Do you want the short, simple, and sweet answer to whether or not you should feed ducks bread? No, Nada, Never - comprende?
Ducks don't strike most people as winter animals. That being said, they're extremely hardy. With proper preparation, you can raise ducks in the winter.
Why would anyone choose to raise waterfowl? No, I'm sorry but the real question is why wouldn't anyone choose to raise waterfowl!?