@
JonLosAngeles66 I'm sure major veterinary schools have resources to help with this, and your local vet.
The caveat is that even food labels cam be very misleading. A neighbor has had a string of Golden Retrievers, and one particular one, years ago, had a lot of painful walking. One day, he was walking with the neighbor and it was obvioys he was doing MUCH better.
The change? The neighbor went from a
Science Diet product to a much cheaper, basic
Purina product! I don't know what the food differences were, but the joint pain changed DRAMATICALLY.
You might start by looking at ingredients of better cat foods and seeing how you could replace the crappy "fillers"--<x> meal, etc.--by a better substitute.
I'll bet cats likely need roughage, but I'm not sure how they get it; dogs eat a much wider set of things. I feed my cat one meal of tuna (for people) each day so that he gets something NOT kibble, but meat. He'll also eat some squash (acorn, baked) and some yogurt, so he's had some variety there.
Besides the cat who lived to be 21, I have also had dogs live very long.