Straw is the stalk that is left after the harvest of grains. Could be wheat, rye, barley, oat. ..straw. Often there is some missed or loose grains but not enough to add much. Hay on the other hand is forage harvested hopefully at optimum maturity. High in protein, low in fiber, high in vitamin and minerals, tender and tasty. Rich in beta carotines that keep the yolks a bright orange. Straw is a bedding. Hay is a feed.