>Okay, like, I don't get it!  Like (I love saying "like"), ferrets are
>obligate carnivores... So how would feed slightly higher in protein
>percentages be able to do this?  The highest protein content I know of
>in food is 50%.  Considering ... it just doesn't seem all that high.
 
The protein level in a mouse cadaver is a tad higher than 50%, BTW, if
memory serves.
 
Okay, here is the thing.  There is a genetic condition which is seen in a
range of mammals which cause those mammals' kidneys to have an especially
hard time with some of the amino acids.  (Amino Acids are the building
blocks of proteins.) Some ferrets have trouble with just cystine, others
have trouble with what is termed the "COLA" group" of 4 amino acids:
cystine, ornithine, lysine, and arginine.  With that genetic variant the
individuals can handle just so much of these aminos acids before their
bodies wind up creating stones and having increasingly acidic urine.
 
There are other species in whom the condition would show up at lower
protein levels but in ferrets this type of stone have been very unusual
until recently.  In the last year the rate of cystine stones has
increased markedly.  That is why the levels of these amino acids which
are accessible to the individuals, the urine, the blood, the stones, and
when the individuals are lost the kidneys are important to study -- to
see if it is this genetic vulnerability, to see if the individuals are
having trouble with just cystine or with other COLA amino acids, etc.
 
This vulnerability can be very hard to manage.  We've been lucky.  Our
two have not (so far -- in about 6 months) has recurrences.  Morny made
out well with her's even though it was very large (asymptomatic until
she became constipated and then we found that her bladder was holding a
stone that took up most of her bladder).  Hilbert was more complicated,
partly because he had a bladder deformity, and partly because he wound
up with small stones in his urethra so we came close to having to bypass
his penis (but luckily cystos worked).  In his case his condition caused
bilateral hydronephrosis and for a few weeks he was able to be kept
alive, so we are especially fortunate to have him with us today.
 
Those who aren't as lucky have to have a diet which is more reduced in
protein or they need to have a couple of medications which can be very
tricky because of serious side effects being very common with them.  As
of 6 months ago there was exactly one journal article out there right now
on managing this condition in ferrets; if memory serves it is by Mike
Dutton though I believe that Thomas Kawasaki has also managed a ferret
for 6 years who needed medicating to stay alive, and many vets are having
to suddenly learn with the incidence increasing.  The meds used are
Tiopronin and Policitra-K.
 
The rate of U.S. ferrets who will develop cystine stones when not on
the older style of diet is unknown at this time since higher than 35%
protein diets are quite new here.
 
There are over 60 breeds of dogs who are prone to these stones.  Here
is an article about them in Newfoundland dogs which explains a bit more
about the genetic condition:
 
http://www.vetprof.com/clientinfo/newf-cystinuria.html
which begins:
 
>Cystinuria is an inherited disorder caused by a defect in the
>transport of cystine, an amino acid, in the kidney tubules.  Normally,
>cystine that is filtered in the kidney is reabsorbed within the
>tubules, resulting in little cystine in the urine.  Dogs with
>cystinuria do not properly reabsorb cystine (and a few other amino
>acids) in the kidney tubules, causing the urine to contain abnormally
>high levels of cystine.  Cystine is insoluble in neutral pH or acidic
>urine, so excess urinary cystine results in formation of cystine
>crystals, which in turn can lead to formation of cystine calculi
>(stones) in the kidney and/or bladder.
 
There are a lot of articles about them in dogs and humans.  This genetic
condition has also been identified in some types of cats and in maned
wolves.  In dogs it is an autosomal recessive trait caused by a mutation
in the renal Basic Amino acid Transporter rBAT.
 
The new study on these stones in ferrets is being
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)
[log in to unmask]
 
With the help of specimens and histories from ferret veterinarians we
will hopefully have solid information soon to help save those ferrets
who find their kidneys unable to cope with their diet.
[Posted in FML issue 4755]