Animal Science 320
Chemical Analysis of Feedstuffs
General Methods
Dry Matter Determination
 Sample is dried in a 100 ° C Oven for 24 hours to remove water.
 % Dry Matter = ending weight / beginning weight x 100
 % Moisture = 100 - % Dry Matter
 Will destroy some nutrients in the sample. Dry at a lower temp (65 ° C) for longer period time (48
hours)
Ash




Muffle furnace at 600 ° C for 2 hours.
Material remaining after oxidation = ash
% Ash = after ashing weight / before ashing weight x 100
% Organic Matter = 100 - % Ash
Protein
 Kjeldahl N
Sample →
Boil in conc. H2SO4→ (NH4)2SO4
→
Acid - Base Titration


Nitrogen Analyzer (LECO)
Sample
→
Pyrrolize sample at high temp.
Add conc. NaOH,
→
distill NH3, and trap
in boric acid
→
Titrate
NH4 borate
Measure N2 w/detector
Most proteins contain 16% Nitrogen
Therefore: measured mg of nitrogen / 100 mg sample x (100 mg protein / 16 mg nitrogen)
Therefore: 100 / 16 = 6.25
% CP = % Nitrogen x 6.25
% CP = measured mg of N / 100 mg sample x 6.25
or
% CP = measured mg of N / 100 mg sample x (100 mg protein / 16 mg nitrogen)
Ether Extract
 Material removed by refluxing ether through a feed sample for 4 hours
 % Ether extract = (Sample wt-residue after ether extract)/Sample wt) x 100%
Crude Fiber
 Sample →

Extract with dilute H2SO4 →
Residue →
followed by dilute NaOH
% CF = (Residue wt - Ash wt)/sample wt x 100%
Nitrogen Free Extract (NFE)
 % NFE = % DM - (%Ash - %CP - %EE - %CF)
Van Soest calculations for ADF and NDF:
 Legumes
Burn at 600oC →
Ash
NEm (Mcal/lb) = 1.1698-0.0111 x NDF
NEg (Mcal/lb) = 0.9095 – 0.0122 x NDF
NE l (Mcal /lb) = 1.0440 – (0.0119 x ADF)
TDN (%) = 4.8980 + (NEl x 89.796)

Grasses
NEm (Mcal/lb) = 1.3875 – 0.0125 x NDF
NEg (Mcal/lb) = 1.2596 – 0.0148 x NDF
NEl (Mcla/lb) = 1.0850 – (0.0124 x ADF)
TDN (%) = 4.8980 + (NEl x 89.796)