They acknowledge that antibiotic-free animals can be raised by small, organic farms but say large-scale meat production requires antibiotics to keep animals healthy.

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"We're pretty darn committed to our cattle, and our goal is to not have them get sick," said Mike Apley, a cattle farmer and professor of veterinary medicine at Kansas State University.

Farmers like Apley also point to a handful of studies that conclude the risk to humans is extremely low.

One 2004 estimate conducted by scientists consulting for the meat industry, for instance, placed the likelihood that antibiotic would not work in a human due to animal use at 1 in 82 million.

And, they argue, it's the overuse of antibiotics in humans - not animals - that's causing a rise in drug-resistant bacteria. Indeed, for decades, doctors have prescribed antibiotics for common ailments like the flu and sinus infections that are not caused by bacteria.

Studies show doctors often feel pressured to prescribe the drugs.

"The problem is not an animal or human issue per se," said Dr. Tom Chiller, associate director for epidemiologic science at the Centers for Disease Control and Prevention. "It's about using the antibiotics as judiciously as we possibly can in situations where they are needed."

Some Americans are becoming more aware of the issue. Liza Greenfield, 33, said she will only buy organic, antibiotic-free meat at farmers markets because she doesn't think animals should be given antibiotics for growth.

"A cow is supposed to eat grass," said Greenfield, an administrator at the New York University. "I want to know it was out on the pasture eating grass."

As Americans show more interest, so are companies. Some of the largest restaurant and grocery chains including Kroger and Safeway now offer antibiotic-free meat.

And last month, executives from companies such as Chipotle Mexican Grill and Bon Appetit food services that offer antibiotic-free meat and poultry gathered in Washington to lobby for restrictions on the use of antibiotics in animals.

The FDA last week said it would ask drugmakers to voluntarily stop marketing antibiotics for non-medical uses on their labels with a goal of completely stopping the practice in a few years.

Animal drugs can only be legally prescribed for uses listed on the label, so the change is expected to have a major impact on how farmers use them.

Some public safety advocates complained that the FDA, which worked with drugmakers on the proposal, should have mandated the change. But the FDA said a formal ban would have required individual hearings for each drug, which could have taken decades.

"We think the science is very solid in showing that largely indiscriminate use of antibiotics contributes to resistance," said FDA Deputy Commissioner MichaeI Taylor. "I don't think there's really any question about it."