Forage Quality &
Forage Quality Testing or the
Forage Quality in Perspective document in Adobe PDF format.
Quality Information via the Forage
Information System (FIS)
Where Should I Send
the Forage Samples for Analyses?
Once you have gone
to the effort of correctly collecting a sample, how can you be sure that
the results you receive from the testing laboratory are accurate? Frequently,
concerns about laboratory testing focus on the methods used in determining
forage quality. However, the focus of concern should be on the accuracy
of results and not the technique of obtaining the results. To help you
determine if the test results are accurate or not, we have outlined below
some questions to ask the laboratory manager.
- Is the lab certified
or does it participate in a check-sample program (also called proficiency
testing program)? The National Forage Testing Association (NFTA) certification
program monitors the performance of a lab against other labs to alert
them of potential problems in their accuracy. The American Association
of Feed Control Officials conduct a check-sample program that insures
consistently and accuracy amoung participating labs. Involvement in
either of these programs indicates that the laboratory is concerned
with the accuracy of its results.
- Does the lab include
duplicate samples or quality control check samples in each group of
samples analyzed? One of the easiest ways for a laboratory to monitor
results is by analyzing replicates of a sample. If the analyses for
replicates are not similar, then there is a problem in the testing procedure.
In addition, the inclusion of standards or check samples (material of
known quality) in each group of samples analyzed can indicate if the
analytical procedure is working correctly or not. Standards or check
samples can also alert the laboratory technician of small changes in
results over time and allow corrective steps to be taken.
- What analytical
methods are used by the laboratory? There is more than one method of
analyses for most plant constituents. Laboratories should be using methods
of analysis which are well validated and approved by the Association
of Official Agricultural Chemists (AOAC).
- Laboratories which
use NIRS can be asked three additional questions that will help determine
if the results are accurate. Like other laboratory methods, NIRS analysis
is sophisticated and should be conducted and monitored by trained personnel.
- How frequently
are the NIRS instrument and the calibration equations monitored? NIRS
instruments should be monitored by running a check sample daily or after
every 25th sample, whichever is more frequent. Calibration equations
should be monitored by conducting laboratory analyses on every 25th
sample. Again, this additional monitoring adds additional costs which
will increase the fee charged for each sample.
- Does the laboratory
do chemical analysis in addition to NIRS? NIRS methods are based on
calibrations derived from chemical methods. NIRS labs which have no
chemical analytical capability have no method within their lab to monitor
the reliability of their calibration equations. It is not impossible
for a NIRS-only lab to have a good monitoring program. But it is much
more difficult since all of the monitoring samples would have to be
sent to another lab for chemical analysis.
- How does the lab
identify and analyze inappropriate samples received for NIRS analysis?
Each NIRS calibration is specific for a particular type of sample. For
example, corn silage is most accurately analyzed with a calibration
equation developed for corn silage and not a calibration equation developed
for alfalfa haylage. How does the lab identify samples that are inappropriate
for the calibration equation and then does it have a protocol for analyzing
Keep in mind that
laboratory monitoring practices increase the cost of the analysis. Asking
these 6 questions will help evaluate a laboratory and is one way to become
more knowledgeable about purchasing analytical services. Laboratories
generally report results of analyses as a single number. This does not
mean that hay which tested at 20% CP is exactly 20.0% CP. Instead, it
means that the hay is 20.0% crude protein plus or minus some variation.
The amount of this variation will differ from lab to lab and from method
to method. A variation of about 3% can be expected between labs for measurements
of crude protein. In other words, a hay sample which tested 20% CP at
one lab would be expected to test anywhere from 19.4 to 20.6% CP at another
lab or at the same lab if the analysis was repeated. Variation is usually
much higher for fiber measurements than for crude protein measurements.