Catch-up growth in rats undernourished for different periods during the suckling period.

Catch-up in body weight, nose-rump length and tail length has been examined in male rats. At birth, pups from several females were pooled and reallocated to provide litters of 16 pups. In group 1, the number was reduced to 8 at day 8, in group 2 on day 15, group 3 were raised in large litters until weaning. Animals reared in litters of 8 were termed controls. All animals were weaned at 22 days, placed two to a cage and provided with food and water ad libitum. They were examined at intervals to day 120. Animals rehabilitated at 8 days had caught up in body weight and 97% of the length of controls on day 120. Rats rehabilitated on day 22 were 88% of the body weight and 97% of the body length of the controls at 120 days. None of the experimental groups achieved the same tail length as the controls. It was concluded that the data do not support the "time tally" mechanism of catch-up growth. This may be due to early timing of the experiment or an oversimplification of the mechanism. It was also concluded that catch-up following neonatal undernutrition in rats is greatly influenced by the normal growth pattern.