In this study, therapeutic riding horses (TRH) and jumping horses (JH) were exposed to acute, novel stressors to objectively measure individual reactivity and chronic stress. The responses of TRH and JH were compared when exposed to a restraint and startling stimulus. The restraint involved covering the horse’s head with a hood for one hour, and the startling stimulus (40 cm long red and white synthetic holiday garland shaken with a rustling noise inside the box). During the challenges, horses spent most of their time immobile. During the challenges, a higher average basal HR was found in TRHs compared to JH. During the restraint, average heart rate during pawing was higher than during other behaviours. Lymphocytes decreased in samples taken after the removal of the hood. Overall, there were no differences between TRHs and JHs in their reactions to novel stimuli.