Black Angus cattle stand in a pen before being auctioned off at the Muskingum County Livestock Auction in Zanesville, Ohio. (Ty Wright/Bloomberg News)

The Food and Drug Administration took steps Wednesday to try to phase out the use of certain antibiotics in livestock and ensure that drugs given to animals on factory farms are prescribed by veterinarians to prevent and treat diseases, rather than merely to boost growth.

The agency finalized recommendations asking animal drug manufacturers to voluntarily alter their labels so that farmers would no longer be allowed to use antibiotics merely to make animals grow faster. In addition, the agency wants to curb over-the-counter sales of antibiotics and require farmers to get approval from a veterinarian before administering the drugs to livestock.

The announcement, welcomed by representatives of the agricultural industry but panned by some consumer advocates who had hoped for more aggressive action, comes amid growing concern that the widespread use of antibiotics in animals is helping to create resistant “superbugs” that sicken and kill thousands of Americans each year.

The vast majority of antibiotics sold each year in the United States — by some estimates as much as 80 percent — are used in agriculture rather than in human medicine. For years, consumer and environmental groups have hounded Congress and the FDA to regulate more stringently the amount of antibiotics given to animals, but the government has done little to forcibly limit the practice.

Michael Taylor, the FDA’s top food safety official, said the agency’s action will create significant and meaningful changes to the agriculture industry’s status quo.

“There will be fewer approved uses, and the remaining uses will be under tighter control,” Taylor told reporters Wednesday, adding that agency officials decided to make the new recommendations voluntary because they believed it would offer the quickest and most efficient route to altering current practices. “It avoids legalistic, product-by-product regulatory proceedings that would take years to complete.”

Companies will have 90 days to say whether they plan to sign on, followed by three years to implement the changes. FDA officials on Wednesday said some of the biggest animal-drug producers have already backed the agency’s plan, and Taylor said he remained confident that more companies soon would follow suit.

Public health activists and consumer advocates, who have raised alarms in recent years about the potential consequences of the overuse of antibiotics in animals, praised the FDA for trying to address the decades-old problem of antimicrobial resistance. But they also argued that the agency’s efforts lack teeth, and that companies too easily will be able to ignore or circumvent the new standards. They also said they worried that the policy would allow companies to continue to use the drugs to compensate for cramped and unsanitary living conditions that can foster disease in animals.

Rep. Louise M. Slaughter (D-N.Y.), a microbiologist who has unsuccessfully tried to pass legislation limiting the use of certain antibiotics to humans and sick animals, called the agency’s efforts “an inadequate response” that “falls woefully short of what is needed to address a public health crisis.”

Avinash Kar, a health attorney for the Natural Resources Defense Council, called the policy “an early holiday gift to industry.”

“It is a hollow gesture that does little to tackle a widely recognized threat to human health,” Kar said in a statement. “FDA has essentially followed a voluntary approach for more than 35 years, but use of these drugs to raise animals has increased.”

Taylor said he understands the strong opinions surrounding the issue and the lingering skepticism about voluntary regulations.

“There are a lot of reasons why companies have an incentive to take this action,” Taylor said. He added, “We reserve our ability to take regulatory action.”

In a call Wednesday afternoon, representatives from industry lobbying groups such as the Animal Health Institute and the National Pork Producers Council reiterated their support of the FDA’s new policies, which the agency first proposed last year.

“It’s going to mean a real change for how antibiotics are used on the farm,” said Liz Wagstrom, chief veterinarian for the NPPC.

Richard Carnevale, AHI’s vice president for regulatory, scientific and international affairs, said that even though the new recommendations are voluntary, it makes little sense for companies to try to ignore or avoid them. “They risk the goodwill of their customers, and they risk the potential wrath of the FDA,” he said.

Although the problem of antimicrobial resistance has been acknowledged for decades, the overuse of antibiotics in animals has taken on a higher public profile in recent years, as health officials and consumer groups have issued more and more dire warnings about the potential consequences.

In September, the Centers for Disease Control and Prevention issued an alarming report about the growing threat of antibiotic-resistant infections, which kill an estimated 23,000 Americans each year. While most of those infections arise in hospitals and nursing home settings, officials underscored the massive use of antibiotics in animals as a serious concern.

“Resistant bacteria can contaminate the foods that come from those animals, and people who consume these foods can develop antibiotic-resistant infections,” the CDC’s report stated. “The use of antibiotics for promoting growth is not necessary, and the practice should be phased out.”

In October, a separate report from the Johns Hopkins Center for a Livable Future found that pharmaceutical and farm lobbies had successfully blocked legislative reforms to the widespread use of antibiotics in U.S. livestock, and the organization said regulation had grown only weaker under the Obama administration.

Those findings came five years after a detailed report from a Pew Charitable Trust commission, which found that the constant feeding of antibiotics to animals in order to plump them up and ward off potential disease was making those drugs less and less effective and the bacteria they were meant to treat ever-more resistant to medicines.