Maternal Performance in Mice at -3 degrees C: Food Consumption and Fertility

S. A. Barnett, Margaret J. Little

Abstract

Reproduction and food consumption have been studied in three classes of female A2G/Tb mice: (i) controls, kept at 21 degrees C; (ii) mice, reared in an environment at -3 degrees C, whose parents or grandparents had been transferred, as young adults, to the cold environment (new stock); (iii) old stock, of the seventeenth to nineteenth generations reared at -3 degrees C. As virgins (at 8 weeks), and also during pregnancy and lactation, both the new and the old stock at -3 degrees 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 first pregnancy, and maintained their weight better during lactation. During second lactation the old stock were much the heavier. The mice of both groups at -3 degrees C had fewer young than the controls in their first litters, and a higher mortality among their nestlings; but the old stock had a lower nestling mortality than the new. The difference between the second litters of the old and new stocks was greater: more of the former produced second 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 degrees C ate about 70% more food than controls. The increase in food consumption during pregnancy and lactation was, however, lower at -3 degrees C than at 21 degrees C, both absolutely and relative to body-weight. Old-stock females ate about the same amount of food, relative to body-weight, as those of the new stock, even during their second pregnancy and lactation, when they were more successful mothers than the new stock. The unexpectedly low consumption of food at -3 degrees 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.

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