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THE NITROGEN CYCLE ANIMAL AGRICULTURE’S CONTRIBUTION TO N LOADING OF THE ENVIRONMENT • Gaseous emissions Total agriculture Animal agriculture % of emissions in the US NH3 N 2O NO 80 50 6 47-73 25 1 • Contribution of different species to atmospheric ammonia • Contributions to total N in watersheds • Origin of livestock odor Odor compound Large intestine Carbohydrates (Starch, cellulose) Protein 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 fermentation Lactic acid greater at: Manure pH > 4.5; High manure moisture; High ambient temperatures) Air Volatile fatty acids and alcohols Protein Butyric acid NH3, H2S, mercaptans, branched chain VFAs (Isobutyric, Isovaleric), Amines (Putrescine, Cadaverine), Phenols (Phenol, p-Cresol), Indoles (indole, Skatole) CH 4 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 53 Hydrogen 7 Oxygen 23 Nitrogen 16 Possibly 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 H2N C OH 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 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’ 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 protein Degraded Recycled via saliva (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 hours 51 50 78 89 90 Fish meal Corn Cottonseed meal Soybean meal Alfalfa • 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 protein (% of Max) Ruminal NH3-N 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 20 kg pig Corn Soybean meal Corn/soybean meal mix Amino acid requirements of pigs (% of protein) Leucine Lysine S-containing AAs Tryptophan 3.8 4.4 2.8 .7 12.5 2.3 3.0 1.1 7.4 6.3 2.6 1.3 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 1-5 5-10 10-20 20-35 35-60 CP reqt. % 27 20 18 16 14 • Sex – Males deposit more protein at a given weight than females 300 kg large frame gaining 1 kg/d Bulls Steers Heifers gm protein/day 807 804 735 • 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 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 – 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 Corn-soybean meal + lysine _______ g/d Retained N Fecal N Urinary N Total N excreted % reduction 26 7 34 41 - _______ 10% CP + lysine threonine tryptophan methionine 26 7 25 32 22 – Amino acids currently economically produced » » » » Lysine Methionine Threonine Tryptophan 26 7 17 24 42 – 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) Diet CP, % N excretion, lb/pig/day Reduction Feeding system Single feed Two feeds Three feeds 17 (55-220 lb) 17 (55-120 lb) 17 (55-110 lb) 15 (120-230 lb)15 (110-165 lb) 12 (165-230 lb) .07 .064 .059 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, % Forages Alfalfa Cool season grasses Corn silage Grains and protein supplements Dry corn High moisture corn Soybean meal Expeller soybean meal (Soyplus) Corn gluten meal Dry corn gluten feed Dried distillers grains Urea 90 90 60 50 55-60 65 40 25 70 50 100 • 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 – Example Yearlings fed for 132 days Diets balance for metabolizable protein and RDP requirements Control diet Phase feeding 13.6 % CP 12.7% CP ___________ __10.1% CP Lb/steer N intake 72.8 59.4 N retained in carcass 7.9 7.9 N excreted 64.9 51.5 % of excreted N volatilized 70.9 60.7 as 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%