London, November 5 : A new study suggests that super-productive modern chickens have, on average, lost over half the genes present in ancestral populations.
Bill Muir of Purdue University in West Lafayette, Indiana, even says that some modern chickens have lost 90 per cent of the genes that were present in ancestral populations.
The researcher said that the new findings indicated that chickens these days lack those characteristics that evolved when they lived in the wild, and might be useful again to help them face stress and disease as livestock.
Inbreeding is a concern with chickens, as the industry is dominated by a few big corporations that produce billions of birds from a handful of private breeding lines.
Muir's team used the recently sequenced chicken genome to measure genetic diversity across these lines, and compared it with 19th century breeds and wild chickens.
The researchers observed that the chickens had already lost a lot of genetic diversity before modern breeders got started.
Muir highlighted the fact that scientists in the 19th century had turned the common European chicken-variably coloured birds with erratically shaped combs that periodically laid clutches of green speckled eggs-into breeds like the White Leghorn, which laid a single white egg daily.
"The basic level of inbreeding was already 10% when modern poultry companies came into being," New Scientist magazine quoted the researcher as saying.
Muir said that that suggested that 10 per cent of the genes of any two birds from the four classic breeds, which were adopted by modern producers, were already identical.
Commercial breeding has pushed this commonality to 15 per cent over the whole industry, making any two chickens more closely related than aunts and nieces in a typical human population, who on average share 12.5 per cent of their genes.
Most of the remaining genetic differences are between different companies' breeding lines that never cross, but much more has been lost within lines.
Lines of chickens bred for eating share at least 30 per cent of their genes, and some lines of laying hens share a staggering 90 per cent of genes, which suggests that they have lost 90 per cent of their potential diversity.
Muir is heading an effort to reintroduce ancestral genes into modern chickens.
The study has been published in the journal Proceedings of the National Academy of Sciences.