The Welfare and Safety of the Racehorse Summit meetings began in 2006 with the objective of improving the safety and soundness of the Thoroughbred racehorse. One of the central questions resulting from these meetings was whether the genetic structure of the population had become compromised, such that the Thoroughbred had become less sound and durable during the last few decades. Powerful genomic tools are now available to address this question.
As a first step to do so, we used whole genome sequencing to identify every base of DNA in an animal’s genome. We studied the genomes of two groups of U.S. Thoroughbred horses: Group 1 (82 horses born between 1965 and 1986) and Group 2 (103 horses born between 2000 and 2020). Previous genetic studies used methods that measured, at most, 0.03% of the DNA to report statistically significant increases in inbreeding over time. “Statistically significant” is a scientific term meaning that there is a difference between measured groups, but does not address the magnitude of the difference nor its consequence. Using the whole genome sequence of each horse, we calculated its inbreeding coefficient, which is illustrated in the Figure below, taken from our recent publication.
