Thoroughbred "Performance Genes" Further Examined in Study

The genetics behind the athletic performance of Thoroughbred racehorses has been a popular area of research in the past few years. A large-scale study was carried out recently in Japan, the results of which corroborate those of previous studies: Identifying specific "performance genes" on equine chromosome 18 could identify the ideal distance for a Thoroughbred to race. Some industry veterinarians, however, suggest that this information should still be evaluated and used with caution.

Researchers on four separate studies have previously identified a region of DNA on chromosome 18 (which the researchers referred to as ECA18) that they believe could be associated with racing performance. One of the research teams found a specific mutation in the myostatin gene (MSTN) located on ECA18. Researchers also previously evaluated the myostatin mutation and determined that it contributes to muscle hypertrophy (enlargement) and might be useful in predicting whether a horse is better suited for short-, mid-, or long-distance races.

To further assess the ECA18 genes' influence on athletic performance, Teruaki Tozaki, PhD, from the Laboratory of Racing Chemistry's Department of Molecular Genetics in Tochigi, Japan, recently analyzed genetic material from blood samples collected from Thoroughbred racehorses registered with the Japan Racing Association and born between 1993 to 2000 in Japan.

Tozaki's team identified four specific genetic mutations (single variations in the DNA) called single nucleotide polymorphisms (SNPs) on ECA18 within or near the MSTN gene using standard polymerase chain reaction (PCR) and genetic sequencing techniques. Then they compared genetic sequences of these SNPs in 1,710 horses with performance records including most successful race distance, win-race distance (i.e., the average distance of races won), performance rank, and lifetime earnings.

Tozaki noted, "SNPs on ECA18 in both male and female Thoroughbred racehorses were clearly associated with performance, most notably optimal race distance."

According to Tozaki, these results indicate that there is at least one gene or a combination of genes or SNPs in this region of ECA18 that likely influences a Thoroughbred's optimum race distance.

"Regulation of the MSTN gene appears to affect racing performance and ... these SNPs could be genetic diagnostic markers for racing performance indicators, as we previously suspected," Tozaki explained.

Presently, Tozaki's team is focusing on the physiologic characteristics of Thoroughbreds with the MSTN mutation and how they relate to racing performance. For example, they're looking at the differences in muscling among young horses not in training, those in training, and horses actively racing.

Although this study is included in a large group of related studies, a recently released statement from the American Association of Equine Practitioners (AAEP) indicates that industry veterinarians are still interpreting the results with caution: "The interpretation of the tests results may not be simple, and the predictive value of the tests may not be high. The AAEP supports the use of evidence-based tests for medical and performance related genetics if the methodology and results have been published in peer-reviewed journals and withstood appropriate scientific scrutiny."

The study, "A cohort study of racing performance in Japanese Thoroughbred racehorses using genome information on ECA18," is scheduled to be published in an upcoming edition of the journal Animal Genetics. The abstract is available online.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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