ATP/mole) 2. Acetate (Carbon for synthesis of fatty acids – in AT or MG) Acetate Acetyl CoA Fatty acids Lipids H+NADPH NADP+ Glycerol Pentose PO4 CO2 shunt Glucose

  28. 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

  29. Utilization of Propionate in Metabolism Propionate Propionate Propionyl CoA Methylmalonyl CoA CO2 Succinyl CoA Glucose Krebs cycle 2 CO2 Energy (18 ATP/mole)

  30. 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

  31. Utilization of Butryate in Metabolism Butyrate (As energy) Butyrate Butyrl CoA B-hydroxybutyrate Acetyl CoA Krebs cycle 2 CO2 Energy (27 ATP/mole) Some butyrate also used as a primer for short-chain fatty acids

  32. Liver Glucose is made from propionate Lactose is made from glucose Milk yield is determined by the amount of synthesized lactose Glucose (from Propionate) ATP Propionic Feed Acetic Butyric Lactose Bacteria Milk Fat Milk Yield

  33. Utilization of VFA in MetabolismSummary 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

  34. 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

  35. Comparative Prices of Corn and Alfalfa Hay

  36. Comparative Prices of Corn and Alfalfa Hay *Market prices as of June 2008

  37. 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

  38. Dietary effects on Rumen CHO metabolism

  39. Effect of Diet on VFA Ratios • Forage:Grain -----Molar ratios----- • Acetate Propionate Butyrate • 100:0 71.4 16.0 7.9 • 75:25 68.2 18.1 8.0 • 50:50 65.3 18.4 10.4 • 40:60 59.8 25.9 10.2 • 20:80 53.6 30.6 10.7 VanSoest

  40. 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

  41. Examples of diet effects on VFA production • Forage:Concentrate Forage:Concentrate VFA, Molar%60:4040:6020:80 Acetate 66.9 62.9 56.7 Propionate 21.1 24.9 30.9 Butyrate 12.0 12.2 12.4 Methane, Mcal/d 3.1 2.6 1.8 • Physical form of forage Alfalfa hay Grind VFA, Molar%LongCoarseFinePelleted Acetate 62.5 56.8 47.5 18.2 Propionate 23.8 27.1 28.5 45.7 Butyrate 10.8 13.6 23.9 32.8

  42. sugars Starches and pectin starches celluloses G. Varga

  43. 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

  44. Mary Beth Hall

  45. Tissue MetabolismVFA • VFA GIT tissues Liver • Body tissues • Use of VFA • Energy • Carbon for synthesis • Long-chain fatty acids • Glucose • Amino acids • Other

  46. 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

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