Transcript CHEMICAL ANALYSIS OF FEEDSTUFFS

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
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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
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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
– Modified distillers grains
– Wet distillers grain
93
50
40
27.9
15.0
12.0
– Affects storage properties of feedstuffs
30
30
30
• 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 NH3, 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