I am just catching up on the FML, and I think you may have misunderstood Dr.
K's comments about taurine.  Dr. K is one of the foremost vets studying
degenerative retinal disease, and he may have suggested that ONE of the
causes is lack of taurine in the diet, and he should have ruled that
possibility out for you because you feed Up a premium quality pet food.
MEAT is a natural source of taurine and Iams is a premium quality meat based
food.  I have never heard of any vets recommending a taurine supplement for
an animal being fed a premium diet, so I would tend to think your ferrets
optical problems are genetic, not diet-related.
 
Call Iams and ask what the percentage of taurine is in the package.  They
don't state it on the label because it's naturally occurring and in
sufficient quantities for cats.  If it's sufficient for cats, wouldn't you
be able to extrapolate that info and assume that it would be adequate for
ferrets even if they required a higher quantity?  (You can't get higher
taurine than pure meat content in a feral state, why would a domestic state
of ferrets require higher taurine?)
 
The # for Iams is: 1-800-525-4267.  They'd be happy to provide you with
their feline research, but I don't think they'll have any specific mustelid
information.
 
The other place you can check, is a state/provincial/national veterinary
school.  They can tell you what their ferret diet formulation consists of
and why.  I know that the U of Saskatchewan in Saskatoon was testing a
corn-based diet.  Why, I have no idea, but you could certainly ask them.
 
-=-=-
[log in to unmask]
The Territorial 3 and the Kitty (what rhymes with 3 here? hmmm)
[Posted in FML issue 1536]