One of the main advantages of equine thermography is the detection of subclinical inflammation. The present study was undertaken to determine a specific threshold value of temperature change indicative of subclinical inflammation of the lower parts of the horse's limb. The study involved monitoring 20 racehorses over a period of 10 months. Temperatures of the third metacarpal region were measured every 3 weeks, allowing the average temperature differences to be ascertained between the same areas of forelimbs from the dorsal and palmar aspects in each session. Additionally, ultrasonographic and radiographic standard examinations of lower part of forelimbs were conducted to diagnose any pathological conditions of lower forelimbs. To determine the threshold value of temperature difference the receiver operating characteristic curve method was used, based on thermographic examinations of the same measured area in 20 horses. The threshold value of temperature difference indicative of subclinical inflammation was found to be 1.25°C. In conclusion, thermography can be used as a quick and practical diagnostic tool of subclinical inflammation. These results provide additional support for the continued study of the equine thermography.