Origin and spread of Thoroughbred racehorses inferred from complete mitochondrial genome sequences: Phylogenomic and Bayesian coalescent perspectives.
Authors: Yoon Sook Hee, Lee Wonseok, Ahn Hyeonju, Caetano-Anolles Kelsey, Park Kyoung-Do, Kim Heebal
Journal: PloS one
Summary
# Editorial Summary Thoroughbreds underpin modern equine sport and have profoundly shaped other horse breeds globally, yet their genetic origins and population dynamics remained poorly characterised until now. Researchers sequenced complete mitochondrial genomes from 14 Thoroughbreds and analysed them alongside 151 existing horse sequences from diverse breeds using phylogenomic and Bayesian coalescent methods, establishing temporal and spatial evolutionary patterns. The findings revealed that Thoroughbreds derive from multiple maternal lineages with closest relationships to Asian, Middle Eastern, and European breeds—notably not directly descended from Przewalski's horses—with their most recent common ancestor dating to approximately 8,100–111,500 years ago, substantially younger than the broader modern horse population (2.7 million years). Population expansion in Thoroughbreds and related domestic horses occurred roughly 5,500–11,000 years ago, aligning with the domestication period, suggesting selection and breeding practices have substantially shaped contemporary bloodlines. These mitogenomic insights offer practitioners and breeding programmes a genetic framework for informed decision-making on bloodline management, parentage verification, and conservation priorities, whilst establishing a foundational dataset for ongoing equine genomic research.
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Practical Takeaways
- •Understanding the diverse maternal genetic origins of Thoroughbreds can inform selective breeding programmes and help predict breed-specific health or performance traits
- •The recent common ancestry of Thoroughbreds (within 10,000+ years) versus ancient horse domestication suggests modern racing breeds were refined relatively recently and may share genetic vulnerabilities
- •Genetic history data now available for Thoroughbreds can support conservation efforts and guide crossbreeding strategies to improve other horse breeds
Key Findings
- •Thoroughbred racehorses have multiple maternal origins traced to Asian, Middle Eastern, and European breeds rather than a single source population
- •The most recent common ancestor of Thoroughbreds lived 8,100-111,500 years ago, significantly younger than the most recent common ancestor of modern horses (0.7286 million years ago)
- •Population expansion of modern horses including Thoroughbreds occurred 5,500-11,000 years ago, coinciding with the start of domestication
- •Thoroughbred horses show no apparent correlation between geographic origin or breed and evolutionary patterns in global horse populations