The most wholesome label to look for is organic, this quarantees there were no antibiotics administered to the animal or poultry. Companies who sport this label are required to pass inspection once each year. A label that says no antibiotics administered do provide documents to the USDA but no inspection takes place and natural does not refer at all to how animals or poultry are raised. The Preservation of Antibiotics for Medical Treatment Act will help to preserve the effectiveness of antibiotics by reducing the frequency they are used, so be sure to enlist your members of congress to support this act.
 

http://www.ucsusa.org/food_and_environment/sustainable_food/green-cuisine/issue2-fall-2007/green-cuisine.html