U.S. health officials say there is unequivocal evidence of a link between overuse of antibiotics in healthy livestock and drug-resistant disease in people.
In a break from previous policy, they are recommending an end to the practice.
In nearly all the major livestock-producing countries in the world, farmers add small amounts of antibiotics to the animals' feed. It keeps them healthy and helps them grow better.
Public health groups have opposed the practice because bacteria continually exposed to antibiotics will eventually develop resistance to them.
Antibiotic-resistant infections are one of the world's most serious health concerns. Many factors contribute to the rising incidence, including over-prescription of antibiotics by doctors and misuse among patients.
But routinely feeding the drugs to healthy livestock to improve growth is also contributing, public health groups say.
The livestock industry argues that it's a long way from farm to fork, and there's no evidence that feeding antibiotics to healthy animals is harming people.
Officials draw link
Ali Khan, a deputy director at the U.S. Centers for Disease Control and Prevention (CDC), disagreed at a recent congressional hearing in Washington, D.C.
"There's unequivocal evidence [of a] relationship between use of antibiotics in animals and transmission of antibiotic-resistant bacteria causing adverse effects in humans," he said.
Khan pointed to numerous scientific studies from Europe, Canada, and the United States, as well as reports from the World Health Organization and the U.S. Institute of Medicine, that all show a link between veterinary use of antibiotics and higher risk of drug-resistant infections among humans.
At the same hearing, Joshua Sharfstein, principal deputy commissioner at the U.S. Food and Drug Administration (FDA), said that, in one of the best studies researchers used molecular fingerprinting to follow an outbreak of drug-resistant bacteria: "You actually can trace the specific bacteria around and they find that the resistant strains in humans match the resistant strains in the animals."
These strong statements opposing the practice represent a new U.S. government position on the issue. The FDA recently issued new guidance to the livestock industry recommending they stop using antibiotics as growth promoters.
"This is a very important event," says Jorgen Schlundt, head of food safety at the World Health Organization. "And it's actually following the guidance that WHO already gave out where we suggested that countries should actually stop using antibiotics as growth promoters."
Until now, only the European Union has followed the WHO's suggestion, banning the practice in 2006. Schlundt says it remains common in other major livestock-producing countries.
Recommendation or regulation?
While the FDA's recommendations are seen as a step in the right direction, they are voluntary. Critics say that's not enough.
Schlundt says while countries vary in their appetite for regulation, "In our experience, regulation is probably needed in an area like this."
But others say more regulation would be a mistake. The livestock industry and the nation's leading veterinarians' group says the antibiotics are helping to prevent animal disease, which ultimately makes the food supply safer.
University of Minnesota epidemiology professor Randall Singer says a ban could do more harm than good.
"If we were to pull those antibiotics from disease prevention, we will see disease," he says. "And my fear is, as we see more disease, we'll end up with more problems in our food supply."
The CDC's Ali Khan and the FDA's Joshua Sharfstein said that fear is unfounded.
Congress is considering legislation that would ban certain antibiotics from animal use. But it faces strong opposition from farm-state lawmakers, and even its supporters say Congress is unlikely to pass the measure this year.