I might be wrong about this. But in my experience, especially with my mini rex they seem to chunk up on the pellets. The hay helps them to feel full, without adding the pounds. This works great for us. I have two juniors that looked a bit chunky to me at three months. they where weighing 3.3lbs and 3lbs. But they had bellies on them, and you could feel the extra fat on them. They went to only 1/8 cup of pellets a day and free choice hay for a week. Now I have them at 1/3 cup pellets and free choice hay and I think they are looking good. I usually free feed my juniors till a bit after 3 months, but I may not do that with my mini rex in the future.