Infrared thermography as indicator of physical effort in horses

The aim of this study was to assess the use of infrared thermography as an indicator of physical effort in horses. The respiratory rate (RR) and infrared thermography images (IRT) of the eye, ear and mouth were measured in sixteen crossbreed horses used for livestock ranch work. The assessments were carried out always between 17 and 18 h and under two conditions carried out in two consecutive days: (i) the pre-exercise condition, measuring RR and taking the IRT pictures after a resting period of at least 12 hours; and (ii) the after a working day condition, assessing the same variables after a regular working day. The air temperature (AT) and humidity (RAH) were measured. The variables were analyzed using factor analysis with varimax rotation. The first two factors explained 69.71% of the total variability of the data set. The first factor, named pre-exercise, explained 47.04% of the total variability and showed that higher AT and lower RAH were associated to higher temperatures (IRT) in the eye, ear and mouth at the pre-exercise condition. The second factor, named post-exercise, explained 22.67% of the remaining variability, showing that greater temperatures (IRT) in eye, ear and mouth after the day work were associated to higher RR at the end of work. These results indicate that the pre-exercise IRTs were related to the thermal conditions of the environment and that the post-exercise IRTs were associated to the physiological response of horses to physical effort; indicating that IRT of yes, ear and mouth have potential to be used as indicator of physical fitness in horses. This non-invasive, quick and easy to employ tool could be used to evaluate the welfare of horses during ranch work. However, more studies are needed, including other parameters to better understand the effectiveness of infrared thermography as horse welfare indicator.