Tyson Foods says it has already reduced its use of human-use antibiotics by 80 percent over the past four years. Here, Tyson frozen chicken on display at Piazza's market in Palo Alto, Calif., in 2010. Paul Sakuma/AP hide caption

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Chickens gather around a feeder in a Tyson Foods poultry house in Washington County, Ark. April L. Brown/AP hide caption

toggle caption April L. Brown/AP