Oats were grown mainly as animal food. The nobles liked to feed their horses oats, because this allowed the horse to spend less time grazing and more time being ridden. With the introduction of the horse collar, more farmers kept horses and oats were an efficient way for them to keep their horses alive over the Winter. And, in a pinch, oats --which grow under less favorable conditions than does wheat-- were a passable food for humans. Or, as the famous exchange had it, "Oats, food for horses in England, but men in Scotland," to which the reply was, "Aye, and where do you find better horses or finer men?"