Most of the turkey growers that Minnesota veterinarian Jill Nezworski works with mix antibiotics into their birds' feed only to cope with disease -- quelling a cough outbreak or easing a bout of avian diarrhea.

A minority, however, also use the drugs to boost their birds' growth and improve the conversion of feed into body mass. Some hog farmers, cattle ranchers and chicken producers do the same sort of thing.

But decades of concern over the effects of animal antibiotic use on the health of the humans at the end of the food chain have boiled to the point where federal regulations are in the works that could curb their use. The U.S. Food and Drug Administration is on the verge of releasing new guidelines on animal antibiotics to limit their application to animal health.

The stakes are high in Minnesota, a national leader in turkey and hog production, and where antibiotic use is common on the farm.

"You can clearly say that in the next couple of years there will be an impact on the availability of antibiotics [for animals]," said Jeff Bender, director of the University of Minnesota's Center for Animal Health and Food Safety. "Change is coming, and the change will be less antibiotic use in feed."

Meanwhile, a federal judge on March 22 ordered the FDA to begin hearings -- originally proposed in 1977 -- on the safety of two popular antibiotics. The drugs could be banned for animal use if found to imperil human health. How the judge's ruling might affect the FDA's new guidelines isn't clear. Nor is the exact extent of any antibiotic limitations from the FDA or how they would be policed.

The FDA's proposed guidelines, which will be voluntary, are "a good first step," said Gail Hansen, a veterinarian and senior officer at the Pew Charitable Trusts, which is campaigning for animal antibiotic limits. "But they should not be seen as a 'dust-our-hands-off-and-we're-done' solution."

Over time, people have become more resistant to antibiotic drugs, posing a public health issue. It's a phenomenon driven by many factors, and the role of animal antibiotic use is a matter of debate. But according to a 2010 FDA report, numerous studies indicate that use of antibiotics in food-producing animals is linked to antibiotic resistance in humans.

Essential tool in Minnesota

Antibiotic drugs have been used on livestock for decades. They're an essential "tool in the toolbox" of any veterinarian, said Nezworski, a Buffalo Lake veterinarian who works with turkey and chicken growers in Minnesota and the Dakotas.

Minnesota is the nation's largest turkey-producing and processing state, with 250 farmers raising more than 49 million birds annually. Veterinarians like Nezworski use antibiotics to battle conditions like "ort," a respiratory infection, or nasty bugs like E. coli, a primary killer of turkeys.

With increasing consumer demand for free-range turkeys, a whole new disease front has opened up, Nezworski said. Free-range birds are exposed to soil bacteria, and that means exposure to new pathogens, thus requiring antibiotic use.

Nezworski said 10 percent to 15 percent of her clients give birds lower doses of antibiotics for what's known as "sub-therapeutic" purposes: To help boost growth and increase feeding efficiency, the latter giving growers more bang -- in terms of bird muscle mass -- for their feed buck.

The livestock industry and antibiotic-reduction advocates have come up with differing tallies of how often antibiotics are used for subtherapeutic purposes, the U's Bender said. But reliable, neutral information is scarce, he said.

Livestock industry officials say subtherapeutic use is declining and is done by a minority of farmers. "It's a thing of the past where every farm is using [antibiotics] all the time," said Dave Preisler, executive director of the Minnesota Pork Producers Association. Minnesota is the nation's third-biggest hog producing state.

Antibiotic use varies from farm to farm, and "the end goal, if you can, is to use nothing," Preisler said.

Nezworski, the veterinarian, noted that antibiotics are expensive, "so you don't want to waste them. The big picture is that they are not used willy-nilly."

Most of the antibiotics administered in the United States go into animals, not people. And concern that animal antibiotic use could ultimately be affecting human health goes back decades.

FDA finishing what it starts

As far back as 1977, the FDA was concerned enough to call for hearings on banning animal application of penicillin and tetracycline, two common antibiotics. The FDA never held those hearings, formally abandoning them late last year and focusing on its proposed voluntary guidelines.

But a ruling by Judge Theodore Katz in New York last month called for the FDA to hold the hearings. "The judge's decision was based on the idea, 'You need to continue what you started in 1977,'" said the U's Bender.

An FDA spokeswoman, asked whether the agency plans an appeal or whether the court ruling will affect its final guidelines, said in an e-mail, "We are studying the opinion and determining our next steps."

Hansen of the Pew Charitable Trusts said the FDA guidelines are still expected, regardless of the court decision.

The FDA's draft guidelines call for antibiotics in animals to be used "as judiciously as possible." The drugs "should be limited to those uses that are considered necessary for assuring animal health," the draft report said.

That would include not just treatment of disease but also prevention, which Bender called a "gray area."

Antibiotic-reduction advocates such as Hansen are wary that for some farmers, drug use for disease prevention would be a cloak for boosting animal growth.

The FDA appears to acknowledge such issues, noting in its draft guidelines the concerns that preventive use of antibiotics is not "appropriate or judicious." However, the draft guidelines say some preventive use is necessary.

Hansen and other antibiotic-reduction advocates are also concerned about the voluntary nature of the FDA's solution. The FDA has established no mechanism for even tracking compliance, she said.

Livestock industry officials, however, say that while voluntary, the guidelines are coming from a primary federal regulator, so there will be pressure to comply.

Nezworski, the turkey doctor, said she just wants to be sure she still has the drugs she needs to improve bird health. "I sure hope a little common sense prevails."

Mike Hughlett • 612-673-7003