Ed, it is not a good idea to take in dead ferrets, especially 50-60 of
them, and I wouldn't recommend ANYONE donate them.  There are a variety of
reasons for this recommendation and any one would negate the study you are
attempting to do, rendering your results absolutely useless.
 
1) Your facilities probably do not come up to state or federal requirements
for the handling, storage and deposition of dead animals.  You risk your
own ferrets, or even to other people who might visit your place because of
the possibility of diesease introduction.  There are state-by-state and
federal requirements for the storage of dead animals, their deposition,
handling and disposal you would need to meet.
 
2) How are you going to process the ferret carcasses to obtain the skulls?
If not properly processed, bones can become a health hazard, or worse, the
processing can actually change the dental morphology.  In tooth ageing
studies, even a fraction of a millimeter can be significant.  Certain types
of processing can cause shrinkage, spalling, cracking, pitting, and even
exfoliation of the enamel.  The method to process these remains must be
carefully controlled or the data is absolutely worthless.
 
3) Did you read my earlier post?  The best ageing range you can ever hope
for is a year (plus or minus a year).  That MEANS that you STILL have a 3
year range.  3 YEARS.  In other words, the best you would be able to say
is "that ferret could be 4, 5 or 6 years old." Most people can GUESS that
accurately.  Most shelter operators are better than that, and those who are
not could be with a little practice.  You simply cannot do better without
more scientific methods, which means tooth extraction from living ferrets.
There is simply NO non-invasive technique that can be improved by your
skull study.  60 ferrets or 6000, you will STILL have a 3 year range.
 
4) While ferret dentition studies are lacking, they have been extensively
done on American mink.  I can provide more than a dozen good references
which have found that what I am telling you about ferret teeth is true
about mink teeth (and some have good photos and drawings).  If these
criteria cannot be set for mink, and mink teeth are so similar to ferret
teeth that only a few teeth can be told apart by experts, how do you
propose to find them for ferrets?
 
5) Ageing techniques which utilize human-interpreted visual discrimination
criteria are extremely error-prone.  I have made over 5 MILLION
measurements on animal bones in the last few years, including perhaps
700,000 measurements on teeth alone.  I use metal templates so I always
measure the exact same point on a bone or tooth, $700 electronic calipers
which measure to 0.01 millimeter and can send the information directly to
a lap top computer to reduce transcription error, and a $400 statistical
program to evaluate my results.  In the last 3 years, I have measured the
skulls and teeth of 320 American mink, 52 black-footed ferrets, 19 European
polecats, 13 steppe polecats, 6 European mink, 58 feral ferrets, 11 whole
domesticated ferrets, and 64 neutered domesticated ferrets.  With ALL that
data, even *I* cannot set up photos which could be used to accurately
determine age using visual discrimination criteria.
 
6) You have a severe methodological problem in the setting up of your
ageing criteria.  Because of individual variation, there is a lot of
difference between ferrets.  You can get around this by measuring the
degree of that variation, but to do so, you need a large number of
individuals.  How many?  Most scientist would think 20 individuals are
too small a sample, but most would think 100 randomly chosen ferrets for
each age group would give an accurate answer.  Since a cohort age group in
ferrets equals a year, and ferrets live to between 7 and 10 years of age,
that means you will need 200 ferrets for a poor study, or up to 2000
ferrets for a good study.  AND THE BEST IT CAN DO IS GIVE YOU A COHORT AGE
GROUP (= 1 YEAR) PLUS OR MINUS A YEAR.  In other words, you are back to the
"that ferret could be 4, 5 or 6 years old" statement.
 
7) Why 60 ferrets?  If all you need is a skull of a few ferrets of known
age for the photos, you a) don't need 60 of them, and b) you breed and
rescue ferrets and surely must have seasonal losses, so why do you need
ferrets from other people?  If your answer is to get ferrets of known age,
if you actually read my last post on the subject, visual discrimination
will ONLY break ferrets into "tooth wear" categories, NOT "age" categories.
In other words, you ARE NOT ageing ferrets; you ARE lumping ferrets
together who have teeth worn to the same degree.  To be able to prove tooth
wear equals ferret age, you have to show all variables associated with that
tooth wear are identical within the population.
 
8) I suggest, if you are seriously interested in projects of this type,
that you first gain an understanding of the issues and techniques by
reading the available literature for doing the same types of studies on
martens, fishers, mink, weasels, and other carnivores.  Many of those
references will be available on the Ferret Geeks list, but they can be
found through biological abstracts or zoological record.  The best book in
my personal library on the subject is: [Galina A. Klevezal 1996 "Recording
Structures of Mammals: Determination of Age and Reconstruction of Life
History."  A.A.Balkem, Rotterdam.]  Of interest is p. 152 on European
polecats.  It indicates that only sectioning the canine to determine the
seasonal growth layers is useful in determining age, and such a study has
already been completed.  I have the original reference.  It indicates the
wear of teeth is so unpredictable that it is useless in the determination
of age; only the extraction and sectioning of canines is useful.
 
So, Ed, I ask you, what is the purpose of your investigation?  How exactly
are you going to accomplish it?  What new data will it provide?  How can
you accomplish this study without posing a danger to yourself or other
ferrets?  How can you do better than what is already known and published?
How can you ignore recognized limitations on current technique?  These are
legitimate questions *I* would want answered prior to my donation of a
beloved ferret to any study.  Until you can answer those questions, I
recommend NO ONE send ferret carcasses.
 
Bob C and 19 MO' Ferts of Skeptical Science
[Posted in FML issue 2889]