Cramped chicken cages are going away. What comes next?

For the past two years, at an undisclosed location in the Upper Midwest, a large commercial egg farm has been probed with every tool of modern science. Researchers have collected data on feed consumed, eggs produced, rates of chicken death and injury, levels of dust in the air, microbial contamination and dollars spent. Graduate students have been assigned to watch hours of video of the hens in an effort to rate the animals' well-being.

It was all intended to give farmers — and, perhaps, consumers — a clearer picture of different ways to house the chickens that lay our eggs. Three different types of chicken houses exist on this farm: traditional wire cages; "enriched" cages that offer more space, perches and nesting boxes; and cage-free houses in which chickens get to move around freely.

An industry consortium called the Coalition for a Sustainable Egg Supply funded this study, mainly because chicken housing is now controversial. California has banned eggs from chickens that don't have enough space to turn around or flap their wings. Other states are considering similar laws.

The egg industry is meanwhile looking for alternatives that won't be declared illegal. This study is a close look at a couple of those alternatives.

"The conventional cage system is not going to be the system of the future," says Janice Swanson, a professor of animal behavior and welfare at Michigan State University and co-director of the chicken housing study. The transition away from cages, in fact, is already underway. "Very few conventional cage systems are being installed" on egg farms these days, says Joy Mench, a professor of animal science at the University of California, Davis, the study's other co-director. Cal-Maine Foods, for instance, the largest producer of shell eggs in the U.S., is no longer building new chicken houses with traditional cages, says Matt Arrowsmith, the company's vice president for purchasing. Traditional cages still account for 90 percent of the company's production, but when those houses wear out, they will be replaced with either cage-free houses or enriched cages, sometimes called colony cages.

Swanson and Mench began presenting results from their study this week to egg producers, processors and marketers. "Our goal is to identify the trade-offs between the three systems for them to consider as they're making decisions about what systems to install," Swanson says. Scientific reports also are appearing in the journal Poultry Science.

According to this experiment, some trade-offs are clear. Cage-free houses allow chickens a wider range of natural behavior. Their bones also were stronger, as a result of being able to move about freely.

On the other hand, in part because of that freedom, "there's more potential for injury," Swanson says. This is one reason more chickens died in the cage-free house — more than 10 percent, compared with about 4 percent in the cages. Most died from disease, but some also died because of injury or from being hen-pecked.

Air in the cage-free house was full of dust, but "it didn't seem to have any effect on the hens," says Mench.

From the perspective of economic efficiency, though, cages were a clear winner. Chickens in both traditional and enriched cages produced more eggs and produced them more efficiently, compared with cage-free houses. Operating costs of the cage-free house were 23 percent higher than for traditional cages, and even more when the capital cost of building the house was included. Cage-free production was expensive in part because the farmer had to pay more for young hens, or pullets, that had been raised in a cage-free environment.

On the other hand, egg producers also are responding to consumer demand, and "there is a growing demand for cage-free," says Arrowsmith of Cal-Maine Foods. Most consumers, though, still buy the cheapest eggs on the shelf, Arrowsmith says, and that will keep keep most chickens in some sort of cage for a long time to come.

Cal-Maine Foods is hedging its bets, producing eggs that carry a variety of labels, depending on how they are housed and fed: cage-free, omega-3 or vegetarian. "The more diverse products that you can put on the shelf, the more likely it is that a consumer will want one of them," Arrowsmith says. Copyright 2019 NPR. To see more, visit https://www.npr.org.