NITROGENOUS COMPOUNDS IN

RUMINANT NUTRITION

Points

Meeting tissue amino acid requirements presents some special challenges Microbial, as well as host N needs, must be

considered Amino acid supply from the rumen

(microbial protein plus undegraded dietary protein; RUP) is variable and hard to predict

Points

Meeting tissue amino acid requirements presents some special challenges Specific amino acid requirements have not

been determined The potential for energy intake to be

limiting is significant

Forms of Nitrogen Needed

Microbes ammonia peptides amino acids

Animal tissues amino acids

assume 10 essential amino acids

Rumen Amino Acid Output

Microbial protein 50-80% of total amino acid composition unaffected by

dietary source limited by energy as well as N

Undegraded protein dietary protein that is not degraded in the

rumen

Rumen Amino Acid Output

Even under optimal feeding conditions, microbial protein alone is not sufficient to meet tissue amino acid requirements in genetically superior ruminants (e.g., high yielding dairy cow)

Animals respond to dietary supplementation with undegradable protein sources

Amino Acid CompositionEAA Tissue Microbe

sCGM SBM Blood meal

MetLysHisPheTrpThrLeuIleValArg

2.78.32.75.31.44.6

10.06.06.73.7

2.710.52.75.21.65.67.55.96.27.0

2.21.92.15.80.52.8

14.93.84.33.8

1.67.22.85.31.63.97.84.94.98.5

1.29.76.26.93.14.1

12.35.07.84.9

EAA = essential amino acids; CGM = corn gluten meal; SBM = soybean meal

Protein Definitions

Crude protein (CP) Total N-containing compounds in a

feed. To calculate the protein percentage,

a feed is first chemically analyzed for N content.

Protein Definitions

Unavailable protein or insoluble crude protein Calculated from N that is bound to the

acid detergent fiber (ADF) fraction of the feed.

Normally, about 10% protein on a DM basis is found in this fraction. Values greater than 10% indicate heat damage.

Protein Definitions

 Available protein Determined by subtracting unavailable

protein from crude protein.

Protein Definitions

Soluble protein The protein fraction composed of both

non-protein nitrogen (NPN) and true protein, which is rapidly degraded in the rumen.

It is normally expressed as a percent of the crude protein.

Protein Definitions

Rumen degradable protein (RDP) Known previously as degradable intake

protein (DIP) Protein or N that is degraded in the

rumen by microorganisms and incorporated into microbial protein or freed as ammonia.

Degradation of Protein

Feed Degradability

UreaCaseinBarleySoybean mealAlfalfa hayCornFish meal

100908060604030

Protein Definitions

Rumen undegradable protein (RUP) Known previously as undegradable intake

protein (UIP) Protein or N that is not degraded in the

rumen by microorganisms but is available to be digested by the ruminant

UREA

NPN

NH3

POOL

Dietary Nitrogen

Wasted Nitrogen

NH3 UREA

LIVER

LEVEL TOPROVIDE FORMAXIMUMMICROBIAL GROWTH

MICROBIAL PROTEIN

65% OF PROTEIN

35% OF PROTEIN

SMALL INTESTINE

AMINO ACIDS

AMINO ACIDSPROTEIN

AMINO ACIDS

PEPTIDES

Reticulo-rumen

RUP

RDP

Metabolizable protein

Satter & Roffler, 1977

Protein Definitions  Non-protein nitrogen (NPN)

All N fed to animals is not necessarily found in proteins. NPN reflects other sources of nitrogen.

An important source of NPN in the ruminant diet is urea. Rumen bacteria can utilize NPN to produce microbial proteins, thus providing amino acids to the cow.

Recommendations for Dairy Cow 18% CP

60% RDP 50% of RDP as soluble CP

40% RUP

Recommendations for Finishing Steer

Diet 85-90% grain; 10-12% CP Corn 40% RDP Barley 80% RDP

Protein evaluation

1. Laboratory methods CP (Kjeldhal) Pepsin digestibility Dye binding test Urease test Chemical score Amino acid Index

Protein evaluation

2. Biological methods Biological Value (BV) Net Protein Value (NPV) Protein Retention Efficiency

(PRE) Protein Efficiency Ratio (PER)

Biological Value

BV = (retained N / absorbed N) x 100BV = [ N intake – (FN + UN) ] / N intake – FN

proposed for maintenance purposes

= N intake – [(FN- MFN) +(UN- EUN)] /

N intake – (FN- MFN)

proposed for maintenance + growth

BV =