I have NOT encountered or heard of an unusual number of shortened life
spans in ferrets who have clean mitts and bibs (the first type of fancy I
ever saw, and they wanted $400 for him back then in the 80s so he didn't
come home with us), marked whites, dark-eyed whites, or the standard
polecat ferrets or albinos.  The ones I have heard of with shortened life
spans (pandas and blazes) have the markings of WS, Kitt, or one of the
other neural crest pigment disorders.  Sadly, their genes have become
present in may lines.
 
I also do suspect that some of the infectious diseases that ferrets can
get that weren't present back in the old days may play a part.  After
all, we already know that there is good evidence that a precursor virus
can be present in some cases of lymphoma/lymphosarcoma; a project was
reported by someone else (but I guess that perhaps it didn't get funding
because word of it dried up?) to see if there might be a viral precursor
for some adrenal neoplasia cases, we already know that ECE can be a
precursor of some problems such as IBD, etc.
 
You know, thinking about how things like Meow Mix didn't show any
evidence of hurting back then in our experiences and apparently that of
others (good health, long lifespans) I am wondering if we should consider
reading up on them and maybe including them in our mix of multiple high
quality foods that we give to give a bit more variety.  (Sacrilege!)
Like the many others who have reported in from the old days we didn't see
worse health from the diet in the days of Meow Mix and raisins.  (I would
not give that in a combo for any sick ferrets, elderly ferrets, etc.
though, if I try it.)  I do recall that those foods were not as kind to
skins and coats and did result in more feces because they are not as
dense for nutrient packing.
[Posted in FML issue 3954]