I would recommend Royal Canin's Maine Coon food. It is intended for
larger cats, and it has glucosamine in it, 3 times as much as the
senior feed, and I can tell you that the senior feed did wonders with
Maynard. For months, he begged to be lifted up onto chairs, and since
switching to the senior food last October, he went back to getting up
on his own, even got on the kitchen counter to eat my mom's shamrocks
(left a pot of green sticks). He also took the stairway better.

I went off the senior food for a week once, and it showed. He started
going slower again, and then better when I got more of the food. I
would definetly recommend it.

If you'd like to try a sample of it first, you can check out a local
cat show. They often have a rep there with samples, or I can mail you
one. They gave me two sample packs of the Maine Coone at the last show.
One was a pound bag, so I have been mixing it with Jay Jay's feed. He
really likes it. I sprinkle it i with his favorite food, and he sits
there and picks those first.

I'm going to another show next week, so I'll just go ahead and buy a
big bag (they're a tad cheaper directly from the rep). I won't need the
sample.

Your best bet to confirm your suspicions is to take Ruf to the vet and have
him examined.  My cat (also a large boy) developed arthritis in his back
that became so severe over time that it resulted in a spinal compression
which had to be corrected with major back surgery.  If it is arthritis, you
can get him on a glucosomine supplement like Cosequin (even though the
research I've done says glucosomine really doesn't help spinal arthritis).
But it certainly can't hurt.

S.