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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 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 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 Recycled via saliva (20% of dietary N) Degraded CHOs Small intestine Metabolizable protein VFAs Microbes 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 Fish meal 51 Corn (Grain or DDGS) 50 Cottonseed meal 78 Soybean meal 89 Alfalfa (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 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 – Proteins are digested to amino acids OVERVIEW OF AMINO ACID UTILIZATION AFTER DIGESTION Body Protein Non-protein Derivatives Dietary Protein Cellular Amino Acids Glucose Ammonia TCA cycle CO2 + Energy Urea or Uric acid Fatty acids 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 Thyroxine Amino acid Increase IGF (Liver) Growth hormone Testosterone Insulin Transport Amino acid Muscle DNA synthesis X Synthesis Increase IGF (Muscle) Protein Estrogen Testosterone Degradation • 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 R C O 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 – Detoxifies NH3 H2N C NH2 • Poultry – Synthesis of uric acid; excreted with feces O H N C H N C C O C C N H N H O 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 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 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 degradation (slow) C skeletons H 2S VOCs Fecal N (20-40% of N) Microbial N NH4+ Urine N (60-80% of N) Microbial O urease (rapid) H2N C NH2 + H+ + H2O 2NH4+ Slow aerobic Anerobic NH3 pH (volatile) 2HCO3• In poultry •Urinary N is secreted as uric acid with the feces NO2 N2 FACTORS AFFECTING NH3 LOSS FROM LIVESTOCK HOUSING AND MANURE STORAGE FACILITIES • NH3 volatilization increased by: – Increasing manure pH • Increased by increased HCO3 and NH3 (Gay and Knowlton, 2005) – Increased difference in NH3 concentration between air at manure surface and ambient air Ambient air Manure surface NH3 NH3 NH3 NH3 NH3 NH3 NH3 NH3 NH3 NH3 – 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 Daily scrape and haul from barn Open lot Pile (Cattle/Swine) Pile (Poultry) Compost Deep pit (Poultry) Litter Pit under floor (Swine) Tank above ground top loaded Tank above ground bottom loaded Tank above ground with cover Holding basin Anerobic lagoon w/ no cover Constructed wetlands N loss, % 20-35 40-70 10-40 5-15 20- 50 25-50 25-50 15-30 20-35 5-10 2-30 20-40 70-80 15 N retention, % 65-80 30-60 60-90 85-95 50-80 50-75 50-75 70-85 65-80 90-95 70-98 60-80 15-30 85