Ruminant Protein Nutrition
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Ruminant Protein Nutrition
More appropriate:Rumen Nitrogen Metabolism
Protein Pathways in the Ruminant
General Information
No proteases in saliva No rumen secretions Microorganisms responsible for
protein digestion in rumen (and reticulum) Bacteria Protozoa
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
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
NPN Utilization
Urea (and most sources of NPN) rapidly degraded to NH3
MO’s don’t care where NH3 comes from
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
Overflow Ammonia
Shortage of energy relative to available NH3
Liver: NH3 Urea Urea recycled or excreted, depending
on animal needs Saliva Rumen wall
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
Protein UtilizationRuminant vs Nonruminant
Similarities and Dissimilarities
Ruminant vs Nonruminant - Similarities
1. At tissue level – Metabolic pathways similar
2. Ruminant tissues can synthesize dispensable AA
3. Cannot synthesize indispensable AA Essential AA must be provided from digestive tract
4. Tissue proteins constantly undergoing turnover
5. AA not stored
6. Constant supply of AA required
Ruminant vs Nonruminant - Dissimilarities
1. Microbial population has profound effect on AA reaching S.I.
a. AA profile at S.I. different from diet Up-grades low quality dietary protein Down-grades high quality dietary protein
b. Enables ruminants to use NPN efficiently Ruminants can be productive without a
source of dietary true protein
c. Animal can survive on low amounts of dietary protein by recycling N (as urea) back to rumen
Ruminant vs Nonruminant - Dissimilarities
1. Microbial population has profound effect on AA reaching S.I. (cont.)
d. Why we say nitrogen metabolism (vs protein metab.) Microbial intervention NH3 formation
e. Disadvantage: more protein can be destroyed in the rumen than is synthesized
Result = Net lossNet loss of proteinAdvantage: can have more protein leaving rumen than is in the diet
Result = Net gainNet gain of protein
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
Net gainNet loss
8.18.8
5.513.8
N entering S.I. vs diet
AA-N entering S.I. (gm/day)
N fed (gm/day)
8% CP20% CPMeasurement
Ruminant vs Nonruminant - Dissimilarities
2. In ruminant nutrition – generally not concerned with AA composition of dietary protein
a. 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
b. Biological value (BV) of microbial protein ~80%
Matching Available Energy with Rates of Protein Degradation
To maximize efficiency of microbial protein synthesis from ammonia, available energy must be present.
Rumen NH3 Following Protein Ingestion
Rumen VFA from Carbohydrate Sources
Matching Protein and
Energy Sources
Protein Supplements for Beef Cows
Type of feed used for beef cows?
Would urea be utilized?
Why is urea included in range pellets?
Range Pellets with NPN
Range Pellets – No NPN
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
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%
Feeding Urea - Dairy
Dairy cows Upper limit ~1% of diet DM Palatability begins to limit intake
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?
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
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
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
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
Energy pathways in the Ruminant
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