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THE NITROGEN CYCLE

THE NITROGEN CYCLE. ANIMAL AGRICULTURE’S CONTRIBUTION TO N LOADING OF THE ENVIRONMENT. Gaseous emissions % of emissions in the US NH 3 N 2 O NO Total agriculture 80 50 6 Animal agriculture 47-73 25 1

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THE NITROGEN CYCLE

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  1. THE NITROGEN CYCLE

  2. ANIMAL AGRICULTURE’S CONTRIBUTION TO N LOADING OF THE ENVIRONMENT • Gaseous emissions • % of emissions in the US • NH3N2ONO • Total agriculture 80 50 6 • Animal agriculture 47-73 25 1 • Contribution of different species to atmospheric ammonia

  3. Contributions to total N in watersheds

  4. Origin of livestock odor • Odor compound • Large 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 Protein • fermentation Lactic acid • greater at: Butyric acid • Manure pH > 4.5; • High manure moisture; NH3, H2S, mercaptans, branched • High 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

  5. ROLE OF PROTEIN NUTRITION IN N MANAGEMENT OF LIVESTOCK • Proteins are the basic unit of life • Average composition of protein • % • Carbon 53 • Hydrogen 7 • Oxygen 23 • Nitrogen 16 • Possibly sulfur and phosphorus 1

  6. 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.

  7. AMINO ACIDS FOUND IN PROTEINS • 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 • 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

  8. 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 • Phenylalanine • Valine • Tryptophan • Threonine • Isoleucine • Methionine • Histidine • Arginine • Leucine • Lysine • Other amino acids can be synthesized by animal cells and are called ‘nonessential amino acids’

  9. PROTEIN ANALYSIS • In applied nutrition, protein content of feeds is normally determined as crude protein • Crude protein • Calculation • CP% = N% x 6.25

  10. 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

  11. 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.

  12. PROTEIN DIGESTION IN RUMINANTS • Rumen • Total protein • NPN • Undegraded Small intestine • Metabolizable • Degraded protein • Recycled via • saliva • (20% of dietary N) NH3 Microbial • protein • NH3 • Liver • Urea Kidney Excreted

  13. 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 hours • Fish meal 51 • Corn 50 • Cottonseed meal 78 • Soybean meal 89 • Alfalfa 90 • Heat treatments • 100 C for 4 hours • Soybean meal Reduced protein degradation • Tannins in feeds reduce protein degradation • Example: Birdsfoot trefoil

  14. Factors affecting microbial protein production in the rumen • Ruminal NH3-N concentration • Microbial Ruminal NH3-N • protein • (% 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

  15. Protein digestion in the abomasum and small intestine • Similar to nonruminants

  16. 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

  17. 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

  18. 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

  19. FACTORS AFFECTING PROTEIN REQUIREMENTS • Growth • Young, growing animals deposit more protein, but have lower feed intakes than larger animals • Swine, kgCP 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

  20. 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

  21. Maximize the apparent digestibility of N • Feed highly digestible protein sources • Feed processing • Grinding • Pelleting, expanding, or extruding • Enzyme addition (?)

  22. Precision feeding of protein • Avoid feeding protein in excess of requirements • Example (Feeding regimes for swine giving equal performance) • %CP in diets • Grower phase 17.8 17.8 16.2 • Finisher phase 17.1 15.4 13.5 • lb/pig • Manure N 6.3 5.8 4.9 • Gaseous N 2.4 2.1 1.8 • % reduction • Manure N - 9 23 • Gaseous 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

  23. 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 • _______ _______ methionine • g/d • Retained N 26 26 26 • Fecal N 7 7 7 • Urinary N 34 25 17 • Total N excreted 41 32 24 • % reduction - 22 42 • Amino acids currently economically produced • Lysine • Methionine • Threonine • Tryptophan

  24. 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 feedTwo feedsThree feeds • Diet 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 .059 • Reduction - 8.6 15.8 • Typical number of phases • Swine 3-4 • Broilers 4 • Turkeys 6 • Limited by feed storage and handling

  25. 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

  26. 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

  27. 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, % • Forages • Alfalfa 90 • Cool season grasses 90 • Corn silage 60 • Grains and protein supplements • Dry corn 50 • High moisture corn 55-60 • Soybean meal 65 • Expeller soybean meal (Soyplus) 40 • Corn gluten meal 25 • Dry corn gluten feed 70 • Dried distillers grains 50 • Urea 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%

  28. 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

  29. 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%

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