LIVESTOCK’S ROLE INTHE NITROGEN CYCLE IN AGRICULTURAL SYSTEMS

ROLE OF PROTEIN NUTRITION IN N MANAGEMENT OF LIVESTOCK

• Proteins are the basic unit of life• Average composition of protein

%Carbon 53Hydrogen 7Oxygen 23Nitrogen 16Possibly sulfur and phosphorus 1

PROTEIN STRUCTURE• Primary structure

– Chains of amino acids linked by a peptide linkage– Amino acids are organic acids having an amino group on

the alpha-carbon

O

C OH

H2N C H

R– The side chain ( R) is different for each amino acid and

determines the properties of the amino acid and protein– There are 22 amino acids commonly found in proteins in

varying amounts– Order of amino acids in any protein is specific and

associated with the function of that protein.

AMINO ACIDS FOUND IN PROTEINS

• Neutral amino acids (No special group)– Glycine– Alanine– Serine– Valine– Leucine– Isoleucine– Threonine

• Acidic amino acids (Have an extra COOH group)– Aspartic acid– Asparagine– Glutamic acid

• Basic amino acid (Have an extra NH2)– Lysine– Arginine– Histidine– Glutamine

• Sulfur-containing amino acids (Contain S)– Methionine– Cysteine– Cystine

• Aromatic amino acids (Contain a benzene group)– Phenylalanine– Tysosine– Tryptophan

• Imino acids (Heterocyclic amino acids)– Proline– Hydroxyproline

PROTEIN ANALYSIS• In applied nutrition, protein content of feeds is normally

determined as crude protein• Crude protein

– Calculation• CP% = N% x 6.25

• Limitations of CP determination– Nitrogen in feeds may come from true protein or nonprotein

nitrogen sources• True protein

– Only source of protein that can be used by nonruminant (monogastric) animals

• Nonprotein nitrogen (NPN)– NPN may be utilized to meet the protein needs of ruminant

animals– Nonruminants can not utilize NPN

– Crude protein says nothing about the amino acid composition of a feed

• Assume that amino acid composition for any particular feed is constant

– Crude protein says nothing about the digestibility of the protein

PROTEIN DIGESTION IN NONRUMINANTS

• Digestion

Stomach and intestinal enzymes

Protein Amino acids

•Digestion is normally high, but variable Protein digestion, % (swine) Corn 85 Soybean meal 84-87 Wheat 89 Wheat bran 75 Meat and bone meal 84 Poultry byproduct meal 77

•Digestibility may be reduced by excessive heating.

PROTEIN DIGESTION IN RUMINANTS

• Rumen True protein NPN Undegraded Small intestine Metabolizable Degraded protein

Recycled viasaliva (20% of dietary N) NH3 Microbial protein

NH3

Liver

Urea Kidney Excreted

CHOs VFAs

Microbes

• Ruminal degradation of true protein– By ruminal bacteria and protozoa– Not totally desirable

• There is always some loss of NH3

– Reduces efficiency– Increases N excretion

• Valuable to have protein escape ruminal degradation in animals with high protein requirements

– Factors affecting ruminal protein degradation• Protein source

% degraded in 24 hoursFish meal 51Corn (Grain or DDGS) 50Cottonseed meal 78Soybean meal 89Alfalfa (and most other forages) 90

• Heat treatments 100 C for 4 hours Soybean meal Reduced protein degradation• Tannins in feeds reduce protein degradation

– Example: Birdsfoot trefoil

• Factors affecting microbial protein production in the rumen– Ruminal NH3-N concentration

Microbial Ruminal NH3-Nprotein(% of Max) 5 mg%

12% Crude protein in diet, %– Rate of ammonia release

Urea

[NH3] Treshold

Biuret 2 Time after feeding, hours– Energy level of the diet

• Energy and C-skeletons needed by rumen bacteria to produce microbial protein from ruminal NH3

• Protein digestion in the abomasum and small intestine– Similar to nonruminants– Proteins are digested to amino acids

OVERVIEW OF AMINO ACID UTILIZATION AFTER DIGESTION

DietaryProtein

Cellular AminoAcids

Body Protein

Non-proteinDerivatives

TCA cycle

Glucose

CO2 + Energy

Fatty acids

Ammonia

Urea or Uric acid

AMINO ACID METABOLISM • Protein synthesis

– Mechanism• Protein synthesis controlled by DNA in the nucleus of

cells• DNA is divided into subunits of 3 bases specific for each

amino acid• Messenger RNA is produced from DNA• Messenger RNA migrates to ribosomes where it acts as

the template for protein• To be used in protein synthesis, amino acids are bound

to transfer RNA (specific)• Transfer RNA travels along the messenger RNA to place

amino acid in chain• If an given amino acid is not present, synthesis of this

protein stops and no more amino acids will be used

– Hormonal control Growth hormone Amino acid Thyroxine Increase IGF (Liver) Growth hormone Transport Testosterone Insulin Amino acid Muscle

Testosterone

DNA synthesis Synthesis Degradation

Increase IGF (Muscle) Protein

Estrogen

X

• Transamination– Transfer of an amino group from one amino acid to

another carbon chain (called a keto acid) to construct a new amino acid

• Alpha amino acid1 + keto acid2 keto acid1 + alpha amino acid2

– Importance• A method of synthesizing some specific amino

acids from intermediates of carbohydrate metabolism or vis versa

• These amino acids are called ‘nonessential’ because they are not needed in the diet

• Deamination– Releases amino group from excess amino acids– Mechanism NH2 O

R C COOH + O R C COOH + NH3

(C skeleton) H– Uses of C skeleton

• Energy metabolism• Glucose synthesis• New amino acids

– Removal of NH3 O• Mammals

– Synthesis of urea H2N C NH2

– Detoxifies NH3

• Poultry– Synthesis of uric acid; excreted with feces

O

H

C N

H N C

C O

O C C

N N

H H

THE PROTEIN REQUIREMENT• Nonruminants

– Not a requirement for protein per se, but really a requirement for 10 essential amino acids

– Essential amino acids in the diet• For growth of pigs

– Phenylalanine– Valine– Tryptophan– Threonine– Isoleucine– Methionine– Histidine– Arginine – Lysine– Leucine

• Additional amino acids for poultry– Arginine– Glycine

• Cystine can replace ½ of the methionine• Tyrosine can replace 1/3 of the phenyalanine

– Balance of amino acids in a diet is as important as the amounts of individual amino acids

• Amino acids can only be used to the extent of the least abundant amino acid relative to the animal’s requirement

– Remainder of amino acids will be deaminated and N will be excreted as:

» Urea in mammals» Uric acid in poultry» Ammonia in fish

• An excess of one amino acid may cause a deficiency of another amino acid

Excess leucine Deficiencies of valine and isoleucine

• The term “protein quality” refers to the amino acid balance of a protein relative to an animal’s requirement for each of the essential amino acids

– A “high quality protein” called an “ideal protein” has the essential amino acids present in proportions equal to an animal’s requirements.

» It says nothing about the concentration of protein in the diet– A ration with a “high quality protein” may be composed from two

or more feeds if they complement each other’s deficienciesAmino acid requirements of pigs (% of protein)

Leucine Lysine S-containing AAs Tryptophan20 kg pig 3.8 4.4 2.8 .7Corn 12.5 2.3 3.0 1.1Soybean meal 7.4 6.3 2.6 1.3Corn/soybean meal mix 11.5 4.4 2.7 1.2

– An “ideal” protein can be synthesized by adding individual amino acids to a diet

• Ruminant protein requirements– Ruminants have no essential amino acid requirements in their

diets• The rumen microbes can synthesize all of the amino acids

– Ruminants require• Degradable N up to 12% crude protein in the diet dry matter

– To meet the N needs of the rumen bacteria• Undegraded protein above 12% crude protein

FACTORS AFFECTING PROTEIN REQUIREMENTS• Growth

– Young, growing animals deposit more protein, but have lower feed intakes than larger animals

Swine, kg CP reqt. % 1-5 27 5-10 20 10-20 18 20-35 16 35-60 14

• Sex– Males deposit more protein at a given weight than females 300 kg large frame gaining 1 kg/d gm protein/day Bulls 807 Steers 804 Heifers 735

• Production of milk, eggs, or wool

METHODS TO MINIMIZE NITROGEN EXCRETION BY LIVESTOCK

• Nonruminants– Do not overfeed

protein• Separate sexes• Phase feed

– Balance amino acids• Use individual amino

acids

• Ruminants– Do not overfeed

protein• Phase feed

– Properly balance rumen undegraded and degraded proteins

• Undegraded proteins– Young cattle and dairy

cows in early lactation• Degraded proteins

– All other cattle

– Feed high energy diet with degraded proteins

– Growth promotants and BST

MANURE HANDLING AND STORAGE TO MINIMIZE N LOADING OF THE ENVIRONMENT

• Reason to store manure– Preserve and contain manure nutrients until it can be

spread onto the land at a time compatible with climate and cropping system

• Goals– Maintain excreted N in non-volatile organic forms

• Undigested protein• Microbial N• Urea

– Minimize volatilization of NH3

• Minimizes PM2.5

• Minimizes N deposition in terrestial and aquatic ecosystems• Reduces manure odors

– If N is volatilized, it should be in the form of N2

– Prevent losses of N into surface and ground water sources• Provide adequate storage until it can be safely spread

N TRANSFORMATIONS IN LIVESTOCK PRODUCTION AND MANURE STORAGE

FACILITIES

Manure N Anerobic microbial C skeletons H2S degradation (slow) VOCsFecal N(20-40% of N) Microbial N NH4

+ SlowUrine N aerobic Anerobic

(60-80% of N) Microbial NH3 NO2 N2

O urease (rapid) pH (volatile)

H2N C NH2 + H+ + H2O 2NH4+

2HCO3-

• In poultry•Urinary N is secreted as uric acid with the feces

• NH3 volatilization increased by:– Increasing manure pH

• Increased by increased HCO3 and NH3

– Increased difference in NH3 concentration between air at manure surface and ambient air

Ambient air NH3 NH3 NH3 NH3

Manure surface NH3 NH3 NH3 NH3 NH3 NH3

FACTORS AFFECTING NH3 LOSS FROM LIVESTOCK HOUSING AND MANURE

STORAGE FACILITIES

(Gay and Knowlton, 2005)

– Increased surface area– Increased air velocity at surface– Increased ambient temperature

• Increases urease activity

• Increases NH3 mass transfer coefficient

• Increases ventilation from confinement buildings– Decreased ambient temperatures increase NH3 concentrations in

confinement buidings

– Increased moisture

N LOSSES FROM DIFFERENT MANURE HANDLING AND STORAGE SYSTEMS

N loss, % N retention, %Daily scrape and haul from barn 20-35 65-80Open lot 40-70 30-60Pile (Cattle/Swine) 10-40 60-90Pile (Poultry) 5-15 85-95Compost 20- 50 50-80Deep pit (Poultry) 25-50 50-75Litter 25-50 50-75Pit under floor (Swine) 15-30 70-85Tank above ground top loaded 20-35 65-80Tank above ground bottom loaded 5-10 90-95Tank above ground with cover 2-30 70-98Holding basin 20-40 60-80Anerobic lagoon w/ no cover 70-80 15-30Constructed wetlands 15 85