Eye Temperature Measured with Infrared Thermography to Assess Stress Responses to Road Transport in Horses

Abstract

The aim of the present study was to investigate eye temperature modifications after road transport in athletic horses habituated to travel. Eight adult Italian saddle horses traveled 100 km and, two weeks later, 300 km. Eye temperature (ET), rectal temperature (RT) and serum cortisol concentration were assessed before (T1), after (T2) and 60 min (T3) after the road transport. ET was evaluated with infrared thermography (IRT) in three regions of interest: EL1 (medial canthus), EL2 (central cornea) and EL3 (lateral canthus). Two-way analysis of variance (ANOVA) for repeated measures showed statistically higher values at T2 and T3 for EL1 (p < 0.01), EL2 (p < 0.01) and EL3 (p < 0.01) following the 100 km journey. RT (p < 0.01) showed higher values at T2 and T3 after the 100 km journey and higher values at T2 (p < 0.01) following the 300 km journey. ET values were positively correlated with RT at T1, T2 and T3 following the 100 km journey and at T2 following the 300 km journey and positively correlated with serum cortisol concentration at T1, T2 and T3 following the 100 km journey and at T2 and T3 following the 300 km journey. Eye temperature monitoring with IRT allows quick and practical strategies to monitor an animal's physiological state and welfare during daily activities.

Keywords: cortisol; eye temperature; homeostasis; horse; rectal temperature; road transport.

Figure 1

Representative left and right eye with the selected ROIs (EL1 (medial canthus), EL2 (central cornea) and EL3 (lateral canthus)) and the obtained temperatures EL1_max, EL1_avg and EL1_min, EL2_max, EL2_avg and EL2_min and EL3_max, EL3_avg and EL3_min in a horse.

Figure 2

Coefficients of correlation (r) among the values of eye temperature (EL1_avg chosen as a representative area) [45], rectal temperature (RT) and cortisol concentration, expressed in their conventional unit of measurement, in horses before (T1), after (T2) and 60 min (T3) following journeys of 100 and 300 km. Blue dots represent RT, and red dots represent cortisol concentration. Bottom right: the r coefficient refers to the correlation between ET and RT; bottom right refers to the correlation between ET and cortisol concentration. At the top right-hand side, the value of r refers to the correlation between RT and cortisol concentration. Symbol * corresponds to p < 0.01. Symbol ** corresponds to p < 0.001. Symbol *** corresponds to p < 0.0001.