You will need to supplement with grains as these are high-energy feeds to be used with hay to regulate the growth, reproductive performance and work. Oats are usually the first to be fed among grains as they are very high in protein and are useful when fed along with low protein hays. If you were to combine corn and oats in equal portions this makes an excellent grain ration. Milo can be used instead of corn and is more economical than corn. Barley is an excellent choice when it is ground and will reduce the chances of colic when fed with twenty five percent oats.
Wheat bran is very bulky and high in protein, high in phosphorus, and also low in calcium.
There are many meals that you might use to supplement the pasture feeding of your horses, such as cottonseed meal as it is high in phosphorus content. Alfalfa meal, meat meals, dried milk products and corn gluten meals are used as protein supplements. Soybean is used more than linseed meal as it is higher in protein and has a balance of amino acids as lineseed meal has a laxative effect and mixed with roughages it becomes very poor quality. You might also want to try some commercial supplements for a specific feeding program. Most of your common farm feeds will provide minerals but your horses will need extra calcium, salt, iodine and phosphorus.