Abstract: Body temperature is one of the important physiological indicators for the health status during sheep breeding. Therefore, it is often required for the high accuracy and long service life of the temperature measurement devices. However, the existing ear tags have limited the reliable monitoring data and the high efficiency of breeding. In this study, the temperature accuracy of the low-power Bluetooth ear tags was improved in the sheep breeding scenario. A low-power Bluetooth system and chip were introduced as the microcontroller of the ear tag. The power consumption and performance were improved in the hardware design, compared with the conventional Bluetooth. The size of the ear tag was considered and then computed for the capacity using the conventional constant current source-driven dual AD circuit. A voltage-driven dual AD circuit was improved after optimization. An AD1 reference source circuit was added to achieve a dual AD synchronous sampling circuit architecture. The errors were reduced under the circuit heating, environmental temperature, and power supply voltage fluctuations; At the same time, the errors were also reduced from the circuit signal noise and common-mode voltage. Furthermore, the signal conditioning unit was introduced to effectively suppress the power supply fluctuations and common-mode interference; A crescent-shaped design was adopted for the printed circuit board (PCB) of the ear tag. The 33% of the space was saved after the addition, compared with the conventional square or circular design. In terms of the thermal conduction structure, the 0.5-mm high-purity electronic-grade copper was selected as the thermal conduction base of the ear ring label, rather than the conventional probe design. The contact surface was designed on the side where the earring label contacted the ear, according to the internal shape of the sheep's ear. The contact area greatly improved the thermal conduction, while the contact thermal resistance was reduced after design. An intermittent working mode was designed with a temperature measurement frequency of once per minute and a transmission frequency of once every ten minutes, according to the temperature variation in the sheep. The energy consumption of the equipment was significantly reduced under this mode. Temperature calibration was realized using the temperature of sheep. The temperature segmentation was optimized to set the upper and lower limits of the temperature measurement to 35°C to 45°C. The uniform sampling points were selected for the body measurement. The Murata NCP18WF104 thermistor was calibrated within the temperature range. A constant temperature water bath and ammonia heating tube were provided for a stable environment at a constant temperature. A fluke 1595 and 6015T was utilized to measure the thermistor and unqualified platinum resistors. The Hogg and Stan-Hart equation was compared to select the best-fitting fourth-order Stan-Hart equation. A high-precision thermistor-temperature conversion model was established to perform the linear fitting on the measurement. The fitting error was less than 0.1°C under experimental conditions. A field test was carried out to verify the ear tags. Actual tests were conducted in 4 sheep sheds at the Feimenyuan Farm in Hefei City, Anhui Province, China. A three-day temperature test was performed on the 126 sheep for the stability of the ear tag. The experimental results show that the temperature error of the ear tag was controlled within ±0.2°C, the data transmission rate exceeded 95.3%, and the equipment service life was extended by approximately 1-1.5 years. The performance indicators of the wearable body temperature monitoring devices were improved after collaborative optimization of the hardware, structure, working mode, and temperature calibration. The finding can also provide reliable technical support for the precise health monitoring in intelligent agriculture.