Fig. 1. Daily energy expenditure (DEE) as a function of body mass for lactating (filled circles, N=24) and non-reproductive (open circles, N=17) female mice exposed to 30°C. DEE was measured when the reproductive females were at day 14 of lactation. Body mass is the mean value for days 9–13 of lactation (reproductive females) or the mean value for eight consecutive days before the day of doubly labelled water (DLW) injection (non-reproductive females). The relationship for lactating females is described by y=–28.18+2.58x; the relationship for non-reproductive females failed to reach significance.