Hi,
 
Real whipping cream is high in fat, so it could be used to help an animal
gain weight.  But it's also a dairy product, which means that it is
difficult for the ferret intestine to absorb, because ferrets are
basically 'lactose intolerant.' (Ferrets, however, will try to tell you
otherwise--mine try to help me eat ice cream.) I suggest using something
closer to the ferrets normal diet (but please do get your vet's opinion).
 
Proven weight gain food: My sick (pathetic bag of bones) ferret had been
suffering from a chronic intestinal inflammation.  I put her on plain,
unmodified Gerber's Babyfood Chicken, at the suggestion of Dr. Bruce
Williams.  This stuff is easily digestible for ferrets and most of 'em like
it.  In less than a month, the ferret literally DOUBLED her weight.  We
keep a supply of it on hand now for sick fuzzies.
 
Untested hypothesis: Ya might try a small amount of vegetable oil.  Once I
spilled some olive oil and my fuzzies thought it was a nifty new treat.
(And a nifty new way to mess up the kitchen floor.) (I also suspect ferrets
would like plain, old-fashioned lard.)
 
Regarding ferret health in general, I've seen a lot of questions to this
list that make me think the following web address isn't as widely read as
it could be --it was a lifesaver for my ferrets--
http://www.afip.org/ferrets
This site is written mainly for veterinarians about ferret diseases, but
it is crammed with information and answers all sorts of questions about
medical issues.
 
Good luck!
Jacqueline
[Posted in FML issue 2592]