Salivary cortisol and eye temperature changes during endurance competitions

Area of Science:

• Equine Sports Medicine
• Animal Physiology
• Veterinary Science

Background:

• Endurance competitions present unique challenges for monitoring horse welfare and managing performance.
• Salivary cortisol (SC) and eye temperature (IRT^ET) are potential non-invasive biomarkers for assessing physiological stress in horses.
• Previous research suggests SC and IRT^ET may differ based on experience and performance outcomes.

Purpose of the Study:

• To evaluate the utility of SC and IRT^ET as biomarkers in endurance horse competitions.
• To assess their effectiveness in managing competitions and monitoring horse welfare.
• To test the hypothesis that pre-exercise SC and IRT^ET are higher in less experienced horses and post-exercise variation is higher in top finishers.

Main Methods:

• Salivary cortisol (SC) levels were measured in 61 horses across 40km and 80km qualifier rides.
• Eye temperature (IRT^ET) was measured using infrared thermography in 16 horses.
• Measurements were taken at Pre-Inspection (PI) and multiple Vet Gates (VG) to track variations from baseline.

Main Results:

• SC levels significantly increased from PI to VG1 in both 40km and 80km rides, with varied responses in subsequent gates.
• Less experienced horses in the 40km ride showed higher baseline IRT^ET at PI compared to 80km counterparts.
• Higher baseline SC at PI was linked to better placings (Top5) in the 40km race, while lower PI IRT^ET correlated with better performance in the 80km race.

Conclusions:

• Baseline IRT^ET, not SC, was higher in less experienced horses in the 40km competition.
• SC and IRT^ET provided different insights depending on the competition distance.
• Higher baseline SC correlated with better outcomes in 40km races, whereas greater IRT^ET variation indicated better performance in 80km races, suggesting distance-specific biomarker utility.