Catch-up growth in male rats after growth retardation during the suckling period

Abstract

On the day of birth 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 two to a cage with unlimited food and water. The pups were weighed and measured on days 3, 7, 14, 28, 35, 49, 63, 77, 91, 105, 119, and 228, whole body radiographs were also taken which enabled an assessment of skeletal maturity to be made. The experiment was continued until skeletal maturity reached 98% of the adult value in both groups. At 21 days the undernourished males were only 60% (P < 0.001) of the weight of the normal males. After weaning, and hence during rehabilitation, the difference between the groups progressively diminished, the undernourished being 65% of the normals at 28 days (P < 0.001), 72% at 35 days (P < 0.001), 83% (P < 0.001) at 49 days, and 90% (P < 0.05) at 119 days. The ultimate difference, however, at 228 days, when bone maturity was 98% of the adult value, remained significant with undernourished 88% (P < 0.001) of the normals; the catch-up was not complete. Both groups had a marked increase of velocity after weaning, rising to a peak around 55 days. During this period the undernourished still grew at an absolutely slower rate than the well nourished normals; therefore, in relation to age they did not show a catch-up in weight during this time. In relation to their body weight, however, they were growing faster than the normals; their 28–49-day rate being 19% of their weight at 28 days, compared with that of the normals, 14%.At weaning, the undernourished were only 87% (P < 0.001) of the nose-rump length of the normals, and at 28 days, despite 7 days of rehabilitation, they had further decreased to 85% (P < 0.001). Thereafter, their velocity equaled or exceeded that of the normals, so that by 35 days they were 90% (P < 0.001) as long, by 63 days 97%, and by 120 days 98% as long, with a difference that was no longer statistically significant. The velocity curves showed that a catch-up velocity occurred, but not immediately after rehabilitation commenced. The tail length was less affected than the body length until the last part of the suckling period. However, by the time of weaning, the mean for the undernourished animals was 87% (P < 0.001) of the normals. The velocity of the undernourished animals failed to increase immediately after weaning and at 28 days the mean for the undernourished animals had fallen to 80% (P < 0.001) of the normals. Thereafter, the same sort of catch up occurred as for body length, although the extent was less and by the end of the growth period the undernourished animals still had significantly shorter (P < 0.05) tails than the normal animals, finally averaging 97%. By 14 days the skeletal maturity scores of the undernourished had fallen behind thenormals by an amount corresponding to about a day’s growth. After weaning the undernourished group fell still further behind, at 28 days being some 5 (P < 0.001) days retarded. Only after 35 days did the undernourished animals begin to overtake the normals as the latter’s increments in score diminished. At weaning the normals were longer even for their maturity score. Thus the difference in size was not solely due to slowing down development in the undernourished, for if this were so the two groups would be equal in size at equal maturity scores. The two groups did become equal in weight and lengths for maturity at a score which corresponded to about 28 days in normals and 35 days in the undernourished. From 35 days to about 75 days the undernourished suffered primarily from a delay in growth, so they were in correct size- maturity proportion but delayed on their time path. However, later the normals increased their weight for given bone maturity relative to the undernourished and at the very end of the growth period did so markedly. Thus the final weight deficit of the undernourished was not due to deficit in the skeleton but in some other tissue. At the end of growth the undernourished were only 88% of the weight of the normals, this difference being significant (P < 0.001.) In nose-rump length they had caught up to 98% of the normals, the 2% difference not being statistically significant. In tail length they reached 97% of the normals (P < 0.05). © 1974 International Pediatric Research Foundation, Inc.