Check out this post- http://fhotd64476.yuku.com/topic/6954
We've had quite a few older guys. so far best results,personally, have been with beet pulp (a large folgers coffee can or three per feeding, 1/2 alfalfa and 1/2 grass (at each feeding), rice bran (we have used about 1 to 2 cups per feeding, but I understand you can use more). And enough Equine Senor (I've been leaning towards Safe choice etc) so they will eat it, ususally 1/2 to one full large Folgers can.

The thing with beet pulp is that you have to soak it!!! ALL the WAY. No shortcuts on this one

If possible feed 3 xs per day.

I have heard anecdotally that daily wormer can be helpful.