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 Utilization Ruminant 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. 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
8% CP
20% CP
Measurement
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 lb, use natural protein (SBM, CSM)
Can’t consume enough for MO’s to meet protein needs
> 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?
Diet 74% corn, 15% fescue hay, urea, molasses, minerals
Weight (lb)
450
675
900
Daily intake (lb) 11
16.5 18
Daily gain (lb/day)
2.5
2.9
2.2
MP required (gm/day)
512
585
506
MP available (gm/day)
430
639
685
% of MP requirement available
89%
109%
135%

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

27. Urea Urea = 281% CP equivalent How can urea have >100% CP?
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 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