Subcutaneous temperature monitoring through ear tag for heat stress detection in dairy cows

Heat stress remains one of the greatest threats to the economic viability of the dairy industry. The threat becomes even greater during warm and humid conditions, especially for those larger farms seeking to expand their operations. This study sought to develop and test a reliable and timely method that allows dairy farmers to monitor the body temperatures of their animals, using a compact, lightweight ear tag device, including a wirelessly rechargeable battery. The device is also capable of wirelessly transmitting a cow's subcutaneous temperature in real-time by means of an injectable, passive RFID biosensor. The outcomes showed that subcutaneous ear-base temperature (EBT) can synchronously follow the core body temperature (CBT) while also producing a comparable temperature gradient. That is, on average, the difference between a CBT and an EBT is 0.68 ± 0.35 °C. Based on regression models, the CBT of a cow can be accurately predicted based on EBT, with an average error of around 0.20 °C and as low as 0.11 °C by using a multivariate polynomial regression model, which includes external environmental conditions as well as the cow's health information, including milk production. The outcomes indicate that there is a consistent, predictable time lag between increases in microenvironmental conditions and increases in a cow's body temperature. These findings should enable dairy barn designers to develop and employ automated control-loop systems that utilise physiological feedback to improve management practices aimed at detecting heat stress and mitigating its effects in a timely manner, while minimising energy use. •An ear tag device was developed to transmit body temperature wirelessly in real time.•The subcutaneous ear base temperature readings were accurate under heat stress conditions.•There were time-consistent lags between the environmental THI rise and the body temperature increase.•A regression model based on subcutaneous temperature could accurately predict core body temperature.