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by Don
Ball
The
last issue of Cooperative Farming News contained an
article that discussed laboratory analysis of forage. Laboratory
analyses can be extremely useful, but having such analyses run does not
necessarily eliminate all problems associated with assessment of forage
quality. Examples of issues that sometimes arise include the following.
Sampling
Bias
The
biggest source of variation in laboratory analysis results is sampling.
Laboratory personnel report that they receive everything from huge
flakes of hay to small quantities of pulverized feed or forage in a bag
or bottle. The proper way to sample hay is to use a hay probe and take
at least 20 sub-samples from randomly chosen bales from a single lot (a
"lot" is defined as hay from the same field and cut under
uniform conditions within a 48-hour time period).
Failure To
Accept Some
Variation
People
who are in the business of selling hay sometimes complain that a
customer wants hay at a minimum specific level of energy or a maximum
level of fiber and absolutely will not accept anything less. For
example, a customer may have stated he wants no less than 56% total
digestible nutrients (TDN) and would not accept hay containing 55.6% TDN.
While
it is commendable to have high standards, it is important to remember
that there is some variation in hay analysis results. For example,
leaves are much better in quality than stems, so only a small difference
in the amount of leaves versus stems in a sample can impact
substantially on laboratory analysis results. Another example is that
the presence of weeds in hay can likewise affect analysis results.
Finally, there is even a bit of laboratory variation (i.e., there can be
slight differences in results even when a test is run twice on identical
material).
The
point is that laboratory analyses are subject to some variation,
especially due to differences in sampling technique, as discussed
earlier. A laboratory analysis might be best viewed as a reliable
indicator of the approximate forage quality of a lot of hay or other
feed material.
Misunderstandings
About Dry Matter
Some
people apparently are confused about the practical implications of the
percent dry matter in a forage sample, especially with regard to buying
and selling hay. Dry matter is simply the part of a forage or feed other
than water. The nutritive value of forage lies primarily in the energy,
protein, and minerals it contains, because water is inexpensive and
provided to animals separate from forage. Thus, although animal
nutritionists may use "as fed" laboratory analysis values in
calculating animal rations, the forage quality of various lots of hay
should normally be compared on a dry matter basis.
The
dry matter content of hay can be of importance, however. For example, a
ton of hay that is 10% moisture actually contains about 200 more pounds
of dry matter than a ton of hay that is 20% moisture. In addition, high
moisture hay is more likely to contain mold and very low moisture hay of
some forage species may not be eaten readily by animals, either of which
may affect intake and animal performance. |
