SALISBURY, Md. — The floors are spotless in Hatchery 3 on the sprawling Perdue compound here. Doors have been rehung to open out, and temperature control and ventilation systems have been upgraded, all to minimize the potential for airborne contamination.

The 1.5 million eggs that arrive here each week to begin the process of becoming the company’s chicken supply are also clean, with none of the traces of feces or feathers that were common in the past. They will move into chambers that are disinfected daily with hydrogen peroxide during the 21-day incubation-and-hatching cycle, a more rigorous program. No human hand will touch the eggs during those three weeks.

It took Perdue roughly a decade to perfect the raising of chickens without antibiotics of any kind, and now it has reached a tipping point: More than half of the chicken it sells can be labeled “no antibiotics ever,” a first for a major poultry company.

Competitors like Tyson and Foster Farms are moving to eliminate the use of antibiotics important to humans from their chicken operations as customers like McDonald’s and Chick-fil-A demand it.

They continue, however, to use ionophores, antibiotics not used in human medicine — a point Perdue is trying to hammer home in new ads featuring Jim Perdue, the chief executive and the grandson of Perdue’s founder.

“Some of my competitors plan to reduce their use of antibiotics over the next few years — but what are you having for dinner tonight?” Mr. Perdue asks in one highlighting the company’s “no antibiotics ever” chicken.

A spokesman for Tyson said the company used antibiotics as little as possible. “We’re working with our research partners on antibiotic alternatives, however, until they’re available we currently plan to continue using ionophores,” the spokesman, Gary Mickelson, said. He added, “We’re not going to compromise animal well-being for marketing reasons.” Foster Farms did not respond to a request for comment.

Antibiotics have long been used in the diets of farm animals to promote growth, control illness and reduce costs. But for several years, public health officials have expressed concern that consumption of meat raised with antibiotics — particularly those used in human medicine — could contribute to antibiotic resistance.

There is scant scientific evidence to suggest that ionophores threaten human health, said Jonathan Kaplan, director of the food and agriculture program at the Natural Resources Defense Council.

Nonetheless, Mr. Kaplan said, Perdue is raising the bar for the poultry industry. “Here is Perdue taking what has traditionally been a niche product and making it mainstream,” he said. “That’s a milestone in this industry.”