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

itoggle caption Paul Sakuma/AP

An order of McDonald's Chicken McNuggets in Olmsted Falls, Ohio. McDonald's says it plans to start using chicken raised without antibiotics important to human medicine. Mark Duncan/AP hide caption

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Chicks in the Perdue hatchery in Salisbury, Md. The company says an increasing number of its chickens are now raised using "no antibiotics, ever." Dan Charles/NPR hide caption

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Young broilers nibble feed at a chicken farm in Luling, Texas. The Food and Drug Administration has issued new guidance on how drug companies label antibiotics for livestock. Bob Nichols/USDA/Flickr hide caption

itoggle caption Bob Nichols/USDA/Flickr

Turkeys sit in a barn in Sonoma, Calif. An estimated 46 million turkeys are cooked and eaten during Thanksgiving meals in the U.S. Justin Sullivan/Getty Images hide caption

itoggle caption Justin Sullivan/Getty Images

In recent years, pork producers have found ways to keep the animals healthy through improved hygiene. M. Spencer Green/AP hide caption

itoggle caption M. Spencer Green/AP

Cattle crowd inside a feedlot operated by JBS Five Rivers Colorado Beef in Wiley, Colo. John Moore/Getty Images hide caption

itoggle caption John Moore/Getty Images

Piglets in a pen on a hog farm in Frankenstein, Mo. Jeff Roberson/AP hide caption

itoggle caption Jeff Roberson/AP

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