The climate of the earth is expected to change rapidly and continuously. Despite climate change is expected to impact on productivity of crop and livestock, a study for adaptation and impact of livestock to global warming is not enough. This study was performed to develop a method to evaluate the effects of heat stress on dairy cattle. Feedlot environment and health status of livestock were measured through an infrared thermography camera and a temperature-humidity sensor. Environmental factors such as temperature and humidity were measured to calculate the Temperature humidity index (THI). The change of the milk yield was similar to THI data pattern, suggesting that THI might play an important role to predict the effect of climate change on dairy cattle. THI data would be useful to predict long-term climate change effects on dairy cattle with RCP8.5 scenario.