I use a Ration Balancer for my hard keeper (Seminole Equalizer) and for my pony I use Smartpak EZ Keeper Grass. I like the Smarpak because I don't have to think at all about it and she looks good. There are a lot of suppliments out there. It's best to figure out if your horse likes pellets, granules or meal and then pick one based on what you think your horse will eat. At my feed store the manager has little snack bags and you can buy a few ounces of a suppliment and try it. Also, Smartpak will let you have a trial pak or two, I believe. I've even seen some TSC stores have samples, but not very often. It's good to try some out because if your horse won't eat it, then it's just a big waste of $.