The technology concerns a continuous body temperature measuring system. This system is based on measuring the maximum temperature of the dairy cow´s eye using infrared thermography. There is a positive correlation between eye temperature and internal (rectal) temperature. The change in eye temperature essentially replicates the internal body temperature, and thus internal temperature conditions can be detected. Knowledge of the initial increase in body temperature provides crucial information for a quick start of possible treatment. Early detection of the onset of a febrile illness will help to significantly increase the economy of breeding by, above all, reducing the amount of medicines needed and improving the overall health and thus the welfare of farmed animals.