I am not sure if I have my info correct or not, so hopefully someone else knows more but, I think I heard cat food has more fat then dog food. A dog can survive on cat food, although it is not the best for them because of the increased fat and oils, but a cat can not survive on dog food.

I would try to change your dog over to dog food by mixing the two, slowly decreasing the amount of cat food. You may try using a "wet" dog food, as it is strong smelling and may be more interesting to the dog.