Investigating Eye Temperature as a Potential Biomarker for Emotion in Thoroughbred Horses

This study investigated whether differences in eye temperature could be detected in Thoroughbred horses exposed to two different training conditions: either high or low probability of receiving a food reward. Twenty-three horses were trained to complete a simple industry relevant task. During the high probability scenario horses received a food reward in 70% of the trials (n=10) for performing the correct response, whilst horses in the low probability scenario only received a reward in 30% of the trials. Eye temperature was recorded across various sampling points. The study hypothesised that the ET of Thoroughbred horses would differ significantly between the scenarios, potentially reflecting changes in their inferred emotional states. Results indicated that the ET of horses in the low probability scenario significantly decreased (p < 0.005), whilst the ET of horses in the high predictability scenario showed no significant changes. Whilst changes in ET were detected, they cannot be interpreted as emotion, as they are more likely explained by changes in blood to the orbital region caused by mastication.