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 Composition EAATissueMicrobesCGMSBMBlood meal Met Lys His Phe Trp Thr Leu Ile Val Arg 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 FeedDegradability Urea Casein Barley Soybean meal Alfalfa hay Corn Fish meal

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 NH 3 POOL Dietary Nitrogen Wasted Nitrogen NH 3 UREA LIVER LEVEL TO PROVIDE FOR MAXIMUM MICROBIAL GROWTH MICROBIAL PROTEIN 65% OF PROTEIN 35% OF PROTEIN SMALL INTESTINE AMINO ACIDS PROTEIN 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) Biological Value (BV) Net Protein Value (NPV) Net Protein Value (NPV) Protein Retention Efficiency (PRE) Protein Retention Efficiency (PRE) Protein Efficiency Ratio (PER) Protein Efficiency Ratio (PER)

Biological Value BV = (retained N / absorbed N) x 100 BV = [ N intake – (FN + UN) ] / N intake – FN proposed for maintenance purposes = N intake – [(FN- MFN) +(UN- EUN)] / = N intake – [(FN- MFN) +(UN- EUN)] / N intake – (FN- MFN) N intake – (FN- MFN) proposed for maintenance + growth proposed for maintenance + growth BV =