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.