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As
discussed in an article in Cooperative Farming News last
month, sensory evaluation of hay (via sight, touch, smell, etc.) can be
useful, but the fact is that accurate laboratory testing of feed and
forage is required to provide the information needed to formulate animal
rations. Furthermore, laboratory testing to assess quality also provides
a highly reliable basis for commercial hay sales.
A
typical laboratory forage analysis includes measurements of dry matter,
crude protein, and fiber (acid detergent fiber and neutral detergent
fiber). Sometimes ash is measured, and when heat-damaged protein is
suspected it may be desirable to measure acid detergent insoluble crude
protein. Some additional results that may be provided on laboratory
reports are also measured, while others such as digestible energy or
protein, net energy, total digestible nutrients, potential intake, etc.,
are calculated or estimated from measured analyses.
Dry
matter - Dry
matter (DM) is the portion (weight) of forage other than water.
Nutrients are typically reported on a DM basis to eliminate the dilution
effect of moisture and to allow more direct comparison of feeds and
easier formulation of diets. To compare prices and nutritive value
between or among lots of forage, they should be adjusted to a DM basis.
Sometimes hay is compared or sold on a 90% DM basis, which closely
resembles the average DM of air dried feeds.
For
hay, excessively low moisture (less than 10%) could indicate brittleness
(and thus low palatability) or excessive leaf loss (which is linked with
lowered forage quality). High moisture (greater than 14 to 18%)
indicates a risk of mold. For silage, excessively low moisture (below
45%) can indicate heat damage, while high moisture (above 70%) is often
associated with poor fermentation and potential intake problems.
Detergent
fiber analysis -
Acid detergent fiber (ADF) and neutral detergent fiber (NDF) are
commonly used as standard forage testing techniques for fiber analysis.
NDF approximates the total cell wall constituents including
hemi-cellulose, whereas ADF primarily represents cellulose and lignin.
ADF is often used to calculate digestibility, and NDF is used to predict
intake potential. As fiber increases, forage quality declines.
Protein
-
Protein is a key nutrient that must be considered both in amount and
type for various animal diets. It is commonly measured as crude protein
(CP), which is 6.25 times the nitrogen content of forage. Crude protein
is used rather than just "protein" because rumen microbes can
convert non-protein nitrogen in microbial protein, which can then be
used by the animal. However, this value should be used with some care,
as it is not applicable to non-ruminants or when high levels of nitrate
are present in the forage.
High-performing
animals, especially milking dairy cows, need larger amounts of protein
to be absorbed from the intestines than rumen microbes produce.
Therefore, they need a certain amount of "rumen bypass
protein" (or RUP) in the ration. Recently, calibrations have been
developed that allow RUP in forages to be estimated using near infrared
reflectance spectroscopy, which is a quick and easy measurement
technique.
Digestible
energy estimates -
Energy is typically the most limiting nutritional factor on livestock
farms and thus is usually of particular interest and importance.
However, energy values can be determined directly only by feeding
trials. Therefore, laboratory reports provide calculated values of
energy. The most common has been to measure a single fiber fraction
(usually ADF) and use it to calculate an estimated digestibility, total
digestible nutrients (TDN) or net energy for lactation (NE1). |
