Monitoring of the core body temperature of cows using implantable wireless thermometers

Monitoring of cattle body temperature is useful for the detection of estrus, prediction of parturition, and maintenance of health. Recently, methods of monitoring body temperature in sites including the rumen, vagina, skin surface, and subcutis, have been studied. However, these methods are associated with limitations, such as loss of a device and the induction of stress. In addition, these studies did not consider differences among the measurement sites. In the present study, we developed implantable wireless thermometers and implanted them into a cow in 10 different anatomical locations. We then investigated the relationships among the temperatures recorded at these locations and rectal temperature (RT). The temperatures in three endoceliac and seven subcutaneous locations were monitored and compared over 6 weeks during winter. The temperatures in the abdominal cavity and inner flank wall correlated strongly with RT (r = 0.74 and 0.76, respectively). Of the subcutaneous locations, the tail-base (TB) was associated with a high reception rate for wireless transmission (97.6%) and the temperatures at this location also correlated well with RT (r = 0.62). These results indicate that the implantable wireless thermometer can continuously monitor core body temperature over a long period. Endoceliac sites and the TB are good candidates for bovine temperature monitoring. In addition, we were able to predict body temperatures that strongly correlated with the temperatures at endoceliac sites using machine learning and inputs of subcutaneous and ambient temperatures. The correlation coefficients were 0.93 when seven subcutaneous temperatures were used, and 0.77 when two were used. These results suggest that long-term monitoring of core body temperature would be possible using a wireless thermometer implanted in a subcutaneous location.