Do horses need to be fed grain?
Provide plenty of roughage
Many pleasure and trail horses don't need grain: good-quality hay or pasture is sufficient. If hay isn't enough, grain can be added, but the bulk of a horse's calories should always come from roughage. ... A horse should eat one to two percent of their body weight in roughage every day.
Why do horses eat grain?
Why We Feed Horses Grain
So why, then, do we give them grain? When horses are in work, are hard keepers, or are nursing broodmares they have additional energy requirements that may not by met with quality hay or pasture grass alone. We give horses grain-based feeds to meet this additional caloric need.