He doesn't seem to get filled up on the
cat food, and the vet suggested that I not
feed him canned food.

You need to find a new vet. A cat with CRF should not be fed *dry* food.
A canned diet is a very important part of treating a CRF cat. Moisture
is extremely important and dry food does not even come close to meeting
a cats water requirements. Cats are poor at making up the difference and
shouldn't have to. You might want to join the feline CRF yahoo group and
ask for a vet recommendation for your area.

http://groups.yahoo.com/group/Feline-CRF-Support/

Your vet is doing your cat no favors by telling you not to feed canned
food.

Megan



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