I don't know how to keep my wolves at a lower weight. Whenever they get low in hunger I feed them, so the pack happiness stays up, but then they get overweight.

How do I make them not so heavy, but still keep their hunger up?

A wolf's weight is set in stone the moment it is born/created, and as of right now there is no way to change it. Pups take 24 real life days to reach their final weight, also.

This is the weight chart from the Game Guide:

75-89 +5 Agility -2 Damage

90-109 +2 Agility -2 Damage

110-129 -2 Agility +2 Damage

130-150 -5 Agility +5 Damage.