Salivary cortisol and eye temperature changes during endurance competitions.
Authors: de Mira Monica C, Lamy Elsa, Santos Rute, Williams Jane, Pinto Mafalda Vaz, Martins Pedro S, Rodrigues Patrícia, Marlin David
Journal: BMC veterinary research
Summary
# Editorial Summary Researchers measured salivary cortisol and infrared eye temperature in 61 endurance horses competing in 40 km and 80 km qualifier rides to determine whether these stress biomarkers could help officials manage competitions and safeguard welfare. Both markers showed substantial changes during competition—cortisol levels spiked dramatically (93–256%) immediately after the first phase before moderating at subsequent veterinary gates, whilst eye temperature patterns differed notably between less experienced horses in the shorter distance (35.7°C) and their more experienced counterparts (35.0°C). The findings revealed unexpected complexity: in 40 km rides, horses finishing in the top five had significantly higher baseline cortisol at pre-inspection (0.90 ng/ml) compared to those placing 10th or lower (0.16 ng/ml), whereas in 80 km rides, greater eye temperature *increase* from start to final veterinary gate (not baseline temperature) correlated with better performance. For practitioners managing endurance athletes, these results suggest that neither biomarker alone reliably predicts performance or welfare across all competition distances, and that different physiological profiles may characterise success depending on the demands of 40 km versus 80 km efforts—though the authors acknowledge that larger, more controlled studies are needed before these measures can be confidently applied to competition monitoring protocols.
Read the full abstract on PubMed
Practical Takeaways
- •Salivary cortisol and eye temperature may serve as useful welfare monitoring tools during endurance competitions, but their interpretation differs between 40 km and 80 km distances
- •Baseline eye temperature can help identify less experienced horses who may need closer monitoring, particularly in shorter rides
- •Higher pre-competition cortisol in top performers during 40 km rides suggests arousal/readiness may differ from fatigue; interpret cortisol changes contextually throughout competition
Key Findings
- •Salivary cortisol increased 93-256% from baseline to first vet gate, independent of distance, then remained modest or decreased at subsequent vet gates
- •Less experienced horses in 40 km rides showed significantly higher baseline eye temperature (35.7°C) compared to 80 km riders (35.0°C)
- •Top 5 finishers in 40 km rides had significantly higher baseline cortisol (0.90 ng/ml) versus 10th place and beyond (0.16 ng/ml)
- •Lower pre-exercise eye temperature correlated with better placement; top finishers showed 10.65% temperature increase to final vet gate