Facing pressure from environmentalists and shareholder activists, major US food companies and restaurant chains are moving to limit antibiotics in farm animals raised for meat.
Last month, Tyson Foods announced a "no antibiotics ever" pledge for all Tyson-branded chicken products, building on an earlier promise to restrict drug use on broiler chickens.
Analysts see the latest Tyson announcement as further evidence of a trend of large companies limiting pharmaceuticals that scientists believe increases drug-resistance for treating pneumonia, infections and other illnesses in humans.
The wave started in 2014 with Perdue Chicken and chicken-based fast-food chain Chick-fil-A, followed by McDonald's, Wal-Mart Stores, Pilgrim's Pride and others. The announcements vary in scope, with some companies, for example, still permitting use of ionophores, antibiotics not used in human medicine.
The shift follows warnings about antibiotic resistance from health officials and a September 2016 United Nations General Assembly resolution that pledged coordinated action to address overuse.
"We're seeing a cry from consumers for meat that's responsibly raised," said Lena Brook, a food policy advocate for the Natural Resources Defense Council (NRDC).
Still, the breadth of the movement should not be overstated. While an estimated 40 to 50 percent of US chicken now is antibiotic-free, the percentage is far lower for pork and beef.
Moreover, several leading companies have resisted action. Kentucky Fried Chicken, part of Yum Brands, currently scores an "F" on an NRDC scorecard on antibiotics policy, while Sanderson Farms, a leading US chicken producer, has lampooned the trend.
"There's certainly strong and growing demand for it today, but to what extent it's a fad or a long-term trend remains to be seen," said Zain Akbari, a food industry analyst at Morningstar.
- Antibiotic-free premium -
Experts in animal farm science say US farmers for decades routinely employed antibiotics as a means to speed growth rates for animals, and to prevent disease outbreaks on farms where animals are frequently packed in close quarters.
But an April 2014 World Health Organization report warned of the potential for a "post-antibiotic era" in which "common infections and minor injuries can kill" as drugs become ineffective.
In voluntary guidelines that took effect in January, the US Food and Drug Administration said antibiotics in agriculture should be limited to medically necessary uses and not for weight gain.
The call by public officials has dovetailed with heightened consciousness about food in broader American society that has also propelled organic food.
Instead of antibiotics, Tyson is turning to probiotics and to botanicals such as oregano and thyme for routine treatment, while still employing antibiotics if birds become sick, a spokesman said.
Tyson, which has faced shareholder resolutions in recent years on its water policy and other sustainability issues, also plans to limit antibiotics in pork, beef and turkey, although it has not yet set target dates.
"We're eliminating human antibiotics because it's the most responsible approach to balance a global health concern and animal well-being," a Tyson spokesman told AFP.
"Antibiotics resistance is a very complex issue with no single cause and no single solution. It's a global concern and we want to be part of the solution."
As other companies have done, Tyson began with chicken, in part because chicken farms tend to be vertically organized within companies, compared with pork and beef, which involve contracts with outside farmers.
That means the company would need to institute programs that impact its suppliers, analysts say.
- Is beef next? -
Advocates of stricter antibiotic use are pressing for action on beef and pork too, and are preparing a shareholder resolution for McDonald's annual meeting.
Since beef already has more premium grades, adding antibiotic-free products could be another opportunity to introduce a pricier product, said Akbari, the Morningstar analyst.
Akbari said much of the current push is in response to millennials, who increasingly will "force retailers and producers to be pretty nimble."
Still, organic-minded millennials are not the only key segment in the vast US food market.
Sanderson Farms last summer unveiled a marketing blitz in which a pair of folksy, baseball-cap wearing consumers mock the antibiotic-free craze in television ads that question the scientific link of agriculture to the growth of drug resistance and the wisdom of paying more for antibiotic-free chicken.
Joe Sanderson, chief executive of the 62-year-old Mississippi company, defended the company's stance in a February 23 conference call.
"Everybody does not want that product," Sanderson said. "And everybody does not believe the claims on that product and nor is that claim important to everybody."