I have a 4 1/2 year old healthy male cat. His previous owners gave me a big bag of hills prescription diet c/d for urinary tract health which I plan to use up but the bag is getting low now. As far as I know he has no health problems. his old owner basically said they'd rather spend more money on cat food than future vet bills (which I agree with). Is this the best kind of food for him though? The first 5 ingredients are brewers rice, corn gluten meal, chicken by product meal, pork fat, then finally real meat, chicken. I don't know a lot about feline nutrition but that doesn't sound too good to me?? He has only ever eaten this dry food but I'm planning on slowly added wet food too. I just don't know if I should change his dry food or keep this if it keeps him healthy and he likes it? Does this prescription stuff actually work or is it like snackwells cookies for humans? Marketed as healthy but is actually just junk.