How much hay does a horse eat in a day?

Horses need to eat a minimum of 1% of their body weight per day in forage just to maintain digestive health. Most horses need closer to 1.5% to maintain weight and may need up to 3% depending on their activity level/reproductive status. This means that for a 1000 lb horse, you need to feed a minimum of 10 lbs of good quality hay per day.