Shelbyville, Tenn., is an archetypal American working-class community of 16,000 people. Located 53 miles south of Nashville, it has one high school, one movie theater, six pawnbrokers and no parking meters. Its greatest claim to fame is the Tennessee Walking Horse, a smooth-gaited breed developed and tirelessly promoted locally. But far more visible are the 18-wheel tractor-trailers -- each loaded with roughly 5,000 chickens in open metal crates -- that rumble through town day and night. They're headed for the cavernous Tyson Foods plant on Shelbyville's west side, next to the Duck River. Tyson Foods Inc., based in Springdale, Ark., is the world's largest processor of chicken, beef and pork, with sales last year of $23.4 billion.