A.  Sampling

1.  Complete ID - everything about the sample

2.  Obtain a representative sample

a.  grain

- sacks             While filling

- bins                or emptying

b.  hay

- drill core is the best

- get a flake from the middle of the bale while feeding (leaves & stems)

- stacks (many grab samples)

c.  Silage

- collect while feeding

- freeze imediately, adding each days samples on top

B.  Proximate Analysis

1.  Most widely used, even though it may be misleading

2.  Proximate analysis includes: Water, Ash, CP, Ether Extract, Crude Fiber, NFE

a.  dry matter - heat sample to a constant wt, at a temperature above the boiling point of water (100 - 105^oC)

Usually 90% in the southeast

- may loose volitiles (especially in silages)  ==> freeze drying is an alternative

b.  Ash (minerals) - burn sample in muffle furnace for 2 hours at 600 ^oC (some are volitile; Cl, Zn, Se, I) ==> wet ashing is alternative

c. Crude Protein (Kjeldahl Process) - digest sample in conc. H₂SO₄ - N is now in form of NH₄SO₄ - neutralize with NaOH, distill, titrate = amount of N.

CP = %N x 6.25 because protein averages 16% N

- analysis does not distinguish one form of N from another

-  Nitrate N is NOT converted to NH₄ salt.

d.  Ether Extract (fat) - will also measure nonnutrient compounds that are soluble in in ether (chlorophyl, pigments, etc.)

e.  Carbohydrates - not determined as such => CHO = CF + NFE

CF = crude fiber - hemicellulose, cellulose, & insoluble lignin.  Is less digestible & less readilly available

NFE = Nitrogen Free Extract - made up of readilly soluble CHO and may contain some hemicellulose and lignin

NFE = 100 - (%water + %ash + %CP + %CF + % EE)

3.  Van Soest Analysis

(page 74 of text figure 2-1)

C.  NIRS - Near Infared Reflectance Spectroscopy

- Computerized (rapid) & low cost

- dry, grind, expose to infared light

- each major organic compund absorbs & reflect light differently

-database is not yet large enough

D.  Vitamin Analysis

 

1.  Not routinely done, usually biological assays

E.  Units of Measure

1.  dry matter basis (d.m.b.) - No water

2.  As-Fed basis - includes the water normally present in the feedstuffs

3.  Air-Dry basis - approximately 90% dry matter (DM)

4.  Examples:

Steer should consume 22 lb of DM/day.  How much feed on an air-dry basis?
Corn	8.8 % CP	89 % DM
High Moisture Corn	7.4 % CP	75 % DM
CP on d.m.b.??	9.9% for both!!
	As Fed --> DM	DM --> As Fed
Nutrient concentration	­	¯
Weight	¯	­

Bottom Line:  Proximate analysis does not provide adequate information regarding palatability, digestibility, toxicity, or nutritional adequacy.

Thus, Further evaluation is needed

 

II.  Feeding Trial  - supplies information about palatability and performance, but doesn’t answer - WHY?

III.  Digestion/Metabolism Trial

A.  Procedure

1.  Run a proximate analysis of the feed

2.  Feed animal known amount

3. Collect feces

4. Run a proximate analysis of the feces

5. Apparent digestibilty (%) = (Nut. intake - Nut. feces / Nut. intake)x100

B.  Methods of fecal collection

1. Metabolism stalls - collect urine and feces separately, animal must be able to lay down & stand freely

2. Feces collection bags - good for males

3. Marker fed with ration at beginning and end of collection period.

IDEAL MARKERS

- should be inert

- contain no element under investigation

- will not diffuse

4 .  Indicator Method

-chromic oxide, lignin, naturally occurring chromagen compounds

Apparent Digestibility =	100-[100 X % indicator in feed X % nutrient in feces
	% indicator in feces     % nutrient in feed

 

5. Adjustment and collection periods (- 3 to 5 days for pigs;- 8 to 10 days for ruminants)