What is the use of field corn?

There are two categories that corn grown in the US is generally placed into. "Sweet" corn and "field" corn. The sweet variety is what you are used to eating. The field variety is used to feed animals, make alcohol, and in some commercially processed foods like breakfast cereals.

When distilling alcohol from corn the starches are used. If the remaining "distiller's grain" byproduct is fed to beef there is no loss in nutritional value. Cattle have a rumen, which removes the starch as waste anyway.