The use of antibiotics in animals raised as food is being phased out, federal health officials announced Wednesday, in a major decision that marks a significant shift in factory-farming and its impact on human health.

The U.S. Food and Drug Administration is calling on the pharmaceutical industry to voluntarily relabel a vast roster of antibiotics and restrict their use in food-animal production. These medications, which are widely used to treat human and veterinary infections, are to be phased out of animal farming over the next three years.

Factory-farmed animals are those raised for their meat. For decades, antibiotics have been added to feed and/or drinking water for pure economic reasons, such as artificially forcing animals to pack on more weight, which ultimately drives up profits once they are butchered and sold.

If pharmaceutical manufacturers comply with relabeling, it would become illegal for animal farmers to buy the medications to fatten flocks and herds.

FDA officials Wednesday said the key reason for implementing the new policy is to stop producers of food animals from using antibiotics to spur rapid growth.

"Implementing this strategy is an important step forward in addressing antimicrobial resistance," FDA Deputy Commissioner for Foods and Veterinary Medicine Michael Taylor said in a statement yesterday.

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Several dynamic consequences occur as a direct result of overdosing animals with antimicrobial medications, experts say. One is the formation of multidrug resistant bacteria, which are easily passed to humans.

Another equally frightening consequence is the number of antibiotics that become impotent against major human and veterinary infections because the drugs have been overused for economic purposes in agriculture.

"The action by the FDA makes sense from numerous theoretical points of view as well as many practical ones," said Dr. Aaron Glatt, executive vice president and chief administrative officer of Mercy Medical Center in Rockville Centre.

"The more that antibiotics are around in the environment, there are bacteria that will develop resistance to them, and as a result, the antibiotics become less effective when used in humans," added Glatt, a specialist in infectious diseases.

One dangerous offshoot of antibiotic overuse in agriculture, according to a study last year, is the estimated tenfold increase in multidrug-resistant salmonella on chicken breasts, the most widely consumed meat product in the country.

Currently, about 80 percent of all antibiotics sold by pharmaceutical companies in the United States go to animals processed as food, which amounts to an estimated 30 million pounds of the drugs being consumed by factory farmed chickens, cows, pigs and sheep.

People directly consume only a fraction of the antibiotics sold yet are amid one of the biggest antibiotic resistance crises since the drugs were first commercialized after World War II.

Many critics of widespread antibiotic use in factory farmed animals blame the crisis on indiscriminate agricultural use.

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Glatt as well as federal infectious disease experts say the country is on the precipice of a post-antibiotic era, which means few, if any of the drugs will be able to treat major infections in the not-too-distant future, unless a dramatic change reverses how the drugs are used now.Jean Halloran, director of food policy at Consumers Union in Yonkers, applauded the agency's new policy, but said it's still not enough.

"It's a good first step down the path towards ending antibiotic overuse in animal agriculture and more than any administration has done in 37 years, but much more needs to be done," she said.