well done mate. they say milk isnt to good for ferrets I wouldnt give it to mine now but have in the past here is a post I just read.
Your ferret may love ice-cream, milk and cheese but these should be avoided. Ferrets are carnivores and are supposed to eat meat protein, they are not designed to process dairy proteins.
In particular, Ferrets lack the enzyme required to digest lactose, a little like lactose intolerant humans. The risk is some messy diarrhoea and possibly dehydration and a visit to the Vet. Small amounts may appear to be fine, but why risk feed your ferret something that