The standard word is that a draft horse should be fed a minimum of 2-3% of their body weight each day. Depending on the size of the horse, draft horse range from about 1600 lbs to over 2000 lbs. At 1800 lbs, that would mean feeding between 35 and 45 lbs of feed a day. It is not unusual for an owner to feed about 1/3 to 1/2 of a square bale of hay to their horses twice a day depending on how much the horse is working and also what other feed is being provided. Since these are work horses, the amount of work they are doing will determine how much they need to eat.