Selection in Australian Thoroughbred horses acts on a locus associated with early two-year old speed.
Authors: Han Haige, McGivney Beatrice A, Farries Gabriella, Katz Lisa M, MacHugh David E, Randhawa Imtiaz A S, Hill Emmeline W
Journal: PloS one
Summary
# Editorial Summary: Selection for Early Two-Year-Old Speed in Australian Thoroughbreds Regional racing industries select for distinct traits shaped by their specific conditions, and this study identifies the genetic basis of one such adaptation in Australia. Researchers compared genomic data from 99 Australian and non-Australian Thoroughbreds to locate selection signatures, then used genome-wide association analysis in 179 two-year-olds to pinpoint genes affecting early speed, validating findings in a larger cohort of 922 horses. Three chromosomal regions showed strongest differentiation in Australian horses—particularly on ECA14 (33.2–35.6 Mb)—containing genes involved in cardiac function, neuromuscular development, stress response and skeletal muscle physiology; a specific SNP within the PCDHGAP5 gene on ECA14 was associated with elite racing performance. Australian breeding programmes appear to have preferentially selected for genetic variants promoting early two-year-old speed and favourable racing temperament, representing an adaptation to local racing conditions rather than universal performance traits. For professionals advising breeding decisions or managing young racehorses, this research underscores that performance genetics are geographically and contextually specific; what constitutes an 'ideal' genotype varies considerably by region and racing expectations, which has implications for importing bloodlines and interpreting genetic predispositions to injury or performance.
Read the full abstract on PubMed
Practical Takeaways
- •Australian-bred Thoroughbreds carry distinct genetic variants selected for early two-year-old speed; breeders should be aware these regional genetic signatures may influence performance timing and adaptation to racing
- •The PCDHGC5 locus and surrounding protocadherin gene cluster represent potential genetic markers for identifying young horses with inherited predisposition to early speed—useful information for selection and racing planning
- •Understanding that Australian bloodlines have been selected for genes modulating muscle physiology and locomotion under local conditions may help explain performance differences when these horses compete internationally or in different training environments
Key Findings
- •Selection signatures on ECA6, ECA14, and ECA16 differentiate Australian from non-Australian Thoroughbreds, with candidate genes involved in cardiac function, locomotion, and skeletal muscle response to exercise
- •A SNP within PCDHGC5 gene on ECA14 (33.2-35.6 Mb) is associated with elite racing performance in a cohort of 922 horses
- •Australian breeders have selectively bred for genetic variants affecting behaviour, locomotion, and skeletal muscle physiology that contribute to early two-year-old speed
- •Geographic variation in racing ecosystems has resulted in regional selection for different traits, detectable through pan-genomic SNP analysis