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CHEMICAL ANALYSIS OF FEEDSTUFFS

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CHEMICAL ANALYSIS OF FEEDSTUFFS Powered By Docstoc
					CHEMICAL ANALYSIS OF
    FEEDSTUFFS
    Pages 93-100
FEED NUTRIENTS
        FEED ANALYSIS SYSTEMS
• Needed to rationally group feed nutrients and
  requirements
  – Makes analysis relatively easy and cost-effective
• Feed analysis systems
  – Proximate analysis system (Weende
    system)
     • Developed in 1864 at Weende Experiment
       Station in Germany
  – Detergent analysis system (Van Soest
    system)
     • Developed in 1964 at USDA Beltsville Research
       Center
    PROXIMATE ANALYSIS COMPONENTS

•   Dry matter
•   Ash
•   Crude protein
•   Ether extract
•   Crude fiber
•   Nitrogen-free extract
• Dry matter (DM)
  – Material remaining after a feed is dried in a
    100oC oven for 24 hours
    • DM,% = wt after drying/wt before drying x 100%
    • % moisture = 100 – DM,%
  – Problems with method
    • Errors from losses of volatile components
       – Particularly a problem with fermented feeds
       – Can be avoided by toluene distillation or freeze
         drying
    • Drying at 100oC destroys sample for further
      analysis
       – Can be avoided by freeze drying or drying at 65oC for
         48 hours in preparation for analysis (Still need to run
         a total DM analysis of part of sample)
• Significance of DM
  – Considerable variation in the DM, % of feedstuffs
       •   Corn grain, 88% DM
       •   Alfalfa hay, 90% DM
       •   Alfalfa silage, 45% DM
       •   Alfalfa pasture, 26% DM
       •   Whey, 7%
  – Other nutrients are present within the dry matter
       • Affects expression of concentrations of nutrients in
         feedstuffs
       • Example                             Crude protein, %
                                   DM,% Wet basis DM basis
            – Dried distillers grains       93         27.9          30
            – Modified distillers grains    50         15.0          30
            – Wet distillers grain          40         12.0          30
  – Affects storage properties of feedstuffs
                                    DM,%
      <30            30-60          60-75           75-82           >82
  Putrefaction      Ensiled        Mold &        High moisture   Dry grains
                    forages        heating          grains       and baled
                                                                  forages
• Ash
  – Material remaining after oxidation of a
    sample at 600oC for 2 hours in a muffle
    furnace
    • % Ash = wt after ashing/sample wt x 100%
    • % Organic matter = 100 - % ash
  – Problems
    • No indication of amounts of individual minerals
    • Some minerals (Sulfur, Selenium, Zinc, Iodine
      are lost)
  – Significance
    • May indicate soil contamination or adulteration
      of feedstuff or diet.
• Crude protein (CP)
  – % Crude protein = %N x 6.25
  – %N determination
      • Kjeldahl N
Sample→Boil in conc. H2SO4→(NH4)2SO4→Add conc. NaOH, → Titrate
                                     distill NH 3, and trap NH4 borate
                                     in boric acid
       • N analyzer
Sample→Pyrrolize sample at high temp.→Measure N2 w/detector
   – Factor of 6.25 assumes that most proteins contain
     16% N
   CP,% = measured mg N/100 mg sample x 100 mg protein/16 mg N

         = measured mg N/100 mg/sample x 6.25
• Problems with crude protein procedure
  – Sources of N
     • True protein
        – Chains of amino acids bound by peptide linkages
        – Can meet the protein requirements of either nonruminant or
          ruminant animals
     • Nonprotein nitrogen
        – Forms
            » Free amino acids
            » Nucleic acids
            » Ammonia
            » Urea
            » Biuret
        – Can meet the protein requirements of ruminant animals
            » Urea and biuret commonly added to ruminant diets
        – Can not meet the protein requirements of nonruminant
          animals
  – Says nothing about the amino acid composition of
    the feed source
     • Commonly assume that the concentration of individual
       amino acids is constant within the protein a given feedstuff
     • Can analyze for individual amino acids
– Crude protein says nothing about the digestibility of a
  protein
   • Varies with feedstuff
                         % Crude protein % Protein Digestibility
   Soybean meal                45            90
   Feather meal                80            75
   • Varies with heat damage
      – When overheated, protein will bind to the cell wall
        carbohydrates particularly across lysine
      – Causes
          » Molding of forages
          » Over-heating during processing
          » Over-drying of grains or soybeans
      – Referred to as the Maillard or Browning Reaction
      – Results
                          % Crude protein % Protein Digestibility
   Well-preserved alfalfa hay   18            90
   Heat-damaged alfalfa hay     18            60
• Ether extract (EE)
  – Also called crude fat
  – Material removed by refluxing ether through a
    feed sample for 4 hours
  % Ether extract = (Sample wt-residue after ether extract)/Sample wt x 100%
  – Theoretically represents fat content of the
    feedstuff
      • A high ether extract content should indicate a high
        energy concentration
  – Problem with procedure
      • Ether extract consists of:
          – True lipids
              » Fats and oils
          – Non-nutritional ether soluble components
              » Fat-soluble vitamins
              » Chlorophyll
              » Pigments
              » Volatile oils
              » Waxes
• Crude fiber (CF)
   – Procedure
Sample→Extract with dilute H2SO4 →Residue→Burn at 600oC→Ash
       followed by dilute NaOH

% CF = (Residue wt-Ash wt)/sample wt x 100%
   – Theoretically represents
       • the structural carbohydrates (Cellulose and
         hemicellulose)
          – Limited digestibility in ruminants
          – Poor digestibility in nonruminants
       • Lignin
          – Indigestible by ruminants and nonruminants
   – Problems with procedure
       • Poor recovery of components
                        % recovered
          – Cellulose      90
          – Hemicellulose 50-60
          – Lignin         13-70
• Nitrogen-free extract (NFE)
  – No actual analysis
  – Calculation by difference
    • %NFE = %DM – (%ash+%CP+%EE+%CF)
  – Theoretically represents:
    • Starch
    • Sugars
  – Problems:
    • Contains all of the errors from other analyses
       – Largest error is unrecovered lignin will be placed in
         NFE
WHY IS PROXIMATE ANALYSIS SYSTEM
           STILL USED?
DETERGENT ANALYSIS SYSTEM
• Neutral detergent fiber (NDF)
  – Consists of hemicellulose, cellulose, lignin, cell
    wall bound protein and insoluble ash
  – Significance:
     • Highly related to feed intake
     • DMI, % BW = 120/% NDF
• Acid detergent fiber (ADF)
  – Consists of cellulose, lignin, poorly digested
    protein, and insoluble ash
  – Significance:
     • Highly related to digestibility and energy concentration
     • DDM% = 88.9 – (.779 x %ADF)
     • NEl, Mcal/lb (for legumes) = 1.011 – (0.0113 x %ADF)
  – Combination of DDM (determined from ADF) and
    DMI (determined from NDF) is used to determine
    Relative Feed Value (RFV)
     • RFV=DDM x DMI / 1.29
     • Used for hay marketing
– Nitrogen bound to acid detergent fiber is a measure
  of heat-damaged protein
   • Called ADIN or ADF-CP
– Procedure
Sample→Extract with AD→ADF→Analyze N by
                                   Kjeldahl procedure
ADF-CP, % of total CP= %ADFN x 6.25/%CP x 100%
– Relationship to protein digestibility (called adjusted
  CP)
   • If ADF-CP, % of total CP <14, ADIN is considered digestible
      – Adjusted CP = CP
   • If ADF-CP, % of total CP is >14 and <20
      – Adjusted CP = ((100 – (ADF-CP, % of CP – 7))/100) x CP
   • If ADF-CP, % of total CP is > 20
      – Adjusted CP = CP – ADF-CP, % of CP
• N bound to NDF and ADF used to determine
  rumen degradable, rumen undegradable, and
  indigestible fractions
  Rumen degradable protein = Total CP – (NDFCP, % of CP xTotal CP)
  Rumen undegradable protein = (NDFCP, % of CP xTotal CP) –
                                   (ADFCP, % of CP xTotal CP)
  Indigestible protein = (ADFCP, % of CP xTotal CP)
   OTHER ANALYTICAL PROCEDURES
• Near infrared reflectance spectroscopy
  – Determines the concentrations of protein, amino
    acids, lipids, and carbohydrates based on absorption
    of near infrared light
  – Advantages
     • Rapid
     • Used by most commercial labs
  – Limitations
     • Requires calibration
     • Inability to measure heterogeneous molecules like lignin
     • Inability to measure minerals
• Atomic absorption spectroscopy
  – Used for mineral analysis
  – Procedure
     • Sample ashed and extracted into a solvent
     • Dissolved sample sucked into a flame with a light at a
       specific wavelength going through it
     • Absorption of light directly proportional to absorption of
       light
  – Limitation
     • Expense
• High performance liquid chromatography
  – Used of amino acids and vitamins
  – Procedure
     • Sample dissolved in organic solvent injected into
       column
     • Column differentially separates components
     • Detector measures components as they through the
       column
  – Limitation
     • Expense

				
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