Just pasture when its available with a good mineral block.
In the winter I feed local grass hay along with a feed mixed by a local mill - forage pellets, oats & corn at 11% protein (how much depends on the horse - very little for the haflingers, more for the younger horses) and usually a general vitamin. I used Dumor that came in a big bag this past winter. The local mill stuff is 100 lbs for $16 and the vitamins are $25 per bag. I like to keep things simple and it seems to work.