That's right, you incredibly bright person, you.  It means you can feed a
low protein diet and make cystine stones, or feed a higher protein diet
and not make stones; ultimately the deciding factor is the concentration
of cystine in the urine, which means it all centers around hydration.
Because kibble is a dry product with a maximum of 10% moisture, and the
number one treatment for cystinuria is a high intake of water, eating a
dry kibbled diet can contribute to dehydration.  You could be eating a
product with only 25% protein, but if it sucks water out of your
bloodstream to rehydrate the kibble, you could drop the specific gravity
of the urine enough to cause a precipitation cascade, building cystine
stones.  Meat, on the other hand, is between 60-75% water, so even though
it has a higher protein level, the demand for water is lower, so there is
less of a likelihood that a cystine precipitation cascade will result.
In all fairness, I should point out the most dangerous food of all would
be high protein kibbles because you get the double whammy of high protein
and dry food.  However, using the word "dangerous" to describe high
protein kibbles is only valid when used with ferrets diagnosed with
cystinuria; it is not a danger in normal, healthy ferrets--not all.
 
So, why do I know cystinuria is not a widespread genetic trait in
ferrets?  Because it is probably either an autosomal recessive trait
requiring two copies of the bad gene, or it is X-linked, meaning a lot of
males would show the disease in a very high ratio over females.  While
most of these cases are inherited, it is possible a chance mutation could
cause it in an individual male, not having a second X-chromosome to
resolve the problem.  In any case, if this problem were in the general
ferret population, you wouldnt be hearing about a couple of cases, even
ten of them; they would be as common as adrenal disease or insulinoma.
Cystinuria is common problem in dogs because it is widespread throughout
the gene pool of 60 different breeds.  Remember, it is NOT protein that
causes the problem; its a function of acidity and concentration of
cystine in the urine.  ANY ferret with cystinuria would form stones if
they were sufficiently dehydrated.  Think of how many albino ferrets
there are, and that trait inherits exactly like the most common form
of cystinuria.  If cystinuria were in the general population, you would
have an incidence of the disease that would equal or exceed the diseases
we are familiar with today.  We don't, so it cannot be in the general
population.
 
The only possible explanation for the small number of reports is that
whatever is driving this inherited disease, autosomal recessive or
X-linked recessive, it remains relatively isolated from the general
population.  As I said, it is not a problem that worries me in the
slightest.  You treat the sick ferrets without punishing the rest.
 
Now, to sweeten the pot, I made a long-distance call this morning to an
expert in cystinuria to ask for some tips in small carnivores.  The
person was very interested in any cases in ferrets because they are so
unusual.  I read my previous remarks over the phone, and after a couple
of corrections that clarified what I was trying to say, the post past
their approval.  I specifically asked what steps ferret owners, IN
CONJUNCTION WITH A LICENCED VETERINARIAN, could do for this problem.
The following hints were suggested:
 
1) Try to increase the animal's water intake by feeding liquid food,
soups, and broths; your goal is to double the ferret's urine volume.  Do
not feed dry foods, such as kibble, unless they have been hydrated.  If
your ferret is well hydrated, the treatment of choice, they will probably
not form cystine stones, especially if the urine is slightly alkaline
(see #2).  If your ferret has cystine stones, increasing the water intake
can even dissolve them.  If you cannot increase the fluid intake orally,
it is possible to give fluids subcutaneously once or twice a day.  Make
sure your vet monitors the ferret's electrolytes and urine specific
gravity.
 
2) You can add small amounts of baking soda (sodium bicarbonate), or
better still, potassium citrate to the food to make the urine less acidic
(see #3).  Your vet needs to monitor urine acidity--you want to get it
close to pH 7.5; any more alkaline and you cause other types of stones to
form.
 
3. Do not allow your ferret extra salt; eliminating extra sodium might
increase cystinuria, elevating the risk of stone formation.
 
4. Your vet can prescribe drugs that bind to cystine, such as Tioproin
or Penicillamine, making it up to 50 times more soluble in urine.  Talk
to your vet- -if they care for dogs, they should know these drugs are and
how to give them.
 
5. Signs and symptoms of cystinuria result from the presence of cystine
stones.  If your ferret does not have cystine stones in the first few
years of life, it probably never will.  This is a recessive genetic trait
that results in a reabsorption problem in the tubules of the kidneys.
There is no cure and you have it all your life, birth to death.
 
6. It is not a good idea to limit the amount of protein or cystine in
the diet unless all other methods of controlling the formation of stones
fail.  In cystinuria, not only is cystine spilling into the urine, but
also, so are three other amino acids.  Additionally, because the disease
affects the transport of cystine across cell membranes, not only is
cystine spilled into urine, but it also means there is impaired
absorption of cystine through the intestines.  Reducing protein in dogs
is a useful treatment, but dogs are carnivorous omnivores, while ferrets
are primary, obligate carnivores, and the reduction of cystine, a
precursor of taurine, may have unforeseen redults.  Regulating hydration
and urine pH is a far better course of treatment, and unless it fails,
protein reduction should be avoided.
 
7. Cystinuria is relatively unknown in ferrets, but the causes and
treatments are the same in ALL species that have shown the disease (the
Merck Veterinary Manual details the same basic treatment for all species,
and it matches the treatment for humans).  Nonetheless, all procedures
should be carefully monitored by your veterinarian in cause ferrets have
a physiological quirk that requires modification of the treatment.
 
As I said, it is a disease that cannot be widespread in ferrets, so there
is absolutely no reason to worry about foods with increased levels of
protein UNLESS your ferret shows symptoms of stones.  In that case, see a
vet immediately, and if the stones are cystine, THEN you can worry about
treatment.  There is NO REASON to punish the vast majority of ferrets
because of the illness of a few.
 
Bob C  [log in to unmask]
 
"In that part of the West where Yap Yap the Prairie Dog lives is a
relative called the Blackfooted Ferret who looks like a large Weasel.
He is about the size of Billy Mink, but instead of the rich dark brown
of Billy's coat his coat is a creamy yellow.  His feet are black and so
is the tip of his tail.  His face is whitish with a dark band across the
eyes.  He is most frequently found in Prairie dog towns and lives largely
on Yap Yap and his friends.  His ways are those of Shadow and his
cousins.  There is no one Yap Yap fears quite as much."
Thornton W. Burgess 1920 The Burgess Animal Book for Children.
[Posted in FML issue 4787]