Effects of reduced food intake on reproduction in mice.

The effect of undernutrition on the reproductive performance of the Quackenbush strain of mice was studied using four dietary levels: ad libitum (8.0 g per mouse per day; D100), 85% (D85), 70% (D70), and 55% (D55) of ad libitum food intake. Dietary restriction for 60 days at the 55% level resulted in an increase in the length of the oestrous cycle compared with other dietary levels, whereas D85 and D70 mice did not differ from the control group. When the underfed mice were fed ad libitum their reproductive performance did not differ from that of the D100 mice. In a second experiment mice were fed the restricted diet for 2 weeks before males were introduced. The males were fed ad libitum except for a 5-day mating period, when they were removed and replaced by another group of males. On days 1, 7, and 16 of pregnancy approximatley 10 mice per dietary level were killed and the ovulation rate, implantation rate, and late embryonic survival were estimated. The remainder of the mice were allowed to litter for studies of the litter size, birth weight and sex ratio. Dietary restriction did not affect the ovulation rate and only 45% restriction resulted in a decreased implantation rate. The late embryonic survival was reduced at all levels of restricted food intake, but sex ratios were unaffected by dietary intake. Dietary restriction of 30% and 45% decreased the littering rate and increased foetal resorption. The litter size decreased at all levels of dietary restrictions, but the birth weight was reduced only with moderate (D70) and severe (D55) restrictions. The litter size and the pup weight of the D70 and D55 mice following ad libitum refeeding were greater than those of their counterparts maintained on restricted feeding.