Tom Willard replied to some diet and kidney health posts, and Bruce
Williams then weighed in with new information:
 
>good questions regarding the proper level of protein for ferrets with
>kidney disease.  We began a limited study looking at lowered levels of
>protein for kidney damaged ferrets a few years ago.  We had problems
>because there was mixed and limited data and information regarding what
>was considered the proper definition of kidney disease or the diagnoses
>for kidney disease in ferrets...
 
>several 8 or 9 week old kits were given an improper antibiotic and
>subsequently destroyed a great deal of the kidney function if not
>the tissue itself in all of the ferrets. This was defined as a BUN of
>100+...
 
>The vet had prescribed the Hills k/d canned diet as the recovery diet for
>the remaining kits.  The owner said after three days the remaining kits
>were not doing well and the BUN's still over 100 +...
 
>[then] suggested that she feed XXXX which had 37% protein and 24% fat
>plus much higher levels of vitamins and minerals than the cat k/d... for
>the kits to recover they had to build new tissue plus their immune
>system.  It would take all nutrients not just protein or vitamins...
>Within two weeks the BUN's were below 40 and after four weeks below 30.
>The normal range is about 20 to 40... the principle is that any time an
>animal has damaged tissue, kidney or other wise it needs proteins of
>high biological value (BV) and a complete nutrient profile of over 60
>nutrients in the proper proportion to rebuild the damaged tissue.
 
Well, I'll weigh in on this a bit, and I have learned a bit myself by
spending some time with the recent literature on restricted protein diets
in animals with chronic renal failure.  There is a large body of evidence
recently that is showing that the effects of protein restriction does
little to preclude the development of renal disease.  What it does do,
however, is delay the onset of uremia in animals with failing kidneys,
and keep BUN levels lower for a longer time.
 
We need to realize that this information is gained in other species, and
under other than natural conditions, in the laboratory with surgically
manipulated animals.  But it is likely that the general principles are
applicable in other mammals as well.
 
Tom - regarding your situation with the ferret kits and the inappropriate
antibiotic (I'll bet a dollar to a doughnut this was gentamicin - a drug
that ferrets are extremely susceptible to) - this represents a case of
acute renal failure rather than chronic renal failure.  The levels of
protein probably had little or nothing to do with the survival of these
animals - in drug-related acute renal failure, survival is based on
regeneration of the injured epithelium (which, if the basement membrane of
the tubule is preserved, will usually occur as long as there is sufficient
uninjured renal tissue to keep the animal alive) rather than the prevention
of injury to the remaining nephrons, which is our current rationale for
protein restriction in CRF.  You are correct however, in that a high
quality food may help animals in this state to regenerate lost tissue more
efficiently and quickly.
 
The bottom line is that for aging animals, our long-standing belief that a
protein restricted diet will prolong renal health is probably inaccurate.
(In fact, phosphorus content may be more important in the diet than the
level of protein.) Additionally, as protein restricted diets are generally
less palatable, older animals on low protein diets may actually take in
less calories as well, and may achieve poor nutritional levels overall.
But for animals like Champ, who is already in documented renal failure, a
protein-restricted diet very well may stave off the signs and symptoms of
uremia for a while longer.
 
With kindest regards,
Bruce H. Williams, DVM, DACVP
 
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[Posted in FML issue 3371]