Equine Blood and Salivary Cortisol Levels While Exercising on a Water Treadmill with an Artificial River System

A water treadmill (WT) is used in equine rehabilitation and training. This study aimed to investigate whether varying water depths and using an active artificial river (AR) system during water treadmill exercise would affect physiological stress responses in leisure horses. Thirteen leisure horses participated in five 20 min WT sessions, including those with a treadmill with dry belt, fetlock-depth WT (with/without AR), and carpal-depth WT (with/without AR) at a walking speed of 1.25 m/s. Blood and salivary cortisol levels were measured before, immediately after, and 30 min after exercise. Blood cortisol levels increased after exercise in all sessions. Immediately after exercise, blood cortisol concentrations were significantly lower following the AR sessions. Salivary cortisol concentrations increased 30 min after exercise, with the highest values observed following the carpal-depth WT + AR session. The weak blood-salivary cortisol correlation likely reflects differences in temporal kinetics and biological matrices. Because all horses completed the experimental sessions in the same predefined order, the effects of AR mode cannot be completely separated from all other uncontrolled effects. However, these preliminary findings indicate that activation of the AR system modifies physiological responses during water treadmill exercise and highlight the importance of combining blood and salivary cortisol measurements when evaluating equine responses to exercise.