Check what you are feeding.  An active ferret requires 18 to 22% fat with
a range of 33 to 38% protein with 85% coming from animal sources such as
chicken-by-product meal, chicken liver meal, eggs, chicken or poultry by
products.  Just adding fat supplements or vitamins is not as effective as
when included in the food.
 
Sincerely,
DR Tom Willard
[Posted in FML issue 3399]