Thermographic assessment of surface temperature distribution and agreement between a thermographic camera, infrared thermometer, and rectal temperature in exercising horses under tropical climate conditions.

BACKGROUND AND AIM: Infrared thermography has become an increasingly valuable non-invasive imaging technique for monitoring physiological status and detecting abnormalities in horses. However, its application under tropical environmental conditions remains insufficiently investigated, particularly regarding the influence of ambient conditions on measurement accuracy and agreement with conventional temperature assessment methods. This study aimed to evaluate the agreement among a thermographic camera (TC), infrared thermometer (IR), and rectal temperature (RT), characterize body surface temperature distribution before and after exercise, and determine the effects of environmental conditions on temperature measurements in exercising horses under tropical climate conditions.

MATERIALS AND METHODS: Thirty-one clinically healthy horses performing schooling, training, or lunging exercises were enrolled in this prospective repeated-measures observational study. Temperature measurements were obtained using RT, IR at the medial canthus, and TC across the eye, neck, shoulder, back, trunk, and hindquarters regions before exercise, immediately before and after exercise, and during recovery. Environmental variables, including ambient temperature and relative humidity, were simultaneously recorded. Temperature differences among anatomical regions, exercise stages, and measurement methods were analyzed using linear mixed-effects models. Agreement between methods was assessed using Bland-Altman analysis, whereas environmental influences were evaluated using Kendall's rank correlation.

RESULTS: No significant differences were observed between the left and right body sides or among exercise activities. RT consistently recorded the highest temperatures, followed by IR and TC. Thermographic assessment demonstrated that the eye exhibited the highest surface temperature under resting conditions, whereas the back, trunk, and hindquarters showed the greatest post-exercise temperature increases (p < 0.001). Outdoor measurements produced significantly higher TC temperatures than indoor assessments (p < 0.001). IR demonstrated closer agreement with RT, with a mean difference of 1.02°C, whereas TC underestimated RT by 2.88°C and exhibited wider limits of agreement. Ambient temperature showed a strong positive correlation with TC measurements (r = 0.52, p < 0.001) but had minimal influence on IR measurements, indicating superior environmental stability of IR. Surface temperatures generally returned to baseline during the recovery period.

CONCLUSION: Thermographic imaging provides comprehensive visualization of regional surface heat distribution and effectively identifies exercise-induced thermal changes in horses under tropical conditions. However, its measurements are substantially influenced by environmental temperature and should not be used as a surrogate for core body temperature. In contrast, IR demonstrated greater agreement with RT and superior resistance to environmental variation, making it a practical alternative for rapid estimation of body temperature when rectal measurement is impractical. These findings provide valuable guidance for selecting appropriate temperature monitoring techniques for equine health assessment, exercise monitoring, and welfare management in tropical climates.