Perinatal mortality, growth and survival to weaning in offspring of rats reared on diets moderately deficient in protein.

I. The reproductive performance of rats reared from weaning on a moderately proteindeficient (LP) diet containing Sogcaseinjkg, or on a control diet (HP) containing 250 g casein/kg has been studied. Although the rate of growth was reduced in LP animals, these rats eventually achieved the same adult weight and appearance as the controls. 2. Weight gain during the first z weeks of gestation was similar in the two dietary groups, but during the 3rd week H P rats gained twice as much weight as the LP animals. 3. Viable litters were produced by 78 % of the HP rats mated but by only 33 % of LP rats. Most of the offspring which died did so during or soon after birth; so the perinatal mortality for the offspring of LP rats was 73 % compared with only 26 76 for control rats. After the first few days of life, the chance of survival of HP and LP offspring was similar. 4. At birth the mean body-weight of the offspring was 5.4 g for H P offspring and 4.7 g for LP offspring. However, the mean body-weight at birth of viable offspring was similar whether they were from HP or LP rats (HP 5-6 g; LP 5.3 g). At weaning, HP offspring weighed 31.2 g and LP offspring only 13.3 g. 5 . When the HP diet was given to LP rats at parturition, the viablc offspring achieved a weaning weight of 3 I' j g, but there was no decrease in the perinatal mortality.