Behavioral and cardiac responses to a model startle test to support the selection of retired thoroughbred racehorses for equestrian sports

Background: Equine temperament is important for equestrian activities, and behavioural traits are important selection criteria to assess if retired thoroughbred racehorses are suitable for equestrian sports or leisure riding. Scientific indicators to assist the selection of suitable retired thoroughbred horses for sport or leisure have not been previously established. Objectives: 1) to develop a procedure to assess retired thoroughbreds for their suitability for equestrian sports or leisure purposes, 2) to identify selection criteria prediciting which horses will respond positively to transition training and best suited to equestrian sports. Study design: Before-after study. Methods: Behavioural reactivity data and cardiac autonomic responses to a startle test (comprising of a plastic bag applied to the neck area) were collected from twelve retired thoroughbred racehorses, before and after transition training for equestrian sports. The twelve horses were divided into two groups, the Vigilant Group (V) and the Adaptive Group (A), based on behavioural scores assigned based on the startle test before the transition training. Results: At the test before the training, the behavioural scores and peak heart rates of the Vigilant group horses were significantly higher than those in the Adaptive group. After the training, the Adaptive group horses were assigned lower behavioural scores and demonstrated lower peak heart rates, although neither of these changes were statistically significant. The Adaptive group and the females of both groups showed significant differences in the mean rMSSD, with an increased value after training compared to before the training. The results demonstrated that the 3-month transition training was effective in reducing the horses’ responsiveness to the startle test, in both groups. Main limitations: Small number of animals was the limitation. Conclusions: We suggest that thoroughbreds retired from racing may be scientifically selected for behavioural traits suitable for equestrian sports, using peak heart rate and behavioural score parameters.