Quantifying the instability of core temperature in rodents

Radiotelemetry provides researchers with the ability to sample the core temperature of rodents and other species rapidly. Compared to large mammals, the time-course of core temperature of rodents is variable and their data are often averaged into bins of one or more hours for publication. When viewing averaged data, a stable core temperature over a wide range of ambient temperatures is observed; however, if the time-course of core temperature of individual animals is examined closely with a sampling period of 1–10 min, a continuous waxing and waning of temperature is observed. It is proposed that calculating the change in temperature from one time point to the next (i.e., temperature differential) is an informative measure of the performance of the thermoregulatory system. A quantitative measure of the stability of the thermoregulatory system can be determined by calculating the absolute value of the temperature differential. It is shown that the absolute temperature differential (ATD) is dependent on ambient temperature, genetic strain, type of cage bedding, and body size. The ATD is simple to calculate from telemetry data and may be an important parameter for the study of rodent thermal physiology.