I've been researching what to do with sick animals and I read that flaxseed oil mixed with cottage cheese will help with a lot of ailments, particularly with older animals. Mix one tablespoon refrigerated high-quality flaxseed oil with 2 tbsp organic cottage cheese in a blender until the oil is completely blended. You can mix with a little water. Google Budwig Diet for more information.
Also co-q-10 can help as well. You might try those things before switching his diet around. Not all animals will go for a raw diet and you can't force them.