Preserving feed for livestock doesn't always mean putting up sun-dried hay. Silage is also made as a chopped, fermented feed source, primarily from annual crops like corn, barley, sorghum, oats, millet, and occasionally canola and wheat. Silage is made by packing the chopped crop into a "pit" and packing it down well so that any oxygen pockets are eliminated. Oxygen pockets encourage spoilage of the feed. Silage and haylage can be interchangeable, especially since haylage or baleage involves the same process of ensiling to preserve feed for livestock. However, silage more relates to annual crops than perennial forages. How to make silage is described in the steps below.