Just a few points, which I expect Bob will mention himself later on anyway
since he's inclined to be astonishingly thorough in his investigations.
Still, these might be useful for some folks now since the question have
already come up.
 
1. We had to go entirely to homemade food at one point for furry with a
special condition.  Here is what the veterinary nutritionists told us to
make: Cook a turkey with some assorted veggies and loads of water.  Skim
off as much fat as you can and reserve.  Eat some of the meat and most (but
not all) of the veggies yourself.  Recook the bones till the ends are soft
and pulverise those ends to a powder.  (With a very, very young bird such
as a chick whose bones have not fully calcified I'm betting that all could
be used as is, ditto new-born mice.  That said, I once had to give baby
mice regularly to some herps I was raising for a prof and don't want to do
that again.) Put skin, meat you didn't eat, veggies, reserved fat, powdered
bone, cartilage, tendons, nerves, etc., plus some hard boiled egg yolks
(They specifically said "yolks" not "whites" and not "whole eggs".) and
Brewer's Yeast into blender if ferret won't eat them in pieces.  Try rough
grind first, but puree if you have to for acceptance.  Garnish with a few
raisins and cranberries.  These days, after learning from Bob's recent
posts I think I'd add extra taurine on top of what is naturally in there
simply because I am not providing them with insects or brains.  (Not joking
here.) Then you can add a tiny bit of salt or Nusalt depending on ferret's
needs and wants.  (As a ducksoup base you can then add whatever your ferret
needs for a given problem.)  It cubes well in an icecube tray in the
freezer.
 
2. Mortality states don't exist in the number needed to have nicely solid
data on lifespans and causes of death in wild with polecat species, and they
surprisingly don't exist in good reliable form for domestic ferrets, either.
 
3. Ages (unlike age categories) can be hard to estimate in an animal which
has been severely ill or suffered exercise deprivation.  You've seen this
yourself in humans.  I used to have a friend who was a concentration camp
survivor.  She looked 70 to 80 from about 35 through 65.  My mother at the
end of her cancer looked 30 years older than she was, and a friend's mother
in that position looked 80 at 40.  This can happen in ferrets, too,
depending on the illness, if it is treated, the animal's genetics, how ill
the animal gets, any recidual damage, etc.  As a result when diet is studied
it will be important to use only animals which have been studied from
kithood, since a rescue could be either older, or younger than thought, even
though the age RANGE is likely to be determinable.
 
4. When discussing needs of the very old (In humans that translates to 75
and over; in ferrets my guesstimate would be at about 8 years of age.) many,
many many of the rules INCLUDING NUTIRTIONAL ONES just fly out the window.
For humans: more of certain nutirients (such as vitamin D) are needed, some
other things start causing the body to over-respond and need to be reduced
(This is already known with strong data for a number of meds but it might
also be true for some things taken in diet.), some things are more of a
hazard statistically in younger years (such as high fat consumption).  With
humans the single BEST thing so far (from EXTENSIVE studies with thousands)
for longevity seems to be exercise and plenty of it -- BOTH of aerobic and
weight bearing types (Translate this in ferrets to plenty of running,
digging, game playing, wrestling, stretching up to find treats hidden in
"high" places, climbing, jumping, carrying, etc.) The point here is that
what keeps a younger ferret at optimal health might not turn out to be the
same as what keeps an old ferret at optimal health -- maybe not even a
young-old one (In humans this is considered to be about 60 to 65 on to about
75; In ferrets I'd guess at about 6 years.) so data need to be accumulated.
Take into account here that the elderly of all species are prone to more
health problems so programs need to be designed around individual needs,
also take into account that exercise also helps intestinal function (as well
as heart, sugar balance, bones, etc.) greatly in humans and should do the
same in all mammals.
[Posted in FML issue 2315]