Salivary cortisol and eye temperature changes during endurance competitions.

Abstract

BACKGROUND: The purpose of this study was to investigate the usefulness of salivary cortisol (SC) and eye temperature measured by infrared thermography (IRT) as biomarkers to manage competitions more effectively and monitor horse welfare in endurance competitions. Based on previous studies, it was hypothesised that pre-exercise baseline SC and IRTwould be higher in younger or less experienced horses, and that post-exercise variation from baseline would be higher in the top finishers. RESULTS: Salivary cortisol measured in 61 competing at qualifier 40&#x2009;km and 80&#x2009;km rides showed an abrupt variation (93-256% rise) of the baseline SC levels [median&#x2009;&#xb1;&#x2009;interquartile range (IQR)&#x2009;=&#x2009;0.27&#x2009;ng/dl&#x2009;&#xb1;&#x2009;0.36] obtained at the Pre-Inspection (PI) into Vet Gate (VG)1 independently of the covered distance, but modest or even lower in the subsequent Vet Gates, e.g. VG2 or VG3. The IRTmeasured concomitantly in 16 horses showed significant (p&#x2009;<&#x2009;0.05) higher levels at the PI in less experienced horses participating in the 40&#x2009;km ride (median&#x2009;&#xb1;&#x2009;IQR&#x2009;=&#x2009;35.7&#x2009;&#xb0;C&#x2009;&#xb1;&#x2009;1.4) than their counterparts in the 80&#x2009;km ride (median&#x2009;&#xb1;&#x2009;IQR&#x2009;=&#x2009;35.0&#x2009;&#xb0;C&#x2009;&#xb1;&#x2009;1.5), but not SC. Baseline SC levels at the PI of horses classifying in the Top5 in the 40&#x2009;km ride category were significantly (p&#x2009;<&#x2009;0.05) higher median&#x2009;&#xb1;&#x2009;IQR&#x2009;=&#x2009;0.90&#x2009;ng/ml &#xb1;0.61) when compared to horses positioned from 10th position on (median&#x2009;&#xb1;&#x2009;IQR&#x2009;=&#x2009;0.16&#x2009;ng/ml &#xb1;0.40). A lower IRTin the PI was correlated with better placement (p&#x2009;<&#x2009;0.05) and those in the Top5 (median&#x2009;&#xb1;&#x2009;IQR&#x2009;=&#x2009;33.9&#x2009;&#xb0;C&#x2009;&#xb1;&#x2009;0.0) had a significantly (p&#x2009;<&#x2009;0.5) higher variation (+&#x2009;10.65%) into the last VG. CONCLUSION: Pre-exercise baseline IRTlevels, but not SC, were higher in less experienced horses in the 40 compared to their counterparts in the 80&#x2009;km ride competitions. SC and IRTshowed different indications according to the competition. In the40&#x2009;km ride competition, higher baseline pre-exercise SC levels seemed to be linked to a better classification outcome. In contrast, in the 80&#x2009;km ride horses, the higher IRTvariation from pre-exercise into final Vet Gate was the parameter associated with a better performance. A more controlled environment and a larger sample are needed to confirm these results and monitor horse welfare in competitions.