Modern industrialized agriculture depends to a large degree on uniformity. Crops such as corn, rice, wheat and soybeans are all bred to have predictable characteristics so they can be more efficiently planted and harvested by machine. Livestock, too, are easier to house, feed and market if the animals share important traits like size or their yield of milk, meat or eggs.

But research published this week indicates that in the chicken industry, the goal of a uniform product has shouldered aside another important goal - genetic diversity among commercial chicken flocks. VOA's Art Chimes reports.

When I go to the supermarket, I see packages of chicken all lined up, all looking pretty much the same. Now, a new study has examined that similarity on the DNA level.

"We looked at all of the commercial chicken, layer and broiler production in the world, and it was amazing that actually there's very little variability among the commercial birds," says William Muir, a professor in the Animal Sciences Department at Purdue University.

He's the author of a new paper that quantifies the decline in genetic diversity on commercial chicken farms throughout the industrialized world.

"This is a worldwide problem, and that's the uniqueness of the paper, is that we essentially assayed the entire world's diversity of poultry to determine what is missing," Muir says.

Breeders 'Perfect' Chickens for Mass Production

The uniformity of the commercial chicken population is not accidental. Professor Muir offers a brief history lesson. The first domesticated chickens were used as fighting game birds. Later, farmers bred them for eggs and meat - with some breeds selected for pleasing color, others for local climate conditions, and so on. Eventually, a large number of standard breeds was developed.

Then, about a century ago, large commercial chicken farming began, and companies looked for breeds that would be well-suited to mass production.

"And for their broilers, the one for meat, it turned out to be a cornish variety. And the cornish was actually a game bird, one that was actually made for fighting. Because of its huge, large breast, it could force its way in, and it's very powerful. Whereas the layers, we wanted a bird that would put all its energy into making eggs," Muir explained.

"So they found that the white leghorn was nearly perfect for that. And they said, 'Well, we'll just use this bird. It's already there most of the way. We're 90 percent of the way there. Let's just use it,'" Muir says. "And that's exactly what they did. And so since that time, they just used these one of 100 breeds and further perfected them."

What Muir calls "perfecting" actually means breeding out the little remaining strains of other breeds, so that each of the thousands of chickens in the huge flocks raised by commercial farmers would be as identical as possible to the one in the next cage.

Genetic Uniformity Means Birds May Be More Susceptible to Disease

Such uniformity sounds like a dream for someone running a mass production process. But there's a downside to this lack of genetic diversity: it raises the risk that all these nearly-identical birds could be susceptible to a common threat - such as a disease.

"When it comes to trying to find resistance to new disease or trying to make a better product, genetics works on diversity. So here we're concerned that we don't have enough genetic diversity to meet future challenges. That's at the root of the whole problem," Muir says. 

Genetic diversity might make managing flocks more difficult, but Muir says it could also improve their odds of surviving a potentially disastrous disease such as avian influenza.

"If avian influenza comes along, they can have the bird that's resistant to it ... you won't have a monoculture, when one disease hits it, and it wipes it out. Then what are you going to do? Well, that's the problem. What are you going to do?" Muirs asks. 

Expert Says Now Is Time to Breed for Disease Resistance

Bringing some disease-resistance back into commercial flocks would mean first identifying birds that have the resistance and then breeding them with the commercial leghorn and cornish breeds. 

"Somewhere in your wild population there hopefully would be a resistance, but getting that back into the commercial population could be a problem," Muir said. "They need to start now in terms of integrating that biodiversity back into some commercially viable products."

But Muir says that would be a challenge - and an expensive one. The disease-resistant birds' genetic heritage was excluded from the commercial breeds in the process of making them more commercial. So breeding in resistance, for example, to avian flu might dilute other characteristics that commercial producers value.

And where are these disease-resistant birds likely to be found? Well, one place to look is places where chickens are raised by small farmers or even families who keep a fewbirds in the yard for food.

"Actually, it's your small producers [who] have the genetic diversity that we need. So they're maintaining it," Muir says. "?The reservoir[s] of genetic diversity are these small populations, the small producers. The big multinational corporations, they want to maximize efficiency, and they want to maximize the return on investment. That's where we're having the problems."

Although William Muir's study was specifically about chickens, he says the same pattern exists in other areas of large-scale commercial agriculture. Ninety percent of the U.S. milk supply, for example, comes from the Holstein breed of cattle.

Muir's study on genetic diversity in chickens was published online this week by the Proceedings of the U.S. National Academy of Sciences.