What is the difference between hay and straw?

Hay consists of dried grasses and herbs harvested from meadows. It serves as staple food for pure herbivores and should always be available.
Hay is not only important for herbivores, seed-eaters also need it, especially to promote natural tooth abrasion. Due to the lower energy content of hay and green fodder compared to seeds, for example, herbivorous animals need to consume larger quantities to fulfil their energy requirements.

Straw is an agricultural by-product consisting mainly of the dry stalks of cereal crops such as wheat, barley, oats and rye after the grains have been harvested. Straw is used as bedding, but is also eaten by rodents.