Eye surface infrared thermography usefulness as a noninvasive method of measuring stress response in sheep during shearing: correlations with serum cortisol and rectal temperature values

• Infrared thermography of 3 eye regions (lateral canthus, central cornea, medial canthus) was obtained. • Higher cortisol values, rectal, entire eye and medial canthus temperatures are found after shearing in sheep. • Rectal temperature was positively correlated with medial canthus both before and after shearing. • Positive correlation between cortisol, rectal and medial canthus is found after shearing in sheep. • Eye infrared thermography usefulness as an immediate and non-invasive physiological tool to assess stress response in sheep is proposed. During shearing, animals’ welfare is adversely affected and acute stress occurs. Once animal perceives a threat, it develops behavioral, autonomic, endocrine or immune responses to maintain homeostasis. This study aimed to investigate the usefulness of eye temperature assessment by infrared thermography (IRT) to evaluate acute stress response in sheep undergoing a shearing procedure. From each animal, blood sampling, rectal and eye temperature assessment were performed before shearing (T PRE ), 5 (T POST5 ) and 60 (T POST60 ) minutes after the end of shearing procedure. On blood samples the serum cortisol concentrations were evaluated. Rectal temperature (T RECTAL ) was measured using a digital thermometer. Thermographic acquisitions of eye temperature were performed from the eye total area (T EYE ) and from three regions of interest (lateral canthus, T ROI-1 ; central cornea, T ROI-2 ; medial canthus, T ROI-3 ). One-way analysis of variance showed a significant increase of serum cortisol concentration, T RECTAL , T EYE and T ROI-3 ( p < 0.001). Serum cortisol was positively correlated with T RECTAL and T ROI-3 at T POST5 and T POST60 . T RECTAL resulted positively correlated with T ROI-3 at T PRE , T POST5 and T POST60 . Agreement between T RECTAL and each eye temperature considered (T EYE , T ROI-1 , T ROI-2 , T ROI-3 ) has been shown by Bland–Altman plots at each time point of monitoring period. The findings obtained in the current survey suggest that the medial canthus is the most suitable region for eye temperature measurement to asses stress response in animals. Moreover, this study highlighted the usefulness of IRT as an immediate and non-invasive physiological measure to assess stress response in sheep.