That's why the amount of food a horse receives varies according to the activity it performs, age, breed, weather, quality of food it eats, the quality of its habitat and the condition of its teeth. They also eat hay, oats, barley, corn, bran, molasses, alfalfa and concentrated foods, based on cereal grains. The horse drinks large quantities of drinking water; needs between 20 and 40 liters per day.