Animal Numbers
According to the Guide
for the Care and Use of Laboratory Animals, animal care and use
protocols must contain "Justification of the species and number of
animals requested. Whenever possible, the number of animals requested
should be justified statistically." This is somewhat in contrast to
PHS policy which
states "identification of the species and the approximate number of
animals to be used."
This difference seems to be a significant point of confusion for
people submitting a protocol. Now that this institution is AAALAC
accredited and AAALAC follows the principles of the "Guide", that's
what we follow. The committee often gets the argument, "This is
research.........we don't know how many animals we're going to need
until we do the experiments." Unfortunately, this is not really an
acceptable answer. There are several intentions underlying this
requirement which I will try to outline:
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Scientific
Review: This is a sticky point
for everyone involved. The CHUA does not want to have to
conduct scientific review, nor do they feel particularly
qualified to conduct such a review. Unfortunately, it is
inherently necessary when determining that the appropriate
number of animals are being requested. AAALAC generally
takes the view that if there isn't a clear explanation of
the numbers requested, then there has not been enough
thought or planning put into the project to justify the
animal use. Numbers are really the area that the CHUA
focuses most closely on when doing its "scientific review"
because this is the one area that the committee does feel
fairly comfortable evaluating.
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Statistics: It is always more
desirable if the numbers selected are based on statistical
estimations based on the data to be collected or based on
the numbers required to acheive statistical significance for
similar experiments conducted in the past or published in
the literature. If statistics cannot be applied (or are not
appropriate for the type of experiment), there is a much
stronger need for a clear, logical explanation for why the
numbers in each group were selected.
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Consistency: This is the one
aspect that tends to hold up the most protocols. The number
of animals requested usually appears in 3 different sections
of the protocol; section B (total number), section D(v)
(numbers justification) and section E (procedures). If the
numbers requested are not consistent in these three areas,
it raises a red flag and puts the committee in the position
of not being able to clearly say they understand the
experimental design. If the committee cannot understand the
design, they cannot say the animal use is justified and
therefore cannot approve the protocol.
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Variability: The committee is not
blind to the fact that animal research, by nature, does not
always fit into specific, neat, justifiable groups. There is
not a specific formula that needs to be followed to justify
the numbers, just some thought and good explanation. Any
combination of group sizes or even pooling animal tissues
for in vitro work can be justified using logical
explanations. It is also understood that sometimes things
don't work and more animals are needed do to unforeseen
circumstances. This can easily be handled with an addendum
after the fact. Or, if there is strong scientific reason to
believe that a certain percentage of experiments will fail,
the extra animals can be justified within the original
protocol. It should be realized, however, that a large
percentage of experimental failure obligates the committee
to conduct an even more critical review of the techniques to
ensure that there are not methods available which would
result in a higher success rate with less animal cost.
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