proteins20_20ruminants1 (1).ppt

8/10/2019 proteins20_20ruminants1 (1).ppt

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More appropriate:

Rumen Nitrogen Metabolism


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Protein Pathways in the Ruminant


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General Information

No proteases in saliva No rumen secretions

Microorganisms responsible for protein

digestion in rumen (and reticulum) Bacteria

Protozoa


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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


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Ruminal Protein Degradation

Fermentative digestionenzymes ofmicrobial origin

MO proteases & peptidases cleave peptidebonds and release AA

AA deaminated by microbes, releasing NH3andC-skeleton

MOs use NH3, C-skeleton and energy to

synthesize their own AA Energy primarily from CHOs (starch, cellulose)

Formation of NH3rapid...very few free AA in

rumen


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NPN Utilization

Urea (and most sources of NPN) rapidlydegraded to NH3

MOs dont care where NH3comes from


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Limitations of Microbial Protein Synthesis

Two most likely limitations Energy available

NH3available

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


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Overflow Ammonia

Shortage of energy relative to available NH3

Liver: NH3Urea

Urea recycled or excreted, depending on

animal needs Saliva

Rumen wall


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Protein Leaving Rumen

Microbial protein Escape protein (also called bypass protein)

Enter abomasum & small intestine Digested by proteolytic enzymes similar to

nonruminants

Escape vsBypass protein

Technically not bypass

Reticular groove


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Protein UtilizationRuminant vsNonruminant

Similarities and Dissimilarities


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Ruminant vsNonruminant - Similarities

1. At tissue levelMetabolic pathways similar2. 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


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Ruminant vsNonruminant - Dissimilarities

1. Microbial population has profound effect on AAreaching 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 proteinc. Animal can survive on low amounts of dietary protein

by recycling N (as urea) back to rumen


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1. Microbial population has profound effect on AAreaching S.I. (cont.)

d. Why we say nitrogen metabolism (vsprotein metab.)

Microbial intervention

NH3formation

e. Disadvantage: more protein can be destroyed in therumen than is synthesized

Result = Net lossof protein

Advantage: can have more protein leaving rumenthan is in the diet

Result = Net gainof protein


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Example: More Protein Leaving Rumenthan 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

8.18.85.513.8

N entering S.I. vsdiet

AA-N entering S.I. (gm/day)

N fed (gm/day)

8% CP20% CPMeasurement


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2. In ruminant nutritiongenerally not concernedwith AA composition of dietary protein

a. Type of feed does not affect AA comp. of bacteria andprotozoa leaving rumen

AA comp. of MOs reaching duodenum strikinglysimilar when measured in labs around the world

b. Biological value (BV) of microbial protein ~80%


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Matching Available Energy withRates of Protein Degradation

To maximize efficiency of microbialprotein synthesis from ammonia,available energy must be present.


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Rumen NH3Following Protein Ingestion


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Rumen VFA from Carbohydrate Sources


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Matching Proteinand

Energy Sources


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Protein Supplements for Beef Cows

Type of feed used for beef cows?

Would urea be utilized?

Why is urea included in range pellets?


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Range Pellets

with NPN


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Range PelletsNo NPN


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Feeding Urea - Beef

Feedlot cattle (fed grain or silage diets) Up to 650-750 lb, use natural protein (SBM, CSM)

Cant consume enough for MOs to meet protein needs

>650-700 lb, urea = natural protein as N sourceAbove 0.75% urea in diet DM, start observing

palatability problems (intake)

General recommendation...

dont exceed 1% urea in diet


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Will urea meet the needs of steers at all weights?

Diet 74% corn, 15% fescuehay, 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 requirementavailable

89% 109% 135%


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Feeding Urea - Dairy

Dairy cows Upper limit ~1% of diet DM

Palatability begins to limit intake


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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?


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Urea Toxicity (NH3Toxicity)

Mechanism Rumen [NH3] Rumen pH

As pH , shift from NH4+to NH3

NH3absorbed faster than NH4+

Liver capacity to convert NH3to urea isexceeded

NH3

goes to blood

2 mg NH3/100 ml plasma is toxic


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Signs of toxicityAppear 20-30 min after urea ingestion

Rapid and labored breathing

Tremors Incoordination

Inability to stand & tetany increasinglyapparent


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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 NH3concentration

Takes 6-12 gal.; not practical when several sick


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Prevention Mix feeds well

Dont switch rapidly from natural protein to

ureaAlways have feed available

Dont allow hungry animals access to highlypalatable, high urea diet, feed, or

supplement (including lick tanks)

Dont use urea with low-energy feeds


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Energy pathways in the Ruminant

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