The genetics of selective breeding in Thoroughbred horses

Abstract

This thesis examines the effects of selective breeding practices on the Thoroughbred horse population. The Thoroughbred horse breed was founded in the 18th century and the studbook has been closed since 1791, resulting in contemporary Thoroughbred horses being the result of many generations of inbreeding for the intensive selection of athletic performance. Selective breeding can result in genetic improvement through increasing the frequency of variants pertaining to desirable traits and may also potentially remove harmful alleles from a population. However, an increasing body of evidence has shown that many domestic animal populations harbour high levels of deleterious variants as a result of population bottlenecks and low effective population sizes from selective breeding practices. Until now, no studies have reported the effects of these breeding practices on the Thoroughbred horse population.

The findings of this thesis provide important insights into the effects of selective breeding on genetic load and genetic gain in the Thoroughbred horse population. These insights can be used to assist breeding decisions in Thoroughbreds to increase genetic improvement in the population. The findings of this thesis not only have important economic implications for one of the largest domestic animal populations in the world, but also have the potential to improve welfare standards in an industry under increasing scrutiny. More broadly, this thesis provides insights into the effects of selection, inbreeding and population bottlenecks on the health and fitness of domestic breeds. The methods used in this thesis can be applied to other animal populations to improve breeding and population management decisions.