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

Research Overview

• This study examined how different water depths and the use of an active artificial river system on a water treadmill impact stress hormone levels in leisure horses during exercise.
• Researchers measured blood and salivary cortisol before, immediately after, and 30 minutes post-exercise to assess physiological stress responses.

Introduction and Purpose

• Water treadmills (WT) are commonly used for horse rehabilitation and training due to their low-impact exercise benefits.
• The purpose was to see if the depth of water and adding an active artificial river (AR) system—creating current or flow—affects stress levels in horses differently compared to dry treadmill walking.
• Stress was evaluated by measuring cortisol, a hormone released in response to physical and psychological stress.

Study Setup and Methodology

• Participants: 13 leisure horses were involved in the study.
• Exercise Regimens: Each horse completed five separate 20-minute exercise sessions:
  • Dry treadmill walking (no water)
  • Fetlock-depth water treadmill without AR
  • Fetlock-depth water treadmill with AR
  • Carpal-depth water treadmill without AR
  • Carpal-depth water treadmill with AR
• Walking speed was consistent at 1.25 meters per second across all sessions to standardize exercise intensity.
• Cortisol Sampling:
  • Blood and saliva samples were taken at three time points—before exercise, immediately after, and 30 minutes post-exercise.

Key Findings

• Blood Cortisol:
  • Increased after exercise in all conditions, confirming physical exertion induced a stress response.
  • Immediately after exercise, blood cortisol levels were significantly lower when the AR system was used, suggesting the artificial current may influence physiological stress.
• Salivary Cortisol:
  • Levels increased 30 minutes post-exercise, indicating a delayed cortisol response in saliva compared to blood.
  • The highest salivary cortisol was noted after the carpal-depth water treadmill session with the AR system, possibly reflecting increased or prolonged stress due to deeper water and current combined.
• Correlation Between Blood and Saliva Cortisol:
  • Only a weak correlation was found, likely due to different timing in cortisol appearance and transport in blood vs. saliva.
  • This suggests both types of measurements provide complementary information about stress.

Interpretation and Limitations

• The artificial river system alters physiological stress responses to water treadmill exercise, as shown by lower immediate blood cortisol and higher delayed salivary cortisol levels.
• The fixed order of exercise sessions for all horses means that the effect of the AR system is somewhat confounded with other variables such as order or novelty effects.
• Thus, while findings are preliminary, they highlight the importance of considering water flow and depth when using water treadmills for equine training and rehabilitation.
• Using both blood and saliva cortisol measurements provides a more complete picture of stress responses over time.

Practical Implications

• Water treadmill therapy can be tailored by adjusting water depth and flow to manage stress and physical load on horses during rehabilitation.
• Monitoring stress hormones helps ensure training protocols do not inadvertently increase stress.
• Trainers and veterinarians should consider both immediate and delayed cortisol responses to better assess well-being during water treadmill exercises.