Definitely talk to your vet when you see him/her next.
I would be giving him a specific diet and supplement, with 100% turnout time. Turned out with just a couple of low-key friends, only stalled to eat.
Grass hay or Timothy hay, as much as he can eat.
Little to no grain. If you want to feed grain, something like Triple Crown Low Starch. But really, I'd make your own grain using alfalfa pellets (1-5 lbs daily), a vitamin supplement (like Select II
or Uckele's Equi-Base Grass
), and some flax (I like Nutra-Flax
, 1/2 cup to 1 cup daily).
This is a low-key diet, to help his metabolism return to normal and create a calmer horse, but with plenty of energy to ride.
For supplements, I'd have him on something that contains glucosamine, vitamin C, chondroitin, MSM, and Yucca. Along with the shots you're giving him. HorseTech.com will custom blend you something, along with extra flax, so you can have it all in one bucket. I've had good luck with their products.
This one has everything by the Yucca: View Cart
This one has everything by Yucca, plus it has extra flax, biotin, probiotics, etc.: Quick Links
If you're feeding him corn oil, stop. It has shown to increase inflamation in arthritic horses.