THE NITROGEN CYCLE

ANIMAL AGRICULTURE’S CONTRIBUTION TO N LOADING OF THE ENVIRONMENT

• Gaseous emissions % of emissions in the US

NH3 N2O NO

Total agriculture 80 50 6

Animal agriculture 47-73 25 1

• Contribution of different species to atmospheric ammonia

• Contributions to total N in watersheds

• Origin of livestock odor Odor compoundLarge intestine Carbohydrates Protein (Starch, cellulose) Volatile fatty acids (Acetic, Propionic, Butyric acids; may be absorbed or excreted) H2S and mercaptans (Passed as gas) Other amines, phenols, and indoles (Absorbed from LI & excreted in urine)

Manure Carbohydrates(Secondary Volatile fatty acids and alcohols Proteinfermentation Lactic acidgreater at: Butyric acidManure pH > 4.5;High manure moisture; NH3, H2S, mercaptans, branchedHigh ambient temperatures) chain VFAs (Isobutyric, Isovaleric), CH4

Amines (Putrescine, Cadaverine), Phenols (Phenol, p-Cresol), Indoles (indole, Skatole)

Air Emissions increased with increased temperature, moisture, humidity, agitation, dust, pH, wind, surface exposure

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

• Ten amino acids that can’t be synthesized in adequate quantities are called ‘essential amino acids’– Required in diet on nonruminant animals– Essential amino acids

PhenylalanineValineTryptophanThreonineIsoleucineMethionineHistidineArginineLeucineLysine

• Other amino acids can be synthesized by animal cells and are called ‘nonessential amino acids’

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 on 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

Total protein NPN

Undegraded Small intestine Metabolizable Degraded proteinRecycled viasaliva (20% of dietary N) NH3 Microbial protein

NH3

Liver

Urea Kidney Excreted

• 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 50Cottonseed meal 78Soybean meal 89Alfalfa 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

THE PROTEIN REQUIREMENT• Nonruminants

– Not a requirement for protein per se, but really a requirement for the 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 deficiencies

Amino acid requirements of pigs (% of protein)Leucine Lysine S-containing AAs Tryptophan

20 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

DIETARY STRATEGIES TO REDUCE N LOADING OF THE ENVIRONMENT BY NONRUMINANTS

• Reduce feed waste– Animals can be sloppy eaters– Amounts

• 5 – 6% of feed contributing 7.5% of the N in manure– May be as high as 20%

– Strategies• Feed pelleted feeds instead of mash• Do not overfill feeders• Properly position feeders

• Maximize the apparent digestibility of N– Feed highly digestible protein sources– Feed processing

• Grinding• Pelleting, expanding, or extruding

– Enzyme addition (?)

• Precision feeding of protein– Avoid feeding protein in excess of requirements

• Example (Feeding regimes for swine giving equal performance) %CP in dietsGrower phase 17.8 17.8 16.2Finisher phase 17.1 15.4 13.5lb/pigManure N 6.3 5.8 4.9Gaseous N 2.4 2.1 1.8% reductionManure N - 9 23Gaseous N - 12 25

• Advantages– Reduces feed costs– Reduces environmental N load

• Strategies– Feed proteins for optimal gain, not necessarily maximum gain– Minimize safety margins in dietary formulation

– Balance for available amino acids• Strategy

– Utilize high quality protein sources or synthetic amino acids to feed an ‘ideal’ protein

– An ideal protein has all of the essential amino acids in amounts proportional to their requirements relative to lysine

– Potential (200 lb swine) 14% CP 12% CP 10% CP Corn-soybean meal + lysine + lysine threonine tryptophan _______ _______ methionineg/dRetained N 26 26 26Fecal N 7 7 7Urinary N 34 25 17Total N excreted 41 32 24% reduction - 22 42

– Amino acids currently economically produced» Lysine» Methionine» Threonine» Tryptophan

– Separate animals by sex and feeding phase• Separate sex feeding

– Protein requirements» Intact males>Castrated males>Females

• Phase feeding– As animal grows, protein requirement decreases as a

percentage of diet– Potential of phase feeding (Swine) Feeding system Single feed Two feeds Three feedsDiet CP, % 17 (55-220 lb) 17 (55-120 lb) 17 (55-110 lb) 15 (120-230 lb)15 (110-165 lb) 12 (165-230 lb)N excretion, lb/pig/day .07 .064 .059Reduction - 8.6 15.8

– Typical number of phases» Swine 3-4» Broilers 4» Turkeys 6

– Limited by feed storage and handling

• Enhance lean growth (Swine)– Mechanism

• Increases incorporation of amino acids into protein• Reduces the effects of the maintenance requirement

– Strategies• Genetically lean pigs• Feed Ractopamine

– Sold as Paylean for pigs– Used at 18 g/T for 150 to 240 lb (5 weeks)

» Effect decreases after 4 weeks» Can’t be used longer than 90 days

– Mechanism» Shifts energy from fat deposition to muscle growth in

ham, loin, belly and shoulder– Effects

» Increases feed efficiency – 12%» Increases daily gain – 10%» Increases lean gain – 25- 37%» Decreases N excretion by 11 to 34%

– Greatest improvement in genetically lean pigs

STRATEGIES TO REDUCE N EXCRETION BY RUMINANTS

• Increase microbial protein production in the rumen– Maximize feed intake– Supply adequate, but not excess degradable protein– Feed highly digestible grains

• Grain species• Grain variety• Grain processing

– Feed forages with high digestibility

• Balance supply of rumen degradable protein and undegraded protein– Supplemental protein source dependent on forage protein

degradability and energy level• Ruminal degradability of protein

Ruminal degradability of protein, %ForagesAlfalfa 90Cool season grasses 90Corn silage 60Grains and protein supplementsDry corn 50High moisture corn 55-60Soybean meal 65Expeller soybean meal (Soyplus) 40Corn gluten meal 25Dry corn gluten feed 70Dried distillers grains 50Urea 100

• With proper balance of RDP and RUP, dietary N can be reduced by 10 to 15% and N excretion can be reduced by 20%

– Optimal balance of degradable and undegradable protein is dependent on the animals’ body weights (growing-finishing cattle) or stage of lactation (dairy cows)• In young, light-weight cattle or dairy cows in early lactation,

metabolizable protein requirements exceed the amounts of microbial protein produced– Therefore, feed a supplement that is high in undegraded

protein• In feedlot cattle near finish or dairy cows in late

lactation, microbial protein is adequate for metabolizable protein needs– Therefore, no supplemental protein needed if degradable N

needs are met.• Implications

– Phase feed– ExampleYearlings fed for 132 daysDiets balance for metabolizable protein and RDP requirements

Control diet Phase feeding13.6 % CP 12.7% CP

___________ __10.1% CPLb/steerN intake 72.8 59.4N retained in carcass 7.9 7.9N excreted 64.9 51.5% of excreted N volatilized 70.9 60.7as NH3

• Balance diets for essential amino acids by supplementing amino acids that are protected from ruminal degradation– Ruminal degradation of some amino acids are protected by

binding with minerals or poorly degraded proteins– Protected amino acids currently economically viable

• Lysine• Methionine

– Only economically viable for lactating dairy cows– Reduces N excretion by 13 to 20%

• Utilize technologies to enhance incorporation of N into meat or milk– Products

• Implants– Trenbolone acetate (TBA) and/or Estradiol or Zeranol

• Feed additive– Ractopamine (sold for cattle as Optiflex)

• Injection– Bovine somatotropin (sold for daily cattle as Posilac)

– Effects• Increase N incorporation in meat or milk by 15 to 20%