We quantified inbreeding based on runs of homozygosity (FROH) using 333K SNP genotypes from 768 Thoroughbred horses born in North America to evaluate the effect of inbreeding on racing traits. Among North American horses, FROH was not associated (P = 0.518) with the probability of ever racing but was significantly associated with the number of race starts (P = 0.002). Among raced horses, those with a 10% higher F_ROH than the mean inbreeding coefficient were predicted to have 3.5 fewer race starts compared to horses with a mean inbreeding coefficient.

We quantified inbreeding based on runs of homozygosity (FROH) using 333K SNP genotypes from 768 Thoroughbred horses born in North America.