McDonald’s Chicken Goes Antibiotic-Free. Now What?

Fast-food giant McDonald’s shook up the food world last week by announcing that within two years, it will require all 14,000 of its U.S. restaurants to serve chicken that is substantially antibiotic-free. It’s a huge change, because so much of poultry raising has relied on drugs for so long. What will it mean?

The announcement is important news, further evidence of the way that consumer demand has been pushing the food industry toward meat raised without antibiotic use. Customer pressure has achieved results far faster than policy attempts to change meat production, which have been mired in political in-fighting since the 1970s. The announcement puts McDonald’s in line with smaller restaurant chains such as Chipotle, Panera and Chick-fil-A, which have all committed to meat raised without routine antibiotic use—but because McDonald’s is so much bigger, the decision is likely to influence the rest of the market for meat in a way those other companies have not.

There was one significant footnote to the McDonald’s announcement, and it left a fair number of people scratching their heads. The company said that it would exclude the use of “medically important” antibiotics, but continue to use one class of drugs, called ionophores.

So what does “medically important” mean? And what is an ionophore?

Here’s a quick lesson in agricultural antibiotics. There are two main things to know: how drugs are used, and which drugs they are. First, let’s look at how. Antibiotic use in livestock is a spectrum. On one end, there is giving chickens, cattle and hogs doses that cure diseases, just as we do for humans. On the other end, there is “growth promotion” (sometimes called “feed efficiency”), a practice that dates to the 1950s, which gives tiny doses — much smaller than treatment doses — to make animals put on edible muscle more quickly. In between, there is a middle category called prophylaxis or sometimes metaphylaxis, in which medium-sized doses of drugs are given to animals to prevent them from contracting illnesses they are exposed to.

Next, let’s look at what. Here’s a table from a report published by the Food and Drug Administration, the Summary Report on Antimicrobials Sold or Distributed for Use in Food-Producing Animals, which is the U.S. government’s sole accounting of what drugs and drug families are used in livestock. (The original of the report, including the footnotes to this table, is here.)

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The FDA’s most recent (2012) accounting of antibiotic use in US livestock. Original here.

If you read down the “Drug Class” column, you’ll spot names that might sound familiar from your own medical experience: tetracyclines (the most-used drug in animals), penicillins and sulfa drugs, for instance. That’s because many of the drugs used in livestock are functionally identical or closely related to ones used in humans. And that’s important because, if the drugs’ use on the farm causes antibiotic resistance to  emerge, infections that occur in  humans from those resistant bacteria will not respond to the drugs needed to cure them.

That possibility—that on-farm use causes untreatable, off-farm resistance—is at the heart of policy concerns over farm antibiotic use. It has caused the World Health Organization and the FDA to counsel “judicious use” of antibiotics, including asking agriculture specifically to cut back on using antibiotics that are also used in humans. It’s also the motive behind the Preservation of Antibiotics for Medical Treatment Act (PAMTA), a bill introduced numerous times by Rep. Louise Slaughter (D-NY), a public health microbiologist, which would forbid agriculture from using drugs that are important in human medicine.

And those moves are why McDonald’s feels ionophores are OK. Those drugs—which in chickens go primarily to control a parasitic disease called coccidiosis—are only used in animals, not in humans. (Here’s a pretty technical scientific article on them.) Therefore, there’s no concern over resistance to the drug arising; since ionophores are never used in humans, that an infection might not respond to ionophores isn’t a concern. That view is shared not just by the FDA, which is in the midst of a three-year attempt to control farm antibiotic use but allows ionophores under that control program, but also by the European Union, which has passed strict antibiotic-control policies but gave ionophores an exception.

Ionophores get a pass as well from many public health advocates. “If you use that antibiotic, instead of the antibiotics that are used in human medicine, it really does help preserve those medically important antibiotics,” Dr. Gail Hansen, a veterinarian with the Pew Charitable Trusts, tells The Plate.

An important issue for some of the other farm antibiotics is what is called “cross-resistance”—that is, when bacteria construct defenses against the attack of a drug, those defenses may allow them to resist other drugs that  they never were exposed to. There is no clear evidence yet—possibly because no one bothered to look—whether ionophores provoke resistance that might affect the action of other more important drugs. One lab study done in 2003 (using an ionophore that is given to cattle, not to poultry) found that the drugs’ use stimulated resistance to one other antibiotic, bacitracin—which in the United States is used in people only as an ingredient in first-aid creams.

So for the problem of provoking antibiotic resistance, the ionophores might be in the clear. For some advocates, though, what is most important is that ionophores are still antibiotics—and thus, strictly speaking, their use perpetuates farming practices that can rely on the drugs to prop up unhealthy birds or bad hygiene. For them, this move doesn’t go far enough, because in their view it allows the persistence of a system that values productivity over animal welfare. But given the decades-long battle over agriculture’s antibiotic use, there’s no question it is an important step.