How has selection for favourable athletic traits affected inbreeding levels of the Thoroughbred?

Ryan, Aine (2022) How has selection for favourable athletic traits affected inbreeding levels of the Thoroughbred? Masters thesis, University of Gloucestershire. doi:10.46289/QBCY4076

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Abstract

Selective breeding practices have intensified in the modern Thoroughbred racing industry, where the value of precocity continues to rise. The commercialisation of athletically advanced offspring by popular sires caused a shift in breeder incentive. Selection of matings has become increasingly artificial, the effects of which may include a rise in population homogeneity and inbreeding. This study examines the pedigrees British Group 1 winners between 1970 and 2020 to seek relationships between winner breeding and elite racing performance. Data reveals moderately significant associations between the year and the percentage of linebred and inbred winners (r=-0.587; r=0.581). An increase in inbred Group 1 winners over 50 years may support the theory that modern breeder goals are driving breed homogeneity upwards. Though there is significant financial reward for producing offspring with an athletically advanced phenotype, continued artificial breeding practices may be detrimental to the longevity of the Thoroughbred. Selection is implicated in deleterious allele expression, mutational load and inbreeding depression of the Thoroughbred. Review of advanced genomic research reveals concerning prospects for the overall genomic fitness of the breed with sustained artificial selection. Though genetic purging and rescue have been shown to aid genetic recovery of other animal populations, such methods do not appear viable for the Thoroughbred because they would breach industry regulations. Further research of the impact of selection on phenotypic traits, performance and genomic viability of the breed is necessary. More evidence is required to spur changes to breeding policy that would improve the future genomic prospects of the Thoroughbred while supporting breeders.

Item Type:	Thesis (Masters)
Thesis Advisors:	Thesis Advisor Email URL Ede, Ashley UNSPECIFIED UNSPECIFIED
Additional Information:	Award conferred by the University of Gloucestershire in partnership with the Royal Agricultural University.
Subjects:	Q Science > QH Natural history > QH426 Genetics S Agriculture > SF Animal culture > SF 277 Horses
Divisions:	Schools and Research Institutes > Countryside and Community Research Institute
Depositing User:	Rhiannon Goodland
Date Deposited:	22 Oct 2026 11:57
Last Modified:	22 Oct 2026 11:58
URI:	https://eprints.glos.ac.uk/id/eprint/16603

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