Genetic parameter estimates of performance traits in Iranian Thoroughbred race horses using a Bayesian approach.

Overview

• This study estimated the genetic influence on key performance traits of Iranian Thoroughbred racehorses using a Bayesian statistical approach to inform breeding strategies.

Background and Importance

• Thoroughbred racehorse performance depends on both genetic factors (inherited traits) and environmental factors (training, management, race conditions).
• Understanding the genetic parameters—such as heritability and genetic trends—helps in designing selective breeding programs to improve performance traits.
• The study focused on traits related to race performance:
  • Race Completion Time (RCT) – how quickly a horse finishes the race.
  • Rank at the End of Competition (REC) – the finishing position or rank in a race.
  • Average Speed (AS) – the average speed of the horse during the race.

Data and Methods

• Performance data collected from the Iranian Equestrian Federation spanning 2002-2021.
• Pedigree data covered 14,391 individual racehorses to establish familial relationships relevant for genetic analysis.
• Tools and Analysis:
  • CFC software was used for pedigree data processing.
  • Bayesian inference was applied:
    • Gibbs sampling with the ‘gibbs1f90’ program was applied for continuous traits (RCT and AS).
    • ‘thrgibbs1f90’ was used for the categorical trait (REC).

Results: Heritability Estimates

• Heritability refers to the proportion of observed variation in a trait that can be attributed to genetic differences.
  • RCT (Race Completion Time): Moderate heritability at 0.25, meaning about 25% of variation in race time is genetic.
  • AS (Average Speed): Moderate heritability of 0.23, showing average speed is similarly influenced by genetics.
  • REC (Rank): Low heritability at 0.09, indicating most variation is due to environmental or non-genetic factors.
• Rider identity and race-specific factors (date and city of race) had significant effects on RCT and AS, highlighting environmental influences.

Results: Genetic and Phenotypic Trends

• Genetic trends refer to changes in the genetic merit of the population over time, independent of environmental effects.
• Findings:
  • RCT showed an unfavorable genetic trend: it increased by 0.15 seconds per year (p = 0.02), meaning genetically horses are getting slower over time.
  • AS showed a significant decline of 0.02 meters/second per year (p = 0.0001), also an unfavorable genetic trend indicating slower genetically determined speed.
  • REC genetic trend was negligible (-0.0004; p = 0.94), indicating no genetic improvement in race ranking.
  • Phenotypic trends (total observed changes in performance) did not match genetic trends, suggesting environmental factors might be compensating for the genetic decline in RCT and AS.

Conclusions and Implications

• The study highlights that RCT and AS have sufficient genetic basis to respond to selective breeding.
• The low heritability of REC suggests environmental management plays a larger role in finishing rank than genetics.
• The unfavorable genetic trends in RCT and AS suggest that the current breeding programs may not be effective or could even be selecting against desired performance genetically.
• Stable or improving phenotypic performance despite negative genetic trends likely reflects improvements in management, training, or race conditions masking genetic setbacks.
• There is a critical need to revise and optimize breeding strategies to ensure long-term genetic improvement rather than relying solely on environmental enhancements.
• Overall, genetic evaluation using Bayesian methods provides valuable insights supporting data-driven decisions for enhancing the genetic quality of Iranian Thoroughbred racehorses.