I see some muscles :) Hae you put him on some pro bios and maybe some acedophilus(sp) Or had him checked for ulcers? I know lots of people scream ulcers first thing, but they really are more common than folks might think. Anyways.... Good luck and consider maybe a senior feed through winter. Hey are made to aid digestion...he might get more out of it. Oh and maybe try some stuff called red cell. It's awesome for helping stabilize their weight and gain a few pounds.
"Light travels faster than sound. That's why some people appear bright until you hear them speak."
Larry the Cable Guy