Inbreeding in the Thoroughbred horse

Area of Science:

• Animal Genetics
• Population Genetics
• Equine Science

Background:

• The Thoroughbred horse industry relies on genetic diversity for breeding.
• Understanding inbreeding trends is crucial for maintaining breed health and performance.

Purpose of the Study:

• To investigate changes in the inbreeding coefficient (F) in Thoroughbred horses over the past 45 years.
• To determine the correlation between birth year and inbreeding levels in the breed.

Main Methods:

• Genotyping of 467 Thoroughbred horses born between 1961 and 2006.
• Utilizing the Illumina Equine SNP50 bead chip with 54,602 single nucleotide polymorphisms (SNPs).
• Estimating the Spearman rank correlation coefficient (r) between birth year and inbreeding coefficients.

Main Results:

• Inbreeding in Thoroughbreds has increased over the past 40 years.
• A significant, though weak, positive correlation (r = 0.24, P < 0.001) was found between birth year and inbreeding.
• The majority of inbreeding increase occurred post-1996, coinciding with increased stallion usage.

Conclusions:

• Inbreeding in Thoroughbred horses is a growing concern.
• The trend suggests a potential impact of modern breeding practices, such as increased stallion coverage, on genetic diversity.
• Further research is warranted to explore the long-term implications for the breed.