welcome to the forum
I feed my horses grain free, with alfalfa/ grass pellets as base, ain't depending on horse, the Arabian gets about half a kilo, the much larger TB mix 2kilos, then I add, per day,3 tablespoons iodized table salt, 100g flaxseed, magnesium oxide, 5g for normal, 10g for the insulin resistant horse, 2 cups of rice bran for the hard keeper, and a mineral/ vitamin mix especially for our area here.
To add calories/ energy I would add rice bran or beetpulp, or both, if needed. Beetpulp has about the same energy as oats, ca.1200 calories per lb, ricebran is a bit higher, it contains more fat.
All that on top of free choice grass hay and a flake of alfalfa .
I found I cannot feed any ration balancer, they all have added iron, and we are high iron here already, and iron is believed to play a role in insulin resistance.
it would help if you would tell us the breed of your horse and what ration balancer you have available, so we can give you more detailed info