“We have a commodity at risk because it has a narrow genetic base.”
– Bill Muir, Purdue University
If you’re old enough, you can probably remember a variety of hens – Barred Rock, Rhode Island Red, New Hampshire, all with differentcoloured plumage – strutting about the farmyard. During the week they laid eggs. On Sunday, they became dinner.
Half a century ago, a hundred or more breeds of poultry could be found on farms throughout North America. Since then, modern breeding techniques have practically eliminated the dual-purpose chicken. You can still find some in backyard fancy flocks. Otherwise, a mere handful of breeds dominate today’s commercial broiler and layer industries.
Breeding for special traits greatly improves production. But it does so at the expense of the gene pool. In the case of poultry, modern breeds have lost much of their genetic diversity, leaving them open to a possible industry collapse, according to a new study.
A U. S.-based international research team has found that commercial chickens are missing at least half of their genetic diversity because breeding programs have narrowed the genetic base over the years.
That’s serious because chickens may not have the tools necessary to ward off new diseases, such as the H5N1 avian influenza spreading throughout parts of the world.
“Don’t bother me”
“I want to be sure we have enough genetic variability to address future concerns and future needs,” said Bill Muir, a research team member and an animal sciences professor at Purdue University.
Unfor tunately, moder n breeders don’t often consider loss of diversity because they’re too busy concentrating on specific genetic traits to boost production and make more money, Muir said in a recent telephone interview from West Lafayette, Indiana.
“There’s a complacency in the sense that the commercial people are still making progress for egg numbers, they’re still making progress for efficiency, they’re still making larger birds for meat. So (they say) ‘There’s no problem here, we’re still making lots of progress, we must have lots of genetic variability left, so don’t bother me.’
“Just because you’re making progress doesn’t mean you have all the genetic variability you need.”
Muir and his colleagues arrived at their conclusions by obtaining DNA samples from poultry around the world and identifying the number of alleles found throughout. (An allele is one member of a pair of genes controlling the same trait and occupying a specific position, or locus, on a chromosome.)
Researchers recreated a theoretical ancestral bird population by taking the average allele frequency across those samples. The team compared those alleles with commercial breeds to see what was missing. They found at least 50 per cent of alleles lacking in commercial lines.
Fewer alleles means fewer versions of genes in a gene pool. This provides less potential for developing different traits. It also narrows the ability of the gene pool to evolve.
“Half the chance”
Muir used a gambling analogy to illustrate the problem.
“You can’t hit the jackpot in Las Vegas without putting coins in the slot. You never know if you’re going to hit the jackpot but you know you are going to have to have coins in order to hit it. Now if I take away half your money, what’s the probability you’re going to hit the jackpot? Well, it’s halved. That’s essentially the analogy.
“If you take away half the alleles, you have only half the chance of having the one you need.”
Although it’s impossible to say precisely what traits are missing, Muir worried commercial chickens may lack the genetic ability to adapt to, and resist, certain diseases, such as the H5N1 avian flu.
It isn’t just new diseases, either. Muir said existing viral diseases such as avian leukosis, Marek’s and Newcastle are constantly changing and chickens with decreased immunity may not be able to keep up with them, despite vaccines.
“The bottom line is that we have a commodity at risk because it has a narrow genetic base,” he said.
“I’m saying I want to be sure we have enough genetic variability to address for future concerns and future needs.”
Muir said breeding companies should bring in genes from other standard breeds and crossbreed them into new products to produce birds with a new genetic base.
Not having proper genetic resistance can be potentially devastating to agriculture, as certain incidents show.
Dur ing the 1950s and 1960s, the Texas male-sterile cytoplasm (cms-T) was used extensively in commercial corn to eliminate tassel. But it also increased disease susceptibility. In 1969 and 1970, the southern corn leaf blight nearly destroyed the U. S. corn crop because over 85 per cent of it carried cms-T. [email protected]