The Thoroughbred Theory: Influence of Breed on Performance at the CCI5*-L Level of Eventing.

Breed bias exists within many of the top disciplines of equestrian sport. Therefore, the objective of this study was to evaluate the influence of breed on performance at the CCI5*-L level of eventing. To do so, the results of all CCI5*-L events from 2014 to 2024 were assessed. Initially, Thoroughbreds were compared to all non-Thoroughbreds, and this was followed by assessing the ten primary breeds. Data included penalties accrued in dressage, cross country, show jumping, and overall. Additionally, the likelihood of completing each phase was assessed. It was found that Thoroughbreds accrued more dressage penalties than non-Thoroughbreds ( < 0.001). When comparing primary breeds, Thoroughbreds were found to accumulate more dressage penalties than Hannoverian, Irish Sport Horse, Dutch Warmblood, Oldenburg, and Selle Francais ( < 0.03). When assessing cross-country, Thoroughbreds were more likely to finish without fault when compared to non-Thoroughbreds ( < 0.001). Non-Thoroughbreds were more likely to show jump without fault ( < 0.001), while Thoroughbred were found to have higher overall show jumping penalties in comparison to Anglo-European Studbook, Holsteiner, Irish Sport Horse, Dutch Warmblood, Oldenburg, and Selle Francais ( = 0.01). When evaluating overall penalties accumulated throughout the event, there was no effect of breed ( = 0.42). Overall, there was no advantage in competing a non-Thoroughbred in comparison to a Thoroughbred when considering total penalties accrued, indicating a level playing field within competition. Therefore, breed bias against TBs should be negated when selecting for CCI5*-L eventing prospects.