It's a common occurrence for a ferret to get hooked on Duck Soup when they
are sick, so that they don't want to give it up when they are well.  What we
found works in most cases, is to slowly decrease the amount of other
ingredients, while increasing the amount of the dry food.  Pretty soon you
are serving moistened ferret food, then dry ferret food.  Do it as slowly as
necessary, but you will get them back to their dry food.
 
Dick B
[Posted in FML issue 1744]