Better hoof, better horse – genetic correlations between ability to race barefoot and performance in trotting horses.

Overview

• This study investigated how genetic factors related to the ability of trotting horses to race barefoot (without horseshoes) correlate with their racing performance.
• The researchers identified positive genetic correlations between barefoot racing ability and performance traits, suggesting barefoot capability could be a useful trait in breeding evaluations.

Background and Importance

• Harness racing is a popular sport globally, involving trotters racing while pulling a sulky.
• Racing barefoot is considered important because it can influence racing times and overall performance.
• Animal welfare concerns arise since not all horses tolerate barefoot racing well; some require shoes to protect their hooves.
• Previous studies showed moderate heritability for barefoot racing traits in two breeds: Swedish Standardbred trotters (SB) and Swedish-Norwegian Coldblooded trotters (CB), but the link to performance hadn’t been explored genetically.

Study Objectives

• Estimate genetic correlations between barefoot racing traits and performance traits in SB and CB breeds.
• Assess whether barefoot traits provide additional information useful for genetic evaluations aimed at improving racing performance and welfare.

Data and Animal Subjects

• Included horses aged 3-10 years, born between 2002-2018 (SB) and 2002-2017 (CB), with a minimum number of races: 10 for SB and 5 for CB.
• Two barefoot traits analyzed:
  • Proportion of races the horse ran barefoot.
  • Barefoot status – whether a horse raced barefoot in a given race.
• Sample sizes:
  • Proportion of barefoot races: 24,928 SB horses (724,232 observations), 4,050 CB horses (97,682 observations)
  • Barefoot status: 25,973 SB horses (875,056 observations), 3,384 CB horses (93,376 observations)
• Performance data:
  • SB: 115,185 horses aged 2-5 years (1976-2019 birth years)
  • CB: 16,360 horses aged 3-6 years (1978-2017 birth years)
  • Performance traits included best racing time per km, total earnings, placings, plus earnings per start and number of starts for SB.

Methodology

• Used bivariate mixed linear animal models to estimate:
  • Heritability of barefoot traits.
  • Genetic correlations between barefoot traits and performance traits.
  • Breeding values and annual genetic improvement rates.
• Analyses performed separately for each breed.

Key Findings

• Genetic correlations between proportion of barefoot races and performance traits were moderate and positive:
  • SB: 0.42 to 0.50
  • CB: 0.41 to 0.62
• Genetic correlations for barefoot status were more variable but generally positive:
  • SB: 0.01 to 0.63
  • CB: 0.26 to 0.59
• Proportion of barefoot races showed stronger correlations with performance than barefoot status.
• Annual genetic improvement—reflecting selective breeding progress—was higher for the proportion of barefoot races trait versus barefoot status.

Conclusions and Implications

• The ability to race barefoot is genetically linked with better racing performance in both SB and CB breeds.
• Proportion of barefoot races as a trait provides meaningful, additional genetic information beyond standard performance metrics.
• This suggests barefoot traits could be effectively included in genetic evaluation programs to improve both racing success and animal welfare.
• Findings may also be applicable to other trotter populations outside Sweden and Norway.

Significance

• Combining barefoot traits with traditional performance traits could enhance breeding strategies by:
  • Selecting for horses inherently capable of barefoot racing.
  • Potentially reducing reliance on horseshoes, which can improve welfare.
  • Optimizing race performance through a genetically informed approach.
• The study fills a previous knowledge gap regarding how hoof health and barefoot ability integrate genetically with racing success.