# Sex-Related Differences in Show-Jumping Performance of Retired Thoroughbred Racehorses in Relation to the Interval Since Race Retirement

## TL;DR

Retired Thoroughbred racehorses, especially stallions, improve in show-jumping performance with longer transition training periods, reducing sex-related differences.

## Contribution

This study identifies the impact of transition training duration and sex on show-jumping performance in retired racehorses using Bayesian models.

## Key findings

- Stallions performed worse than mares and geldings with short transition intervals but improved significantly with longer training.
- Sex-related performance differences diminished with longer transition periods, suggesting the importance of training duration.
- Random effects like rider and horse ability explained most performance variance, highlighting the multifactorial nature of success.

## Abstract

Because racehorses retire from racing at a young age, their subsequent utilization often requires a transition to equestrian disciplines. To clarify the factors affecting this transition process, we analyzed performance in show-jumping competitions restricted to retired Thoroughbred racehorses using a Bayesian linear mixed model, focusing on the effects of horse sex and the interval between race retirement and participation in competitions (used as a proxy for the period of transition training). Stallions performed worse than mares and geldings when the interval was short. However, performance improved with longer intervals across all sexes, particularly in stallions, and clear sex-related differences diminished at longer intervals, suggesting an effect of prolonged transition training. Although the fixed effects, with the sex and interval as the primary factors, accounted for only 2–7% of the performance variance, random effects, including horse-specific ability, rider, sire, and affiliation, accounted for 40–65% of the performance variance, highlighting the multifactorial nature of success in competition. In summary, our findings suggest that a sufficiently long interval, which may correspond to the period of transition training, is important for improving jumping competition performance regardless of sex. Moreover, factors other than the interval also contributed to performance.

To investigate the factors affecting the utilization of retired Thoroughbred racehorses in equestrian disciplines, Bayesian linear mixed models were separately fitted using rank, round time, and obstacle faults from show-jumping competitions restricted to retired Thoroughbred racehorses as dependent variables, with the interaction between horse sex and the interval from race retirement to competition (as a proxy for transition training to show-jumping) as a fixed effect. When the interval was short (≤1 year), the estimated marginal mean of rank was statistically significantly lower in stallions (0.26) than in mares (0.41) and geldings (0.39). However, ranking improved with longer intervals in all sexes, with the greatest improvement observed in stallions, and the significant sex-related differences disappeared at the 3-year interval, suggesting an effect of transition training on ranking. Round time improved significantly with longer intervals in all sexes, consistent with the ranking pattern; significant improvement in obstacle faults was observed only in stallions and geldings. The explanatory power of the models, including major random effects, rider, horse ability, sire and affiliation after retirement, was moderate (conditional R2: 0.40–0.65), whereas that of the fixed effects was small (marginal R2: 0.02–0.07), indicating the multifactorial nature of success in competition.