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Protein Metabolism II

Protein Metabolism II. ANS 520. Protein Pathways . Fate of Rumen Ammonia. 1. Bacterial protein synthesis 2. Absorbed from reticulorumen and omasum NH 3 passes from rumen by diffusion into portal blood. (High concentration to low) Form of ammonia dependent on pH of rumen

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Protein Metabolism II

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  1. Protein Metabolism II ANS 520

  2. Protein Pathways

  3. Fate of Rumen Ammonia • 1. Bacterial protein synthesis • 2. Absorbed from reticulorumen and omasum • NH3 passes from rumen by diffusion into portal blood. (High concentration to low) • Form of ammonia dependent on pH of rumen • NH3 + H+ NH4+ • Less absorption at more acid pH • 3. At pH of rumen, no NH3 lost as gas

  4. Fate of Absorbed Ammonia • 1. Transported to liver by portal vein • 2. Converted to urea via urea cycle in liver • NH3 Urea • Urea • cycle • 3. Urea released into blood • 4. If capacity of urea cycle in liver is exceeded • Ammonia toxicity • Over consumption of urea

  5. Fate of Blood Urea • 1. Excreted into urine • 2. Recycled to digestive tract, g N/d • Saliva – Related to concentration of • urea in blood • Sheep: 0.5 to 1.0 • Cattle: 1.0 to 7.6 • Diffusion into GIT • Sheep: 2 to 5 • Cattle: 25 to 40

  6. Urea Diffusion into Rumen Rumen wall Blood urea Urea NH3 Bacterial population • Total N transferred is • greater when high N • diets are fed. • 2. Percentage of diet N • transferred is greater • when low N diet are fed

  7. Urea Diffusion into RumenUpdate Rumen wall Urea transporter Blood urea Urea High [NH3] inhibits NH3 Bacterial population

  8. Adjustments to Low Protein Intake • Kidney • Blood urea Urea • Urine urea • Urea is predominant form of N in urine • Reabsorption of urea by kidney increased • when ruminants fed low N diets • Conserves nitrogen in the body • Greater portion recycled to digestive tract • Sheep fed the same diet tend to • reabsorb more urea than cattle

  9. Nitrogen Recycling - Cattle Marini et al. JAS 2003

  10. Sources of Nitrogen Recycled to GIT • Urea flowing back into digestive tract • Rumen • Saliva • Diffusion from blood • Lower digestive tract (large intestine, colon, cecum) • Diffusion from blood • Endogenous protein secretions into GIT • Mucins • Enzymes • Sloughing of tissue • Turnover of microbial cells in rumen & reticulum

  11. Significance of Recycled Nitrogen • Source of N for microbes when protein consumption • is limited • Wild species • Protein intake during winter is very low • Rumen deficient of nitrogen for microbial activity • Slowly degraded feed proteins • Recycling provides nitrogen for microbial growth • Infrequent feeding of supplemental protein • Programs to reduce supplemental nitrogen • Difficult to make ruminants severely protein deficient

  12. Urea Nitrogen - Cattle Marini et al. JAS 2003

  13. Amino Acid SynthesisAmmonia Fixation • 1. Glutamine synthetase/glutamate synthase • Glutamine synthetase • Glu + NH3 + ATP Gln • Glutmate synthase • -ketoglutarate + glutamine + NADPH2 • 2 Glu • High affinity for NH3 - Concentrates NH3 in • cells – Uses ATP • Because of N recycling this reaction may not • be that important

  14. Amino Acid SynthesisAmmonia Fixation • 2. Glutamic dehydrogenase • -ketoglutarate + NH3 + NADH Glu • Low affinity for NH3 – High concentration of • enzyme in rumen bacteria – Does not use ATP • Probably predominant pathway • 3. Other AA can be synthesized by transamination • reactions with glutamic acid • Estimates of NH3 requirements range from 5 (culture) • to 20 mg/100 ml (in situ digestion)

  15. Amino Acid Composition% Crude Protein or G/100g CP

  16. Amino Acids inUndegraded Feed Proteins His Isl Lys Met Fish meal 3.4 4.2 6.6 3.1 Fish meal residue 2.9 4.9 6.0 2.9

  17. Sources of Amino Acids for Host Animal • 1. Microbial proteins • Quantity determined by: • Fermentability of the feed • Quantity of feed consumed • c) Nitrogen available to microorganisms • 2. Undegraded feed proteins (UIP) • Quantity will vary in relation to: • a) Degradability of feed proteins • b) Quantity of feed proteins consumed

  18. Nutritional Value of Microbial Proteins • 1996 NRC for Beef • Microbial protein 80% digestible in the intestine • UIP 80% digestible in the intestine • 2001 NRC for Dairy and Level 1 CNCPS • Microbial protein 80% digestible in the intestine • Digestibility of RUP (UIP) is variable in Dairy NRC • UIP 80% digestible in Level 1 CNCPS

  19. History of Protein Systems for Ruminants • ISU Metabolizable protein system • Wisconsin system – When urea could be used • Several European systems – Mostly MP systems • 1985 NRC system – Summarized systems & • Proposed a MP system • Used in 1989 Dairy NRC • Cornell CNCPS • 1996 Beef NRC system – Mostly CNCPS system • Used in ISU Brands system • 2001 Dairy NRC system

  20. Metabolizable Protein Model Tissue proteins NH3 Blood urea Urine Amino acid pools Energy NH3 Metabolizable Microbial protein protein Protein Protein from diet Rumen Intestine Feces A B C

  21. Protein Metabolism of RuminantsConcept of Metabolizable Protein • Metabolizable protein (MP) • = Absorbed amino acids or • = Digestible fraction of microbial proteins + digestible fraction of • undegraded feed proteins • Digestible protein (amino acids) available for metabolism • Concept is similar to Metabolizable energy

  22. Protein Metabolism in the Rumen Less Extensively Degraded Protein Feed Rumen Intestine Microbes Digestion Metabolizable protein Undegraded feed

  23. Protein Metabolism in the Rumen Extensively Degraded Protein Feed Rumen Intestine Microbes Digestion NH3 Metabolizable protein Undegraded feed

  24. Metabolizable ProteinSupply to Host Animal • Metabolizable protein (MP): • Microorganisms – Digestible proteins • Undegraded feed proteins – Digestible proteins • Microorganisms • g/d = 0.13 (TDN intake, g/d) (0.8) (0.8) • Microbes 80% true protein that is 80% digested • Feed • g/d = (Feed protein) (Portion undegraded) (0.8) • Feed proteins 80% digested

  25. Absorption of Amino Acids Amino acids and small peptides absorbed by active transport (specific for groups of AA) From intestines Portal blood Transport of amino acids into cells is similar process From blood Cells Active transport, requires energy

  26. Utilization of Absorbed Amino Acids • Via portal vein to liver • Used for synthesis of proteins in liver • Metabolized (deaminated) - Used for • energy – Carbon for glucose • Escape the liver • Carried by blood to body tissues • Used for synthesis of tissue proteins, • milk, fetal growth, wool • Metabolized - Used for energy

  27. Requirements for Absorbed Amino AcidsMetabolizable Protein (MP) • Protein (amino acid) requirements • Maintenance • Growth • Lactation • Pregnancy • Wool

  28. Protein MetabolismConcept of Net Protein • Net protein = protein gained in tissues, • milk, or fetal growth = NP • Metabolizable protein is used with less • than 100% efficiency • Net protein = (MP - Metabolic loss) • As a quantity, net protein is less than • metabolizable protein

  29. Net Protein Required for Production Amino Acids Proteins Milk kg/d = (Milk yield, kg/d) (% protein in milk) Growth g/d = SWG (268 - (29.4 (RE/SWG))) SWG = Shrunk weight gain, kg/d RE = Retained energy, Mcal/d RE obtained from net energy equations.

  30. Protein MetabolismMetabolic Loss • Protein synthesis and metabolism of • amino acids draw from the same pool • Proteins • Amino • acids • Metabolism • Metabolic loss results from continuous • catabolism from amino acid pools • Continuous turnover of tissue proteins adds • to amino acid pools in tissues

  31. Amino Acid (MP) Requirements Maintenance (three fractions) Protein required to support zero gain or production 1. Metabolism Metabolized Urine Milk Amino acids Feces Wool (Synthesis) GIT Scurf (Degradation) Pregnancy Tissue proteins = Endogenous urinary N 2. Proteins lost from body surface (hair, skin, secretions) = Scurf proteins 3. Proteins lost from undigested digestive secretions and fecal bacteria = Metabolic fecal N

  32. Papers for Lab 4/8/10 • doi:10.2527/jas.2009-2218 • “Effects of partial ruminaldefaunation on urea-nitrogenrecycling, nitrogen metabolism, and microbial nitrogen supply in growing lambs fed low or high dietary crude protein concentrations” • doi: 10.2527/jas.2005-614 • “Effects of ractopamine and protein source on growth performance and carcass characteristics of feedlot heifers”

  33. Figure Assignments • Urea-N recycling paper • Table 1-group discussion • Table 2-Jessica A. • Table 3-Kenny B. • Table 4-JJ G. • Figure 1 and 2-Dan K. • Table 5-Kim M. • Table 6-Amir N.

  34. Figure Assignments • Ractopamine paper • Table 1-Jose N. • Table 2-Danielle P. • Table 3-Erin R. • Table 4-Nathan U.

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