But the impact of McDonald's action on the U.S. beef, pork, and poultry industries may be minimal because many producers either no longer use these antibiotics or have alternative treatments, industry sources said.

McDonald's policy comes amid heightened consumer awareness of the use of additives in food production, including a backlash against genetically modified crops.

McDonald's, the world's largest fast-food chain, uses more than 2.5 billion pounds of chicken, beef and pork annually.

Health and consumer organizations for years have been concerned that using certain antibiotics in meat-producing animals could lead to antibiotic-resistant germs in humans.

McDonald's said its new policy calls for the elimination of antibiotic drugs some producers have used to help animals grow faster. It sets standards for its direct suppliers and encourages indirect suppliers to take similar steps.

"The fact that McDonald's publicly stated this, even though to a large extent much of the food industry had already been taking a good, hard look at whether the use of antibiotics in animals is really warranted, puts a big stamp of approval on many of us who have championed the cause to remove antibiotics as growth promoters," said author Stuart Levy.

Levy wrote the 2002 book "The Antibiotic Paradox: How the Misuse of Antibiotics Destroys Their Curative Powers," and is a professor of medicine and microbiology at Tufts University.

"We take seriously our obligation to understand the emerging science of antibiotic resistance," McDonald's, based in Oak Brook, Illinois, said in a statement.

Two major U.S. meat producers that supply McDonald's, Tyson Foods Inc. and privately held agribusiness conglomerate Cargill Inc., were part of a coalition that created the policy, McDonald's said.

In 2000, McDonald's Europe began phasing out growth-promoting antibiotics, and by the end of 2001 all European-based poultry suppliers had eliminated such use in chicken feed.

The U.S. beef and pork industries have largely abandoned the use of growth-promoting antibiotics, industry sources said.

"They do use antibiotics in cattle and hogs, but it is more for treatment (of ailments)," said Terry Franc, chief economist for the American Farm Bureau (news - web sites) Federation, the nation's largest farm organization.

The National Cattlemen's Beef Association (news - web sites) said antibiotic growth promoters are of little use for cattle.

But it said antibiotics approved by the U.S. Food and Drug Administration (news - web sites) have been tested and pose no threat to animal or human health, and it criticized McDonald's policy for being inconsistent with FDA's "science-based" rules to assure safe food.

Richard Lobb, spokesman for the National Chicken Council, said the poultry industry uses antibiotics for treating animal ailments, but alternative medicines are available.

"The use of antibiotics in general has been declining in poultry for a long time," he said.

McDonald's said its antibiotics policy for food animals was developed with the help of Environmental Defense, an environmental advocacy organization, and Elanco Animal Health, an animal pharmaceutical company.

(Additional reporting by Matthew Lewis and Peter Bohan in Chicago).