Salivary Cortisol and Infrared Thermographic Ocular Temperature Use as Biomarkers during Endurance Competitions

Abstract Objective quantification of effort and distress during endurance rides through biomarkers could help manage competitions more effectively and monitor horse welfare through an evidence-based approach. This study aimed to determine if salivary cortisol (SC) and ocular temperature measured by infrared thermography (IRTOT) are related to the outcome in endurance competitions. Saliva was collected and IRTOT measured from 61 and 14 horses, respectively, competing at qualifier 40km and 80km rides at Pre-Inspection (PI) and Vet Gates (VG). The variation of the baseline SC at the PI (median±IQR=0.27ng/dl±0.36) into VG1 was abrupt (93-256% rise) and in the next VGs either decreased or rose at a very modest level. Less experienced horses in the 40km ride showed a significantly (p<0.05) higher IRTOT (median±IQR=35.7ºC±1.4) at the PI, than their counterparts in the 80Km ride (median±IQR=35. ºC ±1.5). Horses classifying in the Top5, in the 40 km ride category had significantly (p=0.05) higher SC levels (median±IQR=0.90ng/ml ±0.61) at the PI, than horses positioned from 10th position on (median±IQR = 0.16ng/ml ±0.40). A lower IRTOT in the PI was correlated with a better placement (p>0.05) and those in the Top5 (median±IQR = 33.9ºC ±0.0) had a higher variation (+10.65%) into the last VG. A 62% predictive value for elimination (80% sensibility and 82% specificity) where SC is higher than 0.23ng/ml is advanced. SC and IRTOT can be potentially used in association to characterise physical effort and emotional stress in endurance competitions, but its significance to performance has to be put in context with the competition level.