Four of the nation’s top 10 chicken producers have virtually ended a practice that health and activist groups for years charged was causing a public health crisis: feeding broiler chickens low doses of antibiotics to make them grow faster and stay healthy.

Tyson Foods, Gold Kist, Perdue Farms and Foster Farms say they stopped using antibiotics for growth promotion. In addition to ending a practice that Europe banned and McDonald’s ended a month ago, the four companies also have severely limited antibiotic use for routine disease prevention, though antibiotics are still used to treat disease outbreaks.

Tyson Foods, the nation’s largest chicken producer, has led the way with a 93% reduction, from 853,000 pounds in 1997 to just 59,000 in 2004. In 2004, less than 1% of the company’s broilers received antibiotics, says chief veterinarian Patrick Pilkington.

Perdue Farms stopped using antibiotics for growth promotion about five years ago. “It became obvious that it was a concern,” says chief veterinarian Bruce Stewart-Brown. Now at any given farm in the system, only one flock in five years receives antibiotics, either to halt a disease outbreak or because birds are threatened with infection, he says.