I'm a little behind in reading the FML, so this may have been answered
already, but here's what I know (as a vet) about milk thistle... It is an
antioxidant and is useful in chronic liver disease as are vitamin E and
Sam-e.  As far as a dose for ferrets... that would be hard as they are not
sure of a dog dose yet - as far as I know, no big studies have been done
figuring out efficacy and dosages yet.
 
Hope this helps!
[Posted in FML issue 3152]