Texas A&M study finds domestic horse breed with third lowest genetic diversity

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A new study from Dr Gus Cothran, professor emeritus at the Texas A&M School of Veterinary Medicine & Biomedical Sciences (CVM), has found that the Cleveland Bay (CB) breed of horses has the third lowest level of genetic variation in domestic horses, ranking higher than the notoriously inbred Friesian and Clydesdale breeds. This lack of genetic diversity puts the breed at risk for a variety of health issues.

Genetic variation refers to the differences between the DNA codes of different individuals. Populations with high genetic diversity will have a wider range of different traits and will be more stable, in part because the disease traits will be more diluted. In populations with low genetic variation, many individuals will have the same traits and be more vulnerable to disease.

The CB is the oldest established breed of horse in the UK and the only native warm-blooded horse in the region. Used for recreational riding, driving and equestrian competition, the CB is considered a critically endangered breed by the Livestock Conservancy.

Because maintaining genetic diversity within the breed is important to securing the future of horses, Cothran and his team worked to obtain comprehensive genetic information about the breed in order to develop more effective conservation and selection strategies. .

In this study published in The diversity, the researchers genotyped the hair of 90 different CB horses and analyzed their data for certain genetic markers. These samples were then compared with each other, as well as with samples from other breeds of horses to establish genetic diversity within the breed and between other breeds.

Both heterozygosity and the average number of alleles for the breed were below average, indicating below average genetic diversity within the breed. This low genetic diversity must be considered as a warning signal for possible health problems.

“Low diversity is a marker of inbreeding, which can lead to low fertility or a number of hereditary diseases or malformations,” Cothran said. “With the total population number for the breed being so small, such problems could quickly lead to the breed’s extinction.”

The Cleveland Bay Horse Society of North America estimates that there are only 900 CB horses in the world. These low numbers mean that the breed is considered extremely rare.

This study also assessed the diversity between BC and other breeds using a majority rule consensus tree, a type of analysis that shows an estimate of how different clades, or groups of organisms sharing a common ancestor, could nest on their ancestral tree.

Analysis by Cothran and his team revealed that CB did not show any close relationship with other races, including other races of the same clade. Although this may be the result of the low genetic diversity within the breed, these data suggest that BC is genetically unique compared to other breeds. These results emphasize the importance of CB horses as a genetic resource.

“The CB is an unusual horse in that it is a fairly large sized horse, but it is built like a saddle horse rather than a draft horse,” Cothran said, noting the uniqueness of the race. “He is frequently mated with other breeds such as the Thoroughbred to create eventing or show jumping horses, although this poses a potential threat to maintaining diversity in BC.”

Cothran hopes his research will help inform conservation efforts supporting the longevity of the CB breed, as well as educating breeders on how they can more responsibly develop their horses’ genetic lines.

“If any evidence of inbreeding is seen, breeders should report it to scientists for further analysis,” Cothran said. “Efforts should be made to keep the number of CB horses as high as possible and to monitor breeding practices to minimize inbreeding and loss of variability.”

“Domesticated animals, including horses, are also threatened with declining populations, as are endangered species, but research can help determine which populations (breeds) are at risk and provide possible guidance to help. reduce the risks or consequences, ”he said.

Although CB horses are currently at risk, Cothran remains optimistic that careful monitoring and management of the breed can preserve them as a cultural and genetic resource for years to come.


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