CHEMICAL ANALYSIS OF FEEDSTUFFS Pages 93-100

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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

100 o

C 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 100 o

C destroys sample for further analysis

Can be avoided by freeze drying or drying at 65 o

C 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,%

Dried distillers grains 93

Wet basis DM basis

27.9

30

Modified distillers grains 50 15.0 30

Wet distillers grain 40 12.0 30

Affects storage properties of feedstuffs

Ash

Material remaining after oxidation of a sample at 600 o

C 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. H

2

SO

4

→(NH

4

)

2

SO

4

→Add conc. NaOH, → Titrate distill NH

3

, and trap NH

4 borate in boric acid

N analyzer

Sample→Pyrrolize sample at high temp.→Measure N

2

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

Soybean meal

% Crude protein % Protein Digestibility

45 90

Feather meal

Varies with heat damage

80 75

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

Heat-damaged alfalfa hay

18

18

90

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 H

2

SO followed by dilute NaOH

4

→Residue→Burn at 600 o

C→Ash

% 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

Cellulose

Hemicellulose

Lignin

% recovered

90

50-60

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)

NE l

, 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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