Analysis of the Pedigree and Ancestors of the Cutting Population of the Quarter Horse Breed.
Authors: Yahagi Rodrigues Larissa, da Silva Faria Ricardo António, de Vasconcelos Silva Josineudson Augusto Ii
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Researchers analysed pedigree records spanning nearly two centuries to assess genetic diversity within the Brazilian Quarter Horse cutting population, examining 1,590 elite competition horses and their 5,832 ancestors born since 1834. Despite low inbreeding coefficients (1.98%) and acceptable relatedness measures, the effective population size was just 136 animals, revealing a critically narrow genetic base underpinning the competitive population. Just five stallions—Doc Bar, Peppy San Badger, Freckles Playboy, Poco Lena, and High Brow Cat—accounted for nearly 31% of the population's genetic contribution, with only 37 effective ancestors (rather than the 899 registered ancestors) explaining the true genetic diversity. This pronounced reliance on a small number of foundational sires presents significant long-term risks for genetic resilience, disease susceptibility, and the population's capacity to adapt to evolving performance demands. Practitioners should counsel breeders toward strategic outcrossing with genetically distinct lineages and broader use of available sires to counteract the narrowing genetic base, particularly given that deliberate mate selection could substantially improve population health without sacrificing cutting ability.
Read the full abstract on PubMed
Practical Takeaways
- •Breeding programs should prioritize introducing genetic material from underutilized ancestors outside the top 5 to expand the genetic base and reduce future inbreeding risk
- •Current cutting horse genetics are heavily dependent on a small ancestral pool; breeders need directed mating strategies that deliberately cross lineages from different ancestral origins
- •Monitor future generations closely for recessive genetic disorders, as the narrow effective population size and founder genome numbers increase risk of genetic disease accumulation
Key Findings
- •Effective population size was only 136 animals despite 1,590 elite horses studied, indicating genetic bottleneck in Brazilian cutting Quarter Horses
- •Just 10 ancestors explained 39.2% of genetic diversity, with the top 5 ancestors (Doc Bar, Peppy San Badger, Freckles Playboy, Poco Lena, High Brow Cat) accounting for 30.7% of marginal genetic contributions
- •Low inbreeding coefficient (1.98%) and relatedness coefficient (2.18%) despite narrow genetic base, suggesting recent diversification from limited founders
- •Only 37 effective ancestors and 23 effective founder genomes were responsible for the entire population, indicating severe narrowing of the initial genetic base