Low genetic diversity in Britain’s oldest horse breed – study

A horse drawn carriage in Cleveland Bay in the Netherlands. Photo: Les Meloures CC BY-SA 2.5

Britain’s oldest established horse breed has the third lowest level of genetic variation among domestic horse breeds, new research shows.

In terms of genetic diversity, the Cleveland Bay horse manages to rank above the Friesian and Clydesdale breeds.

This lack of genetic diversity puts the breed at risk for a variety of health issues.

The research was conducted by Dr. Gus Cothran, professor emeritus at the Texas A&M School of Veterinary Medicine & Biomedical Sciences.

Genetic variation refers to the differences between the DNA codes of different individuals.

Populations in which genetic diversity is high will have a wider range of different traits and 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 Cleveland Bay is Britain’s oldest established breed of horse and the region’s only native Warmblood horse. Used for recreational riding, driving and equestrian competition, the Cleveland Bay 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 their study published in the journal The diversity, the researchers genotyped the hair of 90 different Cleveland Bay 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 explains. “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 purebred horses in Cleveland Bay in the world. These low numbers mean that the breed is considered extremely rare.

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

Cothran and his team’s analysis revealed that Cleveland Bay does not exhibit 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, the genetic information gathered suggests that the Cleveland Berry is genetically unique compared to other breeds.

These results emphasize the importance of breed as a genetic resource.

“The Cleveland Bay 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 breed.

“It is frequently mated with other breeds such as the Thoroughbred to create eventing or show jumping horses, although this is a potential threat to maintaining diversity in the race. Cleveland Bay. “

Cothran hopes his research will help inform conservation efforts supporting the longevity of the breed, as well as help breeders 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 Cleveland Bay horse numbers 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 Cleveland Bay horses are currently in danger, 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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