If hay is scarce, you can feed 2-4 pounds of grain daily in place of hay. A pound of grain will replace 2-3 pounds of hay. Don't feed legume hays, such as alfalfa, or high-protein feeds. These increase water intake. Horses, especially in hot weather, need loose, trace-mineralized salt.
Loose salt is better for horses than block salt, but block salt is better than no salt.
Use the blue or red salt instead of plant or white salt. Horses need about 3-4 ounces of salt daily in these weather conditions. Horses not accustomed to salt may eat rather large amounts. But this normally doesn't harm them if they have ade quate water. After they have had salt for a couple of weeks, you can place a larger quantity of loose salt out so you don't have to feed it daily.