Assessment of Temperature Monitoring Techniques in Neonatal and Juvenile BALB/cJ and C57BL/6J Mice (Mus musculus) as They Age.

Body temperature is an important clinical parameter in mice and can help refine humane endpoints in research models. However, due to their small size, accurate measurement of body temperature in neonatal and juvenile mice presents challenges. While rectal temperature is precise, it is invasive and stressful to both neonates and dams. Infrared technologies offer a potential alternative for assessing the body temperature of young mice. This study compared traditional rectal temperature to 3 alternative noninvasive methods: a surface probe and 2 infrared-based approaches (rodent infrared and human infrared). For each alternative method, temperature was measured at 3 different anatomic locations (dorsum, abdomen, and thorax). Temperatures were measured in mice of various ages from postnatal day (PND) 2-42. Temperature measurements were obtained in awake C57BL/6J (n = 114) and BALB/cJ (n = 113) mice to establish baseline neonatal mouse body temperature as they develop thermoregulation. Two strains of mice were used to determine whether coat color impacts infrared temperature readings. Results indicate that body temperature significantly changes as mice age for both strains. Temperatures from all 3 alternative temperature methods at all anatomic locations were significantly lower relative to rectal temperature. The surface probe had little variability among anatomic locations and closely followed the trend of the rectal thermometer with an average difference of 2.1-2.22 °C lower than rectal temperature. Of the methods assessed, the surface probe was the best alternative method to rectal temperature. These results provide valuable baseline data on normal neonatal mouse body temperature for 2 commonly used strains and suggest the surface probe could provide an alternative for body temperature measurement in young mice.