Ruminant Protein Nutrition

1. Ruminant Protein Nutrition More appropriate: Rumen Nitrogen Metabolism

3. Protein Pathways in the Ruminant

4. General Information • No proteases in saliva • No rumen secretions • Microorganisms responsible for protein digestion in rumen (and reticulum) • Bacteria • Protozoa

5. Sources of Rumen Nitrogen • Feed • Protein nitrogen • Protein supplements (SBM, CSM, grains, forages, silages... • Nonprotein nitrogen (NPN) • Usually means urea • However, from 5% of N in grains to 50% of N in silage and immature forages can be NPN • Endogenous (recycled) N • Saliva • Rumen wall

6. Ruminal Protein Degradation • Fermentative digestion – enzymes of microbial origin • MO proteases & peptidases cleave peptide bonds and release AA • AA deaminated by microbes, releasing NH3 and C-skeleton • MO’s use NH3, C-skeleton and energy to synthesize their own AA • Energy primarily from CHO’s (starch, cellulose) • Formation of NH3 rapid...very few free AA in rumen

7. NPN Utilization • Urea (and most sources of NPN) rapidly degraded to NH3 • MO’s don’t care where NH3 comes from

8. Limitations of Microbial Protein Synthesis • Two most likely limitations • Energy available • NH3 available • These need to be synchronized • For diets containing urea, may also need • Sulfur (for S-containing AA) • Branched-chain C-skeletons • MO cannot make branched-chain C-chains • These normally not a problem

9. Overflow Ammonia • Shortage of energy relative to available NH3 • Liver: NH3 Urea • Urea recycled or excreted, depending on animal needs • Saliva • Rumen wall

10. Protein Leaving Rumen • Microbial protein • Escape protein (also called “bypass” protein) • Enter abomasum & small intestine • Digested by proteolytic enzymes similar to nonruminants • Escape vs Bypass protein • Technically not “bypass” • Reticular groove

11. Protein UtilizationRuminant vs Nonruminant Similarities and Dissimilarities

12. Ruminant vs Nonruminant - Similarities • At tissue level – Metabolic pathways similar • Ruminant tissues can synthesize dispensable AA • Cannot synthesize indispensable AA • Essential AA must be provided from digestive tract • Tissue proteins constantly undergoing turnover • AA not stored • Constant supply of AA required

13. Ruminant vs Nonruminant - Dissimilarities • Microbial population has profound effect on AA reaching S.I. • AA profile at S.I. different from diet • Up-grades low quality dietary protein • Down-grades high quality dietary protein • Enables ruminants to use NPN efficiently • Ruminants can be productive without a source of dietary true protein • Animal can survive on low amounts of dietary protein by recycling N (as urea) back to rumen

14. Ruminant vs Nonruminant - Dissimilarities • Microbial population has profound effect on AA reaching S.I. (cont.) • Why we say nitrogen metabolism (vs protein metab.) • Microbial intervention • NH3 formation • Disadvantage: more protein can be destroyed in the rumen than is synthesized Result = Net loss of protein Advantage: can have more protein leaving rumen than is in the diet Result = Net gain of protein

15. Measurement 20% CP 8% CP Example: More Protein Leaving Rumen than was in Diet • Weston & Hogan (Australia) first to show this • Fed sheep 2 diets containing 20% and 8% CP • 20%  Lucerne (alfalfa), corn, PNM • 8%  Wheaten hay, corn • Diets supported identical wool growth N fed (gm/day) 13.8 5.5 AA-N entering S.I. (gm/day) 8.8 8.1 N entering S.I. vs diet Net loss Net gain

16. Ruminant vs Nonruminant - Dissimilarities • In ruminant nutrition – generally not concerned with AA composition of dietary protein • Type of feed does not affect AA comp. of bacteria and protozoa leaving rumen • AA comp. of MO’s reaching duodenum strikingly similar when measured in labs around the world • Biological value (BV) of microbial protein ~80%

17. Matching Available Energy with Rates of Protein Degradation To maximize efficiency of microbial protein synthesis from ammonia, available energy must be present.

18. Rumen NH3 Following Protein Ingestion

19. Rumen VFA from Carbohydrate Sources

20. Matching Protein and Energy Sources

21. Protein Supplements for Beef Cows • Type of feed used for beef cows? • Would urea be utilized? • Why is urea included in range pellets?

22. Range Pellets with NPN

23. Range Pellets – No NPN

24. Feeding Urea - Beef • Feedlot cattle (fed grain or silage diets) • Up to 650-750 lb, use natural protein (SBM, CSM) • Can’t consume enough for MO’s to meet protein needs • >650-700 lb, urea = natural protein as N source • Above 0.75% urea in diet DM, start observing palatability problems ( intake) • General recommendation... • don’t exceed 1% urea in diet

25. Will urea meet the needs of steers at all weights?

26. Feeding Urea - Dairy • Dairy cows • Upper limit ~1% of diet DM • Palatability begins to limit intake

27. Urea • Urea = 281% CP equivalent • N = 45% of urea • 45%N x 6.25 = 281% CP • How can urea have >100% CP? • Does this mean anything practical or is it just academic?

28. Urea Toxicity (NH3 Toxicity) • Mechanism • Rumen [NH3]  Rumen pH  • As pH , shift from NH4+ to NH3 • NH3 absorbed faster than NH4+ • Liver capacity to convert NH3 to urea is exceeded • NH3 goes to blood • 2 mg NH3/100 ml plasma is toxic

29. Urea Toxicity (NH3 Toxicity) • Signs of toxicity • Appear 20-30 min after urea ingestion • Rapid and labored breathing • Tremors • Incoordination • Inability to stand & tetany increasingly apparent

30. Urea Toxicity (NH3 Toxicity) • Treatment • Orally dose with 5% acetic acid (~1 gal. for 1,000 lb cow) • Shift equilibrium from NH3 to NH4+ •  rate of absn • Drench with cold water •  rumen temp. which  rate of urea hydrolysis • Dilutes NH3 concentration • Takes 6-12 gal.; not practical when several sick

31. Urea Toxicity (NH3 Toxicity) • Prevention • Mix feeds well • Don’t switch rapidly from natural protein to urea • Always have feed available • Don’t allow hungry animals access to highly palatable, high urea diet, feed, or supplement (including lick tanks) • Don’t use urea with low-energy feeds

32. Energy pathways in the Ruminant