A growing numbers of farmers and companies, stung by concerns increasingly raised by both the public and the medical community, are kicking the antibiotic drug habit.

It’s been a long time coming. Decades ago, scientists discovered that routinely feeding antibiotics to healthy livestock, including pigs, cattle and poultry, promoted slightly faster growth. And with the rise of modern industrial farming, antibiotics are now also used to compensate for stressful, crowded and often unsanitary living conditions for animals.

Four of the nation’s top 10 chicken producers – Tyson Foods, Perdue Farms, Gold Kist and Foster Farms – say they have stopped using antibiotic feed additives (although they still use the drugs to control disease outbreaks).

Tyson Foods, the nation’s largest chicken producer, has reportedly slashed antibiotic use in chickens for human consumption by 93 percent, from 853,000 pounds in 1997 to just 59,000 in 2004. Smithfield, one of the nation’s top pork producers, announced last summer that it was cutting back its antibiotic use in adult pigs, and restaurant behemoth McDonald’s has asked all its chicken suppliers to stop using as growth promoters antibiotics that belong to drug classes also used in human medicine.

Two of America’s largest food-service companies, Compass and Bon Appetit, have adopted policies demanding that their meat suppliers curtail antibiotic use.

How big is this problem? Millions of pounds of antibiotics are routinely added to animal feed, and agriculture accounts for an estimated 70 percent of the antibiotics used annually in the United States. That has helped create a growing number of “super-bugs” that are resistant to many antibiotics. Why worry? Meats on supermarket shelves from animals fed antibiotics routinely have higher rates of contamination with antibiotic-resistant bacteria than animals that aren’t given antibiotics.

Moreover, resistant bacteria enter the environment through the nearly 2 trillion pounds of animal wastes produced annually in the United States by animal agriculture. Farm waste run-off can enter rivers, lakes and ground water, and these wastes are often spread on agricultural fields as fertilizer as well. Because of the growing public health crisis of antibiotic resistance, the American Medical Association now opposes the use of medically important antibiotics as feed additives for healthy farm animals.

The Tysons and McDonald’s of the world deserve a lot of credit for responding to a public health problem. Americans can encourage other food companies to follow their example. And to both level the playing field and make sure antibiotic use doesn’t creep back up while nobody’s watching, we are urging Congress to enact legislation sponsored by Sen. Olympia Snowe, R-Maine, that would ban the use of medically important antibiotics as feed additives unless the Food and Drug Administration finds that their use won’t undercut the effectiveness of human-use drugs.

Using antibiotics to treat sick farm animals is one thing. But using antibiotics as routine feed additives to promote growth and compensate for poor conditions is quite another. Fortunately, we may be turning a corner in the fight to end this unsafe practice.

Dr. John Balbus is director of the health program at Environmental Defense, which worked with McDonald’s, Compass and Bon Appetit in developing their policies. He can be reached at jbalbus@environmentaldefense.org. David Yarnold is executive vice president at Environmental Defense and former editor of the San Jose Mercury News. He can be reached at dyarnold@environmentaldefense.org.