The effects of inbreeding on Thoroughbred racehorses

A scientific study conducted by researchers at the University of Sydney has uncovered breeding strategies to improve the athletic success of Thoroughbred racehorses.

The researchers found that horses with higher levels of inbreeding tended to have reduced athletic ability. Thoroughbred horses are often mated with related individuals in order to select for desirable traits, ultimately leading to horses with great athletic ability that will win more races and earn more prizemoney. But this inbreeding can also lead to reduced health.

This study was based on an analysis of the racing performance and pedigree records of over 135,000 horses. One of the key findings was that the slow pace of inbreeding, which has occurred over many generations, has selected for genes that have improved the overall athletic performance of the population.

PhD student Evelyn Todd, who began this research as an Honours student in the MEEP Lab, said: “These results show that although some inbreeding between horses with superior racing performance may be beneficial, close inbreeding events should be avoided where possible”.

The Thoroughbred horse population is unique in that every contemporary individual traces its ancestry back to the 18th century, when the breed was founded. The researchers discovered that some of these founding horses have variable influences on the racing success of their present-day descendants. Remarkably, inbreeding to one founder, Herod (born 1758), has increased the athletic ability of his modern descendants.

This research provides important information for the Australian Thoroughbred breeding industry, which makes a significant contribution to the national economy.

Read the scientific publication here:
Founder-specific inbreeding depression affects racing performance in Thoroughbred horses
Todd, Ho, Thompson, Ang, Velie, Hamilton (2018) Scientific Reports, 8: 6167