"Meaningful change is unlikely in the future," concluded the 14-member panel, assembled by Johns Hopkins University, in a report released on Tuesday that quickly drew protests from livestock industry groups.
The release marked the fifth anniversary of a landmark 2008 Pew Charitable Trust report that called for an end to the sub-therapeutic use of antibiotics by livestock producers, as well as an end to practices such as tiny cages for laying hens.
Congressional hearings followed the release of that report, and the livestock industry went into damage control mode.
The Johns Hopkins' report said "additional scientific evidence has strengthened the case that these (non-therapeutic) uses pose unnecessary and unreasonable public health risks" of allowing bacteria to develop resistance to antibiotics.
"We have even better science to support the recommendations we have made," said Mary Wilson, an epidemiologist at Harvard University. "We are, in fact, running out of antibiotics. We are seeing infections that are untreatable."
More than 2 million Americans are sickened by antibiotic-resistant infections each year and 23,000 of them die, according to the U.S. Centers for Disease Control And Prevention.
Livestock industry leaders said the new report was a scare-mongering attack that did not provide a clear link between antibiotic use in livestock and the rise of antibiotic-resistant illness in humans.
Critics of antibiotic use are "just pushing a pre-set agenda," said Scott Hurd, an associate professor at Iowa State University who works on risk assessment.
Different antibiotics are prescribed for people than those used on livestock, industry groups noted. They tied drug-resistant bacteria strains to over-use of antibiotics by people.
Antibiotics are routinely sprinkled into U.S. cattle, hog and poultry feed to promote growth and are also used to prevent and treat illness. Agriculture accounts for 80 percent of antibiotic sales, according to the limited records available.
Robert Lawrence, director of the Johns Hopkins Center for a Livable Future, which produced the report, blamed "the political power of industrial agriculture" for lack of action on antibiotics and other reforms.
Legislation to expand the U.S. Food and Drug Administration's power over antibiotics use in livestock has stalled repeatedly in Congress.
"Antibiotics were invented to cure sick humans, not to compensate for unsanitary conditions on the farm or fatten animals up so they could sell for more at the market," said Rep. Louise Slaughter, a New York Democrat.
Former Kansas Governor John Carlin, who chaired the review for Johns Hopkins, said growing public interest in food production eventually will outweigh today's anti-government mood, and "I would say to my friends in production agriculture the next few years would be a good time to cut some deals."
James Merchant, the former dean of public health at the University of Iowa, said research on antibiotic resistance was "getting much stronger and more specific." As well, he said, the incidence of antibiotic resistance declined in countries, such as Denmark, that restrict antibiotic use in livestock.
In one study in Pennsylvania, researchers said people have a greater chance of one type of antibiotic-resistant infection if they merely lived near fields fertilized with hog manure or high-density hog farms. The study was published on September 16 in the journal JAMA Internal Medicine.
A 2012 study published in a journal of the American Society for Microbiology concluded that the routine use of antibiotics by cattle feed lots may facilitate the emergence of antibiotic-resistant pathogens.
While the FDA has altered its guidelines to say antibiotics should be used only under the guidance of a veterinarian for prevention, control or treatment of disease, the Johns Hopkins report said there was a loophole. Drugmakers can ask for FDA approval of their products for disease prevention at the same dosages as when they were used to speed animal growth.
"This means that while antimicrobial approvals may change ... antimicrobial use may not," said the report.
Richard Raymond, a former agriculture undersecretary for food safety, said in a report for the Animal Agriculture Alliance, a livestock group, that antibiotics are part of an array of biological tools for livestock producers.
Among them are beta-agonists, a type of feed additive that helps animals gain weight more quickly, and man-made bovine hormones used to boost dairy production.
U.S. drugmaker Merck & Co. suspended U.S. and Canadian sales of Zilmax, the leading beta-agonist, on August 16 following concerns about cattle that appeared to be sore-footed or were having difficulty walking after being fed the additive.
