Why do horses need roughage?

Roughage is what horses are designed to eat. Roughage's include grass, hay, haylage, and chaff. Grass is what is natural for them to eat, but in captivity horses have adapted to hay and hay products. Roughage is what keeps the horses digestive tract working. Horses need to graze about 16 hours or more a day to keep their stomachs at the right level of fullness to prevent acid build up which causes ulcers. Lack of roughage in the diet can lead to multitudes of problems from stable vices to death depending on each situation.