Thermoneutral Environment Improves Mouse Metabolism and Reduces Stress in Metabolic Cages

Abstract Metabolic cages MCs are frequently used to collect feces and urine samples. However, MC housing is stressful for mice and thereby potentially influences parameters of interest. We compared a standard protocol for MC housing (4 days at 23°C, including 3 days of permanent acclimatisation and 24h sampling) with a) short-term intermittent acclimatisation (3 days for 3h plus 24h MC housing), b) providing a nest (4 days at 23°C) and c) MC housing at thermoneutrality (4 days at 30°C). C57BL6/N mice were implanted with telemetric transmitters acquiring ECG, blood pressure, body core temperature, and activity. Body core temperature decreased, and heart and respiratory rates increased during MC housing at 23°C. Mice housed in MCs with a nest or at 30°C showed strongly reduced heart/respiratory rates and a higher body core temperature compared to the group housed at 23°C. Mice ate more and lost more weight when housed in MCs at 23°C in combination with a much higher brown fat activity. Torpor-like episodes were observed in male mice housed at 23°C. In addition, they had higher corticosterone levels. Our study demonstrates that MC housing at 23°C strongly influences mouse physiology and metabolism due to a substantial cold stress. Female mice seem to be less affected compared to male mice. MC housing at thermoneutrality offers a simple solution to improve animal wellbeing during MC housing. Moreover, one short-term acclimatization presumably has the same acclimatisation effect as repeated exposure to the MCs.