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 C OH H 2 N 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 NH 2 ) –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 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 via saliva (20% of dietary N) NH 3 Microbial protein NH 3 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 NH 3 –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 NH 3 -N concentration Microbial Ruminal NH 3 -N protein (% of Max) 5 mg% 12% Crude protein in diet, % –Rate of ammonia release Urea [NH 3 ] 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 NH 3

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

OVERVIEW OF AMINO ACID UTILIZATION AFTER DIGESTION Dietary Protein Cellular Amino Acids Body Protein Non-protein Derivatives TCA cycle Glucose CO 2 + 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 acid 1 + keto acid 2 keto acid 1 + alpha amino acid 2 –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 NH 2 O R C COOH + O R C COOH + NH 3 (C skeleton) H –Uses of C skeleton Energy metabolism Glucose synthesis New amino acids –Removal of NH 3 O Mammals –Synthesis of urea H 2 N C NH 2 –Detoxifies NH 3 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

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. % 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 NH 3 Minimizes PM 2.5 Minimizes N deposition in terrestial and aquatic ecosystems Reduces manure odors –If N is volatilized, it should be in the form of N 2 –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 H 2 S degradation (slow) VOCs Fecal N (20-40% of N) Microbial N NH 4 + Slow Urine N aerobic Anerobic (60-80% of N) Microbial NH 3 NO 2 N 2 O urease (rapid) pH (volatile) H 2 N C NH 2 + H + + H 2 O 2NH 4 + 2HCO 3 - In p oultry Urinary N is secreted as uric acid with the feces

NH 3 volatilization increased by: –Increasing manure pH Increased by increased HCO 3 and NH 3 –Increased difference in NH 3 concentration between air at manure surface and ambient air Ambient air NH 3 NH 3 NH 3 NH 3 Manure surface NH 3 NH 3 NH 3 NH 3 NH 3 NH 3 FACTORS AFFECTING NH 3 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 NH 3 mass transfer coefficient Increases ventilation from confinement buildings –Decreased ambient temperatures increase NH 3 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 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 15 85