Thoroughbred horses are selectively bred to improve both speed and stamina in an attempt to create the perfect racehorse. With the knowledge gleaned from the completion of the equine genome and advanced laboratory techniques available to genetic researchers, it seems this seemingly fleeting feat could be nearly within breeders' grasps.
Previous research by Teruaki Tozaki, PhD, from the Department of Molecular Genetics at the Laboratory of Racing Chemistry in Tochigi, Japan, and colleagues found a region on equine chromosome 18 (ECA18) that is associated with racing "phenotypes," or characteristic traits, such as optimal racing distance.
"Addition research ... has shown that specific regions of ECA18 can potentially predict racing performance in Japanese Thoroughbred racehorses," said Tozaki. This part of ECA encodes a protein called myostatin, which is involved in controlling both the number and growth of skeletal muscle fibers.
"This study was therefore designed to look at the relationship between the mysotatin gene (MSTN) and various physical characteristics of Thoroughbred horses prior to training such as body weight, wither height, and chest and cannon bone circumference," Tozaki explained.
Tozaki and colleagues collected blood samples from 116 male and female Thoroughbred horses at 18 months of age when they were introduced to a training center to begin training. Physical characteristics were measured for six months and DNA was extracted from the blood samples so the genetic code on ECA18 could be analyzed.
Upon reviewing the results of their study, researchers found that physical characteristics, such as body weight-to-withers height ratio, were significantly different between horses with different genotypes on EAC18. Specifically, male horses with a genotype previously shown to be suitable for short-distance racing had the highest body weight-to-withers height ratio, and horses with the genotype previously shown to be suitable for long-distance raging had the lowest body weight-to-withers height ratio.
"Male horses with specific genotypes on EAC18 seem to be suited to short-distance races and show a particularly mature tendency with respect to their physical development, and therefore could make their racing debuts at an earlier stage than horses without these specific genotypes," noted Tozaki.
Alternatively, female horses with a genotype supporting their use as long-distance runners likely require longer training periods before they are suitably conditioned for competition.
"Based on our knowledge of EAC18 and the MSTN gene, we suggested that the MSTN gene influences skeletal muscle mass, ergo racing performance, particularly optimum race distance," concluded Tozaki.
According to the study, these findings add an additional stone in the pathway to developing effective training and racing regimes that can be tailored to each individual Thoroughbred racehorse based on their genetic makeup, although it's believed that other genetic and environmental factors influence racing performance.
The study, "Sequence variants at the myostatin gene locus influence the body composition of Thoroughbred horses," will be published in an upcoming edition of the Journal of Veterinary Medical Science. The text is available online.
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