Big news in the world of food policy, farming and antibiotic use: Perdue Farms, the third-largest chicken producer in the United States, announced today that during the past decade it has ceased using most of the antibiotics that formerly propped up its chicken production.

There are caveats to that "most," and I'll explain them. But it's important to say up front that this is a nationally significant move and looks like an industry-leading step.

Here are the details: In a statement, and in a press conference held in Washington, DC, the poultry company said that it has ceased:

using any antibiotics for growth promotion or for disease prevention;

using antibiotics that are important in human medicine in 95 percent of its birds;

injecting meat chickens with antibiotics while still in the shell.

Those restrictions mean the company has eliminated most of the uses of antibiotics that public health campaigners have been concerned about since the 1970s, and has gone beyond current federal requirements for what can be done to meat chickens before they hatch. And while the impact probably can't be measured with precision as long as other firms continue to use antibiotics routinely, it seems likely that Perdue has taken an important step in reducing the amount of antibiotic resistance that comes off farms and causes human illness.

The company said it began its antibiotic reduction program 12 years ago. The trigger for today's announcement was completing the removal of antibiotic use from its hatcheries, which was a five-year project that ended this summer.

"When we started hearing from consumers that they were becoming concerned about the amount of antibiotics used to raise chickens they were buying, we were listening," company chairman Jim Perdue said at the DC briefing. "Coupled with information coming from the USDA and FDA and other sources, we began to look critically at our practices. It wasn't easy...but we found along the way that we could raise healthy chickens with fewer antibiotics."

Routine antibiotic use in meat production – that is, giving meat animals small doses of antibiotics every day in food or water, to make them put on weight faster and to prevent disease from the conditions they live in – has been under scrutiny for decades. The first federal action addressing it happened just last December, when the FDA asked veterinary pharmaceutical manufacturers to relabel the antibiotics they make, so that "growth promotion" – that weight-gain use – would become an unapproved, technically illegal use of the drug.

The concern that lies behind routine animal antibiotic use is that most of the drugs used on farms are the same ones used against infections that humans develop. Bacteria in animals' guts or on their skin develop resistance to protect themselves; when the animals are slaughtered, or their manure washes or wafts off the farm property, the resistant bacteria go along too. When humans pick up those bacteria from meat or the environment, they can't be treated – because the drug needed to cure them is the same one that was used on the farm in the first place.

The one exception to that concern is a category of antibiotics called ionophores. They are only used in animal medicine and not approved for humans. So while they promote the emergence of resistance – all antibiotics do – they don't take a human treatment out of the medical artillery. (Nationally, according to FDA data, 4.12 million kilos of ionophores were sold for animal use in 2011, the last year for which data has been published. That comes out to 30 percent of the 13.5 million kilos of antibiotics sold for animal use that year overall.)

The "ionophore exception" is why the Perdue announcement and release today included words like "fewer" from Perdue himself, and statements like this from Dr. Bruce Stewart-Brown, Senior Vice President of Food Safety, Quality and Live Operations: “By no longer using any antibiotics in our hatcheries or any human antibiotics in feed, we’ve reached the point where 95 percent of our chickens never receive any human antibiotics, and the remainder receive them only for a few days when prescribed by a veterinarian."

Stewart-Brown said during the briefing that the company's ionophore use is also trending down, but wasn't willing to give figures. The only birds to receive the ionophores, he said, are the company's regular brand of chicken; neither the organic nor the "no antibiotics ever" lines do. However, he said, animals that get sick will be treated with antibiotics if the company's veterinarians think it is needed, but then will be sold under the regular brand.

To compensate for the lost effect of the antibiotics the company relinquished, Stewart-Brown said they also improved chickens' diets by removing animal byproducts and going to an all-vegetable feed of soybean meal and corn oil; using prebiotics and probiotics including "oregano and yucca" and "yogurt type things"; increasing the number of vaccinations chickens receive; and doubling down on cleaning chicken "houses," the long sheds that can hold tens of thousands of broilers at a time.

"This doesn't mean we are done," he said. "We constantly learn new things and try to evolve our program."

Campaigners for reduced antibiotic use mostly supported the comprehensive moves.

Gail Hansen, a public health veterinarian with the Pew Charitable Trusts, told me: "This is a lot of what we have been asking for, for six years, so it is pretty positive," adding that she would like to see the company be more specific about the amounts of ionophores it uses and about better husbandry practices that could help boost broiler chickens' immune systems.

Caroline Smith DeWaal, food safety director at the Center for Science in the Public Interest, said: "The amount of antibiotics used on the farm is simply not sustainable if we want to preserve their uses in human medicine. I hope Perdue's actions foreshadow changes across the industry, and embolden regulators to prohibit the misuse of antibiotics in animal agriculture."

Paige Tomaselli, senior attorney at the Center for Food Safety, said: “We appreciate Perdue’s initiative, but they produce only 7 percent of the broilers produced in the U.S. Other companies should follow suit.”

Jonathan Kaplan, Natural Resources Defense Council: "Jim Perdue [says]: '… human-approved antibiotics should not be used to boost production or in place of responsible animal husbandry or hatchery management.' We agree!... We’d like to hear more about how Perdue is verifying these accomplishments and hope the company will also publish its actual antibiotic use data."

Susan Vaughn Grooters of Keep Antibiotics Working praised the moves but raised a concern about birds that are outside Perdue's system but feed into it: the great-grandparent and grandparent birds that maintain the lines Perdue uses to create its broilers' parents.

"Reducing antibiotics use is laudable, but we won't fully address threats to human health until we're looking at the whole poultry production system, including breeders," she told me. "Purdue mentioned that they don't own the grandparent breeding flocks that supply to them. Consumers should be concerned with this black box. Through purchasing specifications and breeder production agreements, Purdue could further drive down antibiotic use in food animal production by addressing that use."

In a follow-up interview, Stewart-Brown said: "We are not in the genetics business, but one thing we are really clear on (with the breeding companies) is we believe it is very important they are breeding in such a way that the parents and the progeny from those parents are as hearty and capable. They understand, when we are buying their product, that we need birds that will be healthy enough not to need the help of antibiotics."

Homepage image: Peter Cooper/Flickr