I do have one. Except he's fat now and has turned into an easy keeper (I think mostly he can't be in a big herd or he stresses all his weight off).

To fatten him up after bringing him home, I was feeding pasture and then Buckeye Ultimate Finish 25 and a "fat and fibre" grain on a 50/50 mix (he eats really slowly and I don't have time to put him in to eat for hours...). It was a good mix, I could feed relatively little and he gained weight quickly.

http://www.buckeyenutrition.com/supplements/ultimate-finish-25.aspx

Now both horses are fat, so they are off grain. They have hay, but are still mostly out grazing whats left of the grass (3 horses on ~10 acres). When there is no grazing left, if they start to lose condition I'll put them back on the fat and fibre (store brand).