Fig. 2. Changes of litter mass gain during the course of 15-day lactation exposed to 23°C and 5°C. Values are means ± s.e.m. (N=8). The litter in the cold decreased mass gain from days 12 to 15, compared to that in the warm, which showed a relative constant mass gain. Different letters (a or b) above hatched bars indicate significant differences (P<0.05) in measurements within the warm group during the course of acclimation, and different letters (A, B, C) above solid bars indicate significant differences (P<0.05) within the cold-exposed group. ^***P<0.001.