Mice at lower ambient temperatures require increased rates of metabolism and thermogenesis. The normal core body temperature of mice is approximately 37°C (green line), as for most mammals. Mice housed at their thermoneutral temperature (~30°C, TT, red dashed line) are able to meet this temperature using only their basal metabolic rate (BMR) for heat production (red arrow). Mice housed under standard temperature conditions (~22°C, ST, red dashed line) cannot rely solely on their BMR, and thus a number of adaptive thermogenic pathways are turned on to maintain normal body temperature (yellow arrow).