Genealogical analyses in open populations: the case of three Arab-derived Spanish horse breeds.

The research explores the genetic makeup of three Spanish horse breeds derived from Arab horses, outlining potential issues with genealogical analyses in open populations and suggesting appropriate methodologies to address these. The study used studbooks of Spanish Anglo-Arab (dAA), Hispano-Arab (dHA), and Spanish Sport Horse (dSSH) breeds along with Arab, Spanish Purebred, and Thoroughbred parental breeds to establish that the current Spanish-Arab derived populations share more genes with the Arab strains than the others.

Methodology and Data Used

• The researchers used studbooks of three Spanish Arab (SA) derived horse breeds and their parental breeds. In total, data from 211,754 horses were analysed for this study.
• For each breed (dAA, dHA, and dSSH), two genealogical analyses were performed: one using only the specific breed’s studbook data (breed exclusive dataset), and one also incorporating the genealogies from the breeds’ parental strains (completed dataset).

Analysis and Observations

• Coancestry analyses revealed that current SA-derived populations are genetically closer to Arab horses than to the other parental breeds. This indicates that these breeds retained a significant amount of Arab genes, underlining the influence of Arab horses on these breeds.
• The effective population size was calculated taking into consideration the migration rates. This resulted in equivalent closed-population effective sizes of 39.2 for dAA, 56.3 for dHA, and 114.1 for dSSH. This shows how the inclusion of immigration in population estimates can influence the effective population size.

Conclusions and Recommendations

• Using the proposed methodologies, the researchers were successful in characterising horse populations that experienced migration, providing valuable insights for future genetic and genealogical research.
• The findings underscore the importance of considering all ancestral lineages to derive reliable genealogical parameters, as incomplete genealogical data could lead to inaccuracies.
• Finally, the study examines potentially unintended consequences of selective breeding practices in open populations and discusses factors responsible for these genetic dynamics.