Mixes made by respectable feed manufacturers are very good. If you are feeding only a few horses or do not want the hassle of always having to check the nutrient levels of your feed, commercial mixes are a good way to meet the needs of the horse. However, you need to know which commercial mix to buy to match the feeds that you may already be feeding. If you are raising foals, you may want to also add 15 lb. of brewers dried yeast per ton of creep ration to provide B vitamins. Table 7 lists the vitamin requirements for horses.
Grains are high in phosphorus, low in calcium.
Legume hays are high in calcium, low in phosphorus. Grass hays are correct in the ratio of calcium to phosphorus, but are too low in both for horses under two years of age and pregnant or lactating mares. Therefore, if you are feeding pure alfalfa hay, you may have an incorrect mineral ratio and may need to supplement the diet with more phosphorus. Some horse feeds are made to feed with specific types of hays to correct this problem. Table 5 lists minerals commonly used to balance the calcium-phosphorus ratio.