This is the VOA Special English Agriculture Report.

Antibiotics are used to cure bacterial infections. But about fifty years ago, farmers started to give small amounts of these drugs to healthy animals in their feed. Scientists found that antibiotics improve the growth rate of animals.

But the practice soon led to criticism. Public health experts observed antibiotic-resistant bacteria growing in these animals. Experts say bacteria develop resistance from continual exposure to antibiotics. And resistant bacteria can make it harder to treat infections in humans.

Today big livestock producers around the world use antibiotics for animal growth. Some countries are considering restrictions or already have them. South Korea is banning the practice in July. The European Union began to enforce a ban five years ago. Several EU members had already stopped the practice before that.

In the United States, the Food and Drug Administration first proposed to ban antibiotic use in healthy animals in nineteen seventy-seven. Congress, however, asked for more research. Today there is no ban. But in June of last year the FDA asked producers to stop the practice over time.

That recommendation was not enough for some critics. Five environmental and consumer groups are asking a court to force a ban by the federal agency. Steve Roach is with the group Food Animal Concerns Trust, or FACT.

STEVE ROACH: "As far as we can tell, all they were trying to do was kindly ask the industry to make changes. And we just do not believe that is [an] adequate response."

His group wants the government to ban the use of two common antibiotics at levels below those used to treat sick animals.

STEVE ROACH: "After thirty years, I think it is time for someone to put a little more pressure on them. And that is what the aim of the lawsuit is."

Supporters of low-level antibiotic use in animals say there is no solid evidence linking it to drug-resistant infections in humans. They also say that in addition to increasing growth, the drugs help suppress diseases in animals confined together in large feeding operations.

Ron Phillips is with the Animal Health Institute, a trade group for the animal-drug industry. He says suppressing animal disease means a safer food supply.

RON PHILLIPS: "Sicker animals result in greater contamination on the meat. So the way to control pathogens on the farm, so that they do not transfer through the food chain, is to make sure we have healthy farm animals."

Experts say the largest source of resistant bacteria is the overuse and misuse of antibiotics among people.