Abstract
Extract: On the day of birth, the pups from several dams were pooled and reallocated so that some of the dams had 8 pups while others had 16. The pups were weaned at 21 days and placed 2 to a cage with unlimited food and water. The pups were weighed and measured on days 3, 7, 14, 21, 28, 35, 49, 63, 77, 91, 105, 119, and 228 and whole body radiographs were also taken, which enabled bone lengths to be measured and an assessment of skeletal maturity to be made. The experiment was continued until skeletal maturity reached 95% of the adult value in both groups. Data for females are reported and compared with those for males.
At weaning the undernourished females were only 63% (P < 0.001) of the weight of the normal females. After weaning, and hence during rehabilitation, the percentage difference between the groups progressively diminished; the undernourished were 67% (P < 0.001) of the normal group at 28 days, 72% (P < 0.001) at 35 days, 87% (P < 0.01) at 49 days, 93% at 91 days, and 95% (difference not significant) on completion of the experiment at 228 days. The total weight gain from 21 to 228 days was similar in both groups. The weight difference (15 g) was significant at 21 days when it represented a weight difference of 38% but the same weight difference (14 g) was not significant at 228 days when it represented a difference of only 5%.
In nose-rump length the undernourished were 84% of the normal rats at weaning. At 28 days they were 83% (P < 0.001), their velocity in length having nearly equalled that of the normals. From 28 days until 100 days their velocity exceeded that of the normals, so that by 35 days they were 91% (P < 0.001) of the length of the normals, by 49 days 95% (P < 0.001), by 63 days 99%, and by 90 days 100%. The catch-up was rapid and complete.
At weaning the tail length was 85% (P < 0.001) of the normals and at 28 days 82%. The catch-up in velocity was delayed until the 28–35-day period. The velocity exceeded that of the normal rats from 35 days on, and the undernourished caught up to 89% (P < 0.001) of the normals at 49 days and 95% (P < 0.01) at 90 days. At 228 days, however, catch-up was not quite complete, the undernourished being 96% of the normal, a difference which was just statistically significant (P < 0.05).
At 21 days the undernourished were about 1.5 days behind (P < 0.001) in skeletal maturity and at 35 days still further behind. After this the undernourished steadily caught up. At weaning the undernourished were slightly lower in weight and lengths for bone maturity, which indicated a greater effect on body measurements than on bone maturation. As in the males the two groups became equal for bone maturity at a score which corresponded to about 28 days in normals and 35 days in undernourished. Thereafter there was little consistent difference in nose-rump length, but the tail length and weight in normal rats remained a little greater at given maturity score.
The effects of undernutrition in the females are qualitatively very similar to those in males, even in details of the growth curves. Quantitatively, the females, as expected, showed still greater capacity to catch up than males. At 35 days there is practically no difference in percentages between the sexes and thereafter in lengths and bone maturity the differences are very small. In weight, however, the undernourished males fare less well than the undernourished females. The difference is due to the greater increase of weight of the normal males from 105 days to 228 days. The sex differences clearly result from a lower mature weight for length in females and underline our previous conclusion that the lack of complete catch-up in weight under these experimental conditions results not from a skeletal deficit, but from a deficit in soft tissue.
Speculation: Female rats show a response to undernutrition during the suckling period similar to male rats, and a more nearly complete catch-up or rehabilitation. This study demonstrates that this statement applies to body weight but not to length, and indicates a differential susceptibility of nonskeletal tissues in males and females.
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Williams, J., Tanner, J. & Hughes, P. Catch-up Growth in Female Rats after Growth Retardation during the Suckling Period: Comparison with Males. Pediatr Res 8, 157–162 (1974). https://doi.org/10.1203/00006450-197403000-00002
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DOI: https://doi.org/10.1203/00006450-197403000-00002
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