Don't feed poor-quality hay to young, growing horses and broodmares in late pregnancy. Mature horses normally need about 2 percent of their body weight as hay or pasture. So a 1,200-pound horse should receive about 24 pounds of hay. Limiting forage to less than 1 pound per 100 pounds of body weight can result in digestive problems. Feed 1-2 pounds of hay per 100 pounds of body weight.
Some owners feed grain or commercial horse feeds and less hay to stretch hay supply.
Normally 1 pound of grain replaces 2-3 pounds of hay, depending on the quality of hay. It may be cheaper to feed a single grain like oats compared to commercial feeds. Check the price. Oats is a high-fiber feed that's important if you limit hay intake. Oats is the safest grain, too.