Beef cattle stand in a barn on the Larson Farms feedlot in Maple Park, Ill. Daniel Acker/Landov hide caption

itoggle caption Daniel Acker/Landov

Craig Rowles tends to his pigs in a barn near Carroll, Iowa. Dan Charles/NPR hide caption

itoggle caption Dan Charles/NPR

A truckload of live turkeys arrives at a Cargill plant in Springdale, Ark., in 2011. Most turkeys in the U.S. are regularly given low doses of antibiotics. Danny Johnston/AP hide caption

itoggle caption Danny Johnston/AP