No-Contact Microchip Monitoring of Body Temperature in Yearling Horses

In clinics, temperature is used as an indicator of health. Mostly rectal temperature is recorded, requiring handling and time. Temperature-sensitive identification microchips could be an alternative. Foals (26 males and 17 females), 4–12 months old, were housed in stalls over two winters (December–February). They were equipped with an identification and temperature sensor microchip implanted in the neckline. Temperature was recorded using an antenna located near the drinking trough. Animals were fed concentrated feed and forage twice daily, with free access to water. Rectal temperatures (79 measurements) were recorded simultaneously in 26 animals. Data were analyzed with a linear mixed model, using natural cubic splines for the mean curve and a random horse effect. All animals remained healthy throughout the study. More than 100,000 recordings were obtained. Mean temperature for all individuals at all times was 37.5 ± 0.1°C. Time of the day affected temperature with a daily amplitude of 0.96°C (P < .001). Lowest temperatures were observed before dawn, the acrophase occurring around 18:00, with a smaller increase around midday. Mean temperature was 0.26°C higher in males (P < .05). It was also 0.1°C higher in light (<200 kg) compared with heavier foals (P < .001). Temperature decreased with increasing daylight (−0.35°C over the study period, P < .001). Microchip and rectal temperatures remained within normal limits and were significantly correlated (R² = 0.16, P < .001). This noninvasive tool does not require extra-handling and will allow a better monitoring of normal body temperature values taking into consideration time of the day, meal time, and sex.