As you know, my habit when I don't have enough info to figure that I can
provide a definitive answer to a question or come to question what I had
accepted is to ask an expert.  Below is from Dr. Tom Willard whose
doctorate is in animal nutrition.  I learned a LOT from this and hope
that you also will.
 
   [Begin Dr. Willard post:]
 
Kidney Disease and Diet
 
This is not intended to be a complete review paper regarding kidney
disease in carnivores or ferrets but only to bring up several points
which are know about the kidney of different species and to make
recommendations regarding the diet of carnivores.
 
I would have to say in my 30 years in the pet food industry and over 10
years in working almost exclusively with ferrets in both nutrition and
research, that renal failure - cause and effect - is possibly the most
misunderstood and mistreated disease in companion carnivore pets.
 
First, we need to define chronic renal failure.  According to Dr Gregory
Reinhart, PhD and Director of Strategic Research, R&D, The Iams Co., it
is the sum effect of a wide range of diseases that results in loss of 75%
or more of the functional parenchyma of both kidneys.  In chronic renal
failure, this loss of function is progressive and irreversible.  Further,
it is associated with a gradual decline in glomerular filtration rate
plus an accumulation of protein metabolic byproducts such as BUN and
creatinine.  Increased severity of histological lesions and development
or worsening of clinical signs (pg 395)_.
 
Dr Delmar R.  Finco, DVM, PhD, DACVIM Professor in the Dept. of
Physiology and Pharmacology Medicine, U. of GA has conducted extensive
research on both dogs and cats regarding the influence of protein one
renal failure over the past 20 years.  In the 1998 Iams Nutrition
Symposium Proceedings_ (pg 413), Dr Finco presents a paper on the
Influence of Protein and Energy in Cats with Renal Failure, states in his
summary: "It is concluded that restricting protein in cats with chronic
renal dysfunction for renoprotective purposes is questionable, unless
more convincing evidence of harmful effects is provided".  He goes on to
elaborate in his presentation that progressive renal failure is a common
cause of death in cats so slowing its progress will prolong the life and
add to the comfort of the animal.  The same would obviously be true for
ferrets.  But Dr Finco goes on to state, "contrary to a previous study,
results did not demonstrate adverse effects of protein ingestion on
glomerular mesangial matrix accumulation, even when amounts consumed
were greater that previously shown to be injurious".
 
There have been studies on dogs that have shown that there is no
relationship between protein intake and progression of chronic kidney
disease seen in rats, according to Dr Gregory Reinhart of The Iams
Company_.  Dr Reinhart goes on to state that there is no evidence that
feeding moderate protein diets to either dogs or cats relative to
severely protein restricted diets contribute to progression of chronic
renal failure, the rational for excessive protein restriction is even
more questionable in these species.
 
Most of the misinformation regarding the benefits of feeding protein
restricted diets has come from a poorly designed study over 35 years ago
pertaining to laboratory rats with kidney disease.  Not until Dr Finco
began his research on dogs in the late '70's and early '80's and later on
cats, using the remnant kidney technique, which he developed, did factual
information become available on carnivores regarding the effect of
dietary protein levels on kidney disease.
 
In an uncontrolled and unreported research study, which we conducted
during the mid '90's on ferrets, we demonstrated a positive effect on
eight-week-old ferret kits who had suffered kidney damage and exhibited
extremely elevated BUN levels.  We fed our current Totally Ferret diet of
37% protein and 23% fat to all nine kits and 4 of the 5 recovered whereas
the 4 kits fed a low protein, low fat diet (30% protein, 16% fat) all
died.
 
Based on all of the information I have reviewed plus many of our own
studies, restricting the protein intake on an obligate carnivore such as
a ferret is contraindicated.  Not only will the essential amino acids not
be available for tissue rebuilding in the damaged kidney, there will be a
lack of all of the essential nutrients for immune system rebuilding which
will open the animal up to secondary infection.  This includes feeding
special prescription cat diets designed for kidney dysfunction.
 
As previously stated, this is not a lengthy review article on kidney
disease of carnivores in general nor ferrets specifically; it is a
presentation of some specific information as sited above regarding dogs
and cats.  There is little or no direct research information on kidney
disease in ferrets which I am aware of so we can only attempt to draws
some cross species conclusions.  I do however, suggest that any
veterinarians diagnosing renal disease in ferrets at least consider that
ferrets are a more restrictive carnivore that cats and according to the
available research in cats restricting protein is contraindicated for
disease symptoms mitigation _.
 
I will be happy to further discuss this with anyone involved in
research on ferrets as our company is always interested in advancing
the nutritional and healthcare knowledge of the domestic ferret.
 
Thomas R. Willard, PhD
President
Performance Foods, Inc.
[Posted in FML issue 4153]