Scratch is a grain mixture. In the times before commercial feeds farmers would mix it from the grains they had at hand. The corn doesn't have to be cracked. And scratch may have no corn in it, most do.
Don't believe it when others say it has no nutritional value. The without thinking reaction is to say it's like feeding them candy. It is more like feeding them what whole grain bread is to us. You can live on just whole grain bread, but after a while its deficiencies begin to show up. In fact if you find the list of ingredients in feed, most of it is the grains that make up scratch.