2.2.1.1 Partial Dry Matter Using Forced-air Drying Ovens
Reference:
Adapted from Goering, H.K. and P.J. Van Soest. 1970. Forage fiber
analyses (apparatus, reagents, procedures, and some
applications). ARS/USDA Handbook No. 379, Superintendent of
Documents, US Government Printing Office, Washington, D.C. 20402
Scope:
This procedure is applicable to all types of forages and is
intended for initial, partial drying of wet samples (less than
85% dry matter, greater than 15% moisture). The procedure has
minimal effect on chemical composition, allowing samples to be
subsequently analyzed for fiber, lignin, or acid detergent
insoluble nitrogen analysis.
Basic Principle:
Moisture is evaporated from sample and partial dry matter is
determined gravimetrically as the residue remaining after oven
drying. Some moisture remains in the sample because drying at
this temperature does not remove all water. Sample should be
equilibrated at room temperature for 2 to 4 hrs before measuring
partial dry matter to minimize the potential change in moisture
that can occur during grinding and storage. Drying at higher
temperatures (greater than 60oC) causes chemical changes in the
sample that affect subsequent fiber, lignin, or acid detergent
insoluble nitrogen analysis.
Equipment:
Forced-air drying oven set at 55o C Top loading electronic
balance, accurate to 0.01 g Pans, sufficient in size to hold 100
to 250 g coarse forage with maximum sample depth of 1.5 inches.
Reagents:
None.
Safety Precautions:
l Use standard precautions when working with electrical equipment
or glassware.
Procedure:
- Dry empty pans at 55oC for 2 hr if non-absorbent (glass,
metal) or 8 hr if absorbent (paper products).
- Weigh empty pans on a top loading balance and record
weight (W1) to nearest 0.01 g.
- Tare empty container to zero and weigh constant volume of
coarse forage into pans recording weight to nearest 0.01
g (W2) filling pans to maximum sample depth of 1.5
inches. Use following approximate weights:
- Low (less than 50%) moisture haylage 70 to 130 g
- High moisture hay crop silage 150 to 250 g
- Corn silage 150 to 250 g
- High moisture corn grain 150 to 250 g
- Dry in forced-air drying oven at 55o C for 16 to 24 hr.
- Air-equilibrate samples for 2 to 4 hr and weigh the
sample and pan recording weight to nearest 0.01 g (W3).
Comments:
- Samples must not be stacked or tightly packed in oven to
prevent free movement of air.
- The oven temperature must not exceed 60oC or heat-damaged
protein will be formed that will affect fiber values.
- This weight approximates a toluene determination moisture
content of silages and other products with significant
levels of volatile compounds.
Calculation: Partial Dry Matter (Partial DM), expressed
as ratio of (w/w) of dry matter to total weight.
Partial DM = W3 - W1 / W2
- Where W1 = tare weight of pan in grams
- W2 = initial weight of sample in grams
- W3 = dry weight of sample and pan in grams
Quality Control:
Laboratory dry matter of partially dried samples should be
between 85 and 95%.
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