A retrofitted henhouse that provides chickens a cage-free environment is up and running in a pilot project to produce millions of cage-free eggs for New England consumers.

The henhouse at Dorothy Egg Farms in Winthrop is longer than a football field and looks like a pulsating, moving brown carpet of chickens, 20,000 of which were brought here three weeks ago in an endeavor that could provide a boost to Maine’s egg industry.

In a joint venture with Dorothy Egg Farms, Radlo Foods LLC of Watertown, Mass., spent hundreds of thousands of dollars to rip out wire cages that once housed more than 80,000 birds. In this new environment, the birds are able to roam, and wood roosts and scratch pads made from artificial turf simulate barnyard conditions.

This is the first large-scale conversion of a conventional henhouse in Maine, and possibly the first in the nation, according to Radlo Foods.

Chickens that aren’t confined enjoy better living conditions than birds stacked in cages, according to animal advocates who have developed a humane certification program.

Cage-free is just a tiny slice of Maine’s $61 million-a-year egg industry, but sales are growing at a double-digit pace. In fact, demand for the certified eggs is growing so fast that Radlo and Dorothy plan to convert a second conventional chicken house to a cage-free one.

“The way the trend is going, you’re going to see a lot more of this,” said David Radlo, the company’s president and chief executive officer.

Commodity egg farms typically have millions of birds that live in stacked narrow cages, which has led animal rights activists to put pressure on both producers and supermarkets.

In response, many of the nation’s big egg producers have adopted new care guidelines, such as having more cage space and better food, water and ventilation. Eggs that meet these standards are sold in cartons with a check-mark seal from the United Egg Producers.

The eggs Radlo is producing in the Winthrop henhouse meet even stricter rules set by Humane Farm Animal Care, a Virginia-based food animal rights group.

To earn the group’s Certified Humane label, egg producers must follow guidelines that run 29 pages and include things such as the number of square feet per chicken to how roosts are constructed.

Here in the converted Winthrop henhouse, birds are able to roam the vast, wood-slat floor. Feed trays and water tubes hang from the ceiling, and light comes from overhead, compact-fluorescent bulbs. Metal nesting houses line the walls, and eggs laid inside travel by conveyor belt to a central collection point.

The hens in this project are 25 weeks old, and they’re still being trained to lay in the nesting boxes. Ten times a day, workers pick up eggs laid on the scratch pads and floor.

This is not a cheap production process.

Only 20,000 birds live in the henhouse, where 80,000 once lived, and additional workers are needed to manage the operations. A special vegetarian feed costs 25 percent more than conventional feed.

But Radlo can get a higher price for the eggs, which are sold under the Radlo’s Born Free and Eggland’s Best brands and sell for $2.99 a dozen at Shaw’s, nearly double the price of a dozen large store-brand eggs that sell for $1.69.