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Thursday, December 9, 2021

Study indicates reduced genetic diversity in commercialized chickens

If you are wondering why your chicken breast tastes a little blander than usual, it may be because your chicken is lacking the spice of life – diversity.

A study conducted by an international team of researchers, including UC professor and chair of the department of animal sciences Mary Delany, has shown that the commercialized chicken industry around the world has lost at least half of the genetic diversity it once had.

The global commercialized chicken industry raises more than 40 billion birds for both their meat and their eggs. As the industry continues to grow, there is a growing concern for their genetic diversity, according to UC Davis’s animal science website.

In order to study the genetic diversity, the researchers developed a hypothetical ancestral population and compared it to the industrial and research stocks of chickens.

The team used a genome-wide scan to look at different loci – specific locations of a gene on a chromosome – to determine if there were single nucleotide polymorphisms. That is where they saw that the industrial stocks have reduced genetic diversity than their ancestral counterparts, Delany said.

“[The study showed that] the industrial stocks have lost some of the alleles the whole population once carried,” she said.

In the genome of an organism, there are four different nucleotides that make up DNA. The same gene in two different members of the same species can have differences in the sequence of nucleotides called alleles. This difference in the sequence, called single nucleotide polymorphisms, alters the traits that an organism has, causing genetic diversity.

“If you think of a gene that is important for disease resistance and everyone has that same allele, then the population can be decimated if that allele does not protect against a particular disease,” Delany said.

Delany explains that this reduced genetic diversity can be attributed to three main reasons – breed base, artificial selection and consolidation of companies.

Sixty years ago, the commercial chicken industry began and selected specific breeds of chicken to either lay eggs or to be raised for their meat.

The chicken breed chosen for its eggs was the single comb white leghorn. The meat type chickens were a cross between Cornish and Plymouth Rock. This breed base was the foundation for the reduced genetic diversity that is found today because the more they breed within their own populations, the more alleles are lost.

“[Today], we are down to using only one cross breed of chicken [for meat] – the Cornish cross – and a majority of the world is using only the single comb white leghorn breed for egg producing,” said Francine Bradley, a UC Davis cooperative extension poultry specialist.

Another reason for reduced genetic diversity is because of artificial selection. Companies with their breed base only breed within their own populations. They are also bred for economically appealing traits such as larger eggs or increased body mass, Bradley said.

The last cause is more of an economic reason. Many years ago, numerous companies were part of the chicken industry but as the world enters into a global market, companies have consolidated into fewer, larger companies.

This consolidation of companies has led to industry style chicken stocks that have less diversity, Delany said.

“These companies then push their genetics forward [causing reduced diversity],” she added.

Genetic diversity is not completely lost, however.

Ironically, most of the diversity in the species is owned by private “fanciers,” or private chicken owners who raise them as pets or for competitions.

These types include different breeds that are not specifically useful for meat and egg producing but are aesthetically pleasing, Bradley said.

The reduced genetic diversity is not a problem solely in the poultry industry. Other studies either in progress or recently completed have shown similar results in other commercialized species such as turkey, bovines and swine, Delany said.

 

NICK MARKWITH can be reached at features@theaggie.org.

 

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