Bob wrote about cystine uroliths:
>This doesn't mean it can't or doesn't happen, but when it does, it
>means the individuals would normally die, and the bad genes exit the
>breeding pool.
 
Exactly!  If the marked increase in rates of cystine stones seen over
the last year and reported by the UC Davis urolith lab and their exotics
clinic is related to a genetic cause (and in many species which get
cystine stones it is a genetic kidney problem, including in several
members of Carnivora with the problem) then the rate will be low in
those populations which have a long history of high protein eating.
 
When this exists in a population which is normally fed a high protein
diet the ferrets develop the stones normally either before they have
bred or before they have bred twice.  So, in a population which has
consistently gotten a high protein diet the number with cystine stones
will be low -- even very low.
 
The chances of surviving to breed once are higher among the females
affected, which can further limit the numbers compared to when males
are affected and are bred to a number of females.
 
BUT what we have among many ferret breeding groups in the U.S. differs
from that.  We have a population which has a large number of generations
of about 35% protein diets.  Just think of the number of years that the
original farms have been breeding ferrets and realize that many of the
smaller ferret populations here also trace back to some extent to those
ferrets.  Those are animals who have been on 35% kibbled diets for as
long as over 20 generations, so there has been plenty of time for animals
with that vulnerability to breed repeatedly.  With the risk factor
reduced the die off would not occur.
 
Add on to that the problem that there was long the assumption that
cystine stones are almost never seen so testing has been low until recent
years, with the assumption made that the ferrets were instead getting the
more common struvite stones.
 
So, now, when going to higher protein diets what is seen is what a person
would expect with a genetic vulnerability: an unknown percentage of
ferrets is winding up with cystine stones and the rate has increased at
the same time that more people are feeding higher protein diets.  That
change in rate leaves many questions to be answered.
 
The ONLY way to know which type of stone is being encountered -- and
therefore what sorts of adjustments the affected individuals need is to
TEST THE STONES, though urine pH can be an indicator since these stones
tend to appear in conjunction with urine that is more on the acidic side.
 
The vets who are studying the increased rate of such stones appearing in
their lab want to hear from vets who encounter such stones, so, please,
make sure that your vets have the contact info in case you or another
client winds up in the same situation we have with two of our own
ferrets.  They are seeking the stones, the histories, and if there winds
up being the chance of having tissue samples those would also be of use.
They are looking to see if they can find the same genetic causes seen in
other species and whatever else they can find out.  This data can only
help ferrets.
 
THIS IS AN OPPORTUNITY.  It is not often that we get a chance to get
an handle on an emerging ferret health problem so that it can be tackled
in ways that have the best chance of saving ferrets' lives.  Usually we
are playing catch-up on common existing problems.  This one is
life-threatening, so making sure your vets have the contact data can
only ultimately help us all best help our treasured ferrets.
 
Dr. Michelle Hawkins VMD DABVP (Avian) is coordinating this effort and
can be reached at:
2108 Tupper Hall, University of CA, Davis, CA 95616
1-530-752-1363 (phone)
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[Posted in FML issue 4787]