Why do you think that 3 lbs. is fat for a male ferret?  I think this is
normal or even a little underweight for a male.  I wouldn't even be TOO
concerned if a female was 3 lbs top weight.
 
From what I have read, females are normally 1.5 to 3 lbs and males are 3-5
lbs.
[Posted in FML issue 1854]