Stunning gains in poultry achieved over the past century have come at a cost, according to a study by researchers from Purdue University in Indiana.
Bill Muir, an animal sciences professor at the university, said a recent study has found that more than half of the genetic diversity in the world’s poultry was lost before 1950.
“The poultry companies knew that the genetic base was narrow, but what they didn’t know was how narrow it actually was,” said Muir, who helped write the study recently published in the Proceedings of the National Academy of Sciences.
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“My hope is that they might take the results of this study and decide to start bringing some other breeds in.”
Intensive breeding and selection of chicken for commercial purposes that got underway in the 1920s focused on only three or four out of the hundreds of breeds worldwide that could have been chosen, he said.
Those few breeds were eventually developed into the white Cornish chickens universally raised for meat production and white leghorns for eggs that have come to dominate the global egg industry.
Using the recently sequenced chicken genome, Muir and his fellow researchers compared commercial lines with wild or non-commercial birds and found that in some cases, 90 percent of the alleles, or genetic markers, in commercial birds had been lost.
This lack of diversity could pose a “potential risk” to the world’s poultry in the form of new diseases or lack of future adaptability.
“If there is less genetic variability in a population, then that means that there is less chance that you will have an individual that is resistant,” he said.
“I would say that probably commercial populations are less likely to have a resistant allele than a wild population.”
The potential risk to the industry of disease is real.
The ongoing effort to stamp out avian influenza, which first appeared in Asia in early 2004, has seen millions of birds fall victim to the virus or culled in efforts to halt the outbreak, and scores of human fatalities.
Muir said that his study shows the need for the preservation of rare breeds of poultry, which could act as a critical reservoir of genetic diversity.
Current commercial poultry populations, however, are too small to benefit from the continuous evolutionary changes that arise naturally through genetic mutation.
“It’s like a tank of gas. We’re using up that limited variability without adding much that’s new to it,” said Muir.
“When that becomes exhausted, which may not occur for another 50 or 100 years, where are they going to go to replenish it?”
The main point of his study, added Muir, was to provide a convincing argument to kick start the process of adding diversity to commercial breeds, so that more genetic lines of highly efficient egg and meat producers could be developed.
“If we could start doing that slowly and surely now, it would be a lot more beneficial than waiting until we get into trouble and say, ‘Now what are we going to do?'”
On the plus side, the success in terms of feed efficiency in modern chickens has been staggering.
For every two kilograms of grain fed to modern broilers, mainly corn and soybean meal, one kg of meat can be produced, amounting to a 2:1 feed conversion ratio or greater.
In a study published in 2003, Gerald Havenstein and others from North Carolina State University compared the performance of modern broiler chickens and a strain commonly used on farms in 1957.
He found that 90 percent of the improvements in feed conversion efficiency and growth rate could be attributed to genetic improvements in the animals, not improved nutrition.
At 84 days on feed, the 1957-era chickens weighed 1.4 kg, while the modern Ross 308 broilers tipped the scales at a whopping 5.5 kg.
The modern broiler on the 2001-style rations reached 1.8 kg at 32 days of age with a feed conversion ratio of 1.47, whereas the 1957 birds would have taken 101 days on their much less efficient feed conversion ratio of 4.42.
Armed with superior rates of gain, global poultry production has soared by an estimated 436 percent since 1970, the study found, and now chicken is the most commonly consumed meat on the planet.
Two giant companies control the world’s supply of broiler genetics, and two others supply the layer industry, using a handful of proven lines.
Broilers, which come from three breeds, are slightly more diverse than layers, which are based on only one breed.
That’s because broiler female lines must be bred for egg production as well as meat attributes in the parent stock segment, he said.
The new trend aimed at tapping niche markets in parts of Asia and Europe of breeding common meat lines with coloured chickens to create a terminal cross with a different meat flavour is a step in the right direction in this regard.
However, efforts aimed at widening the genetic base must be broader in scope, he said.
“All white eggs in commercial production come from white leghorns. So the white leghorn is like the Holstein of the poultry world. That in itself is the problem. We’ve literally put all our eggs in one basket,” said Muir.
“We showed in the study that essentially, any white leghorn population, no matter whether it came from this company or that company, or if it belonged to a university, they’re all the same.”
