Maternal performance in mice at –3°C: food consumption and fertility

Abstract

Reproduction and food consumption have been studied in 3 classes of female A2G/Tb mice: (i) controls, kept at 21[degree]C; (ii) mice, reared in an environment at -3[degree]C, whose parents or grandparents had been transferred, as young adults, to the cold environment (new stock); (iii) old stock, of the 17th to 19th generations reared at -3[degree]C. As virgins (at 8 weeks), and also during pregnancy and lactation, both the new and the old stock at -3[degree]C were lighter than the controls. As virgins, the old-stock females were about the same weight as the new; but they put on more weight during their 1st pregnancy, and maintained their weight better during lactation. During 2nd lactation the old stock were much the heavier. The mice of both groups at -3[degree]C had fewer young than the controls in their 1st litters, and a higher mortality among their nestlings; but the old stock had a lower nestling mortality than the new. The difference between the 2nd litters of the old and new stocks were greater: more of the former produced 2nd litters; the number born in old-stock litters was higher; and mortality was again lower. Relative to body-weight, the virgin females of both stocks at -3[degree]C ate about 70% more food than controls. The increase in food consumption during pregnancy and lactation was, however, lower at -3[degree]C than at 21[degree]C, both absolutely and relative to body-weight. Old-stock females ate about the same amount of food, relative body-weight, as those of the new stock, even during their 2nd pregnancy and lactation, when they were more successful mothers than the new stock. The unexpectedly low consumption of food at -3[degree]C may be related to (a) reduced activity in the cold, (b) superior metabolic efficiency. In addition, the old-stock mice, females and young, probably utilize food more efficiently than the new stock.