Hay is generally cut from fallow fields in late summer/early fall. It contains sugars in the stalks as well as the seeds/grain of whatever grasses it is cut from. It is used to feed livestock year round and is the primary feed in winter. It is often supplemented by grain or feed.

Straw is basically an industrial byproduct and is the leftover stalk from grain harvesting. Usually produced from wheat after harvest. Used as bedding.