American Quarter Horses are renowned for their speed, agility, and calmdisposition. Consequently over four million Quarter horses are used as working horses on ranches, as show horses orat rodeos. New research published in BioMed Central's open access journal BMC Genomics used 'next-generation'sequencing to map variation in the genome of a Quarter Horse mare. Analysis of genetic variants associated withspecific traits showed that compared to a Thoroughbred the Quarter Horse's genome was enriched for variants ingenes involved in sensory perception, signal transduction and the immune system.

Quarter horses have been selectively bred to improve speed over short distances. However they also prone to somedisorders such as hereditary equine regional dermal asthenia (HERDA) where their skin is fragile and tearseasily.

Researchers from Texas A&M University sequenced a Quarter Horse genome with the aim of finding what makes thesehorses so special. They looked at genetic variants, including single nucleotide polymorphisms (SNP), copy numbervariants (CNV), insertions and deletions (INDELs), as well as mutations associated with performance traits anddiseases which are responsible for the makeup of these horses. By comparing the Quarter Horse's sequence with thatof a Thoroughbred, over three million of these variations were found. With the help of a human gene identificationlibrary, pathways, traits and diseases associated with the variations and mutations found in the horse wereidentified.

Dr Scott Dindot from Texas A&M University College of Veterinary medicine explained, "When we compared the genomicsequence of our mare to that of a Thoroughbred genome, we found that the Quarter horse had more genetic variation -especially in genes involved in sensory perception, immunity, and cellular processes. When we looked for diseasecausing mutations and variants associated with performance traits we discovered that the Quarter Horse washeterozygous for a mutation in the cyclophilin B gene which is responsible for HERDA, and a SNP associated withchestnut coat color. The horse also had SNPs associated with racing endurance, originating in Thoroughbreds, whichmay explain the Quarter Horse's speed and stamina."

The sequencing of horse genome has been of great benefit to equine breeders and veterinary medicine because of thepossibilities of improving health and performance. This information can also be used to understand the theoryunderlying horse evolution. Recently mitochondrial sequencing of domestic horses and a Przewalski horse was able toshow that most of the genetic variation between modern breeds was already present in ancestral stock. This newresearch, the first to use next-generation sequencing, has provided information which will be a useful resource inunderstanding the genetic basis behind horse breeds and disease.

http://www.biomedcentral.com/1471-2164/13/78/abstract

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