Hmm. Do you have a reference for that? From what I have read, Clydesdales are fine on good pasture (hay in the winter), but they won't be able to do much if any work if they don't get additional feed. They would also likely not be as muscled as a horse with supplemental feed. A clydesdale raised on pasture only might also end up smaller, but they won't starve to death, assuming it is quality pasture.
I'm talking about a large breed raised on grain and then suddenly switched to pasture -- not one raised on pasture its whole life -- as you might see with a retired working animal. They may not literally starve to death, but they will lose a lot of muscle mass and may get sick and die from that, or may struggle to survive the winter.
