Comparative Contributions of Dietary Protein Quality and Quantity to Growth during Gestation, Lactation and Postweaning in the Rat

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Abstract
The growth promotion by feeding purified diets containing 25%, 12% or 7% of either casein or wheat gluten (W.G.) and the supplementation value of adding cystine to the low casein diets, and lysine or lysine plus threonine to the wheat gluten diets ascertained in rats by comparing the weight achieved at birth, after 3 weeks suckling or 4 weeks post-weaning. Birth weight was depressed by 30% with 7% casein; by 20% with 7% W.G.; by 15% with 25% W.G. compared to controls and there was no change when lysine alone was added to 7% W.G. Addition of lysine plus threonine to 7% W.G., lysine to 25% W.G. and cystine to 7% casein increased birth weight. The weight gain of dams reflected birth weight of pups in most cases. Weaning weight was depressed by 60% with either 12% casein or 12% W.G., and by 40% with 25% W.G. compared to controls. Addition of cystine to 12% casein and lysine to 25% W.G. increased the weaning weight slightly. Addition of lysine, lysine plus threonine or lysine plus glutamic acid (G.A.) to 12% W.G. had no effect on weaning weight. Maternal weight loss was decreased by amino acid supplementation of the diet. Four-week postweaning body weight was equal to the control when cystine was added to 12% casein and lysine was added to 25% W.G. Addition of lysine to 12% W.G. improved the growth rate, and addition of lysine plus threonine further improved the growth rate. Food intake was not decreased by protein deficiency during gestation. Food intake was significantly lowered by protein deficiency during both lactation and post-weaning, however, supplementation of amino acid partially restored food intake to normal levels.