CHICAGO (Reuters) -Tyson Foods Inc will close two U.S. chicken plants with almost 1,700 employees on May 12, the company said on Tuesday. The closures show the biggest U.S. meat company by sales is still trying to figure out how to improve its chicken business that has struggled for years. Tyson will shut a plant in Glen Allen, Virginia, with 692 employees and a plant in Van Buren, Arkansas, with 969 employees, according to a statement.