Genomic analysis of 370 Japanese Thoroughbred horses: the genetic background of why Thoroughbreds can run fast

Humans have been trying to improve Thoroughbreds by selectively breeding horses that can run fast. Each generation, a small number of males are selected to breed so that only these “elite” males can pass on their genes to the following generation. In this study, we examined how this continuous artificial selection has affected the evolution of the genomes of Thoroughbreds. First, we found that the genetic diversity is low in Thoroughbreds due to repeated inbreeding since even before the establishment of Thoroughbreds. Second, we found several regions that exhibit signatures of artificial selection. These regions typically show locally reduced genetic variation and should contain genes that are important for the athletic performance of Thoroughbreds. This study opens the way for genomic information to be utilized in the selective breeding of Thoroughbreds.