Quantitative nutritional studies with water-soluble, chemically defined diets. I. Growth, reproduction and lactation in rats

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Mixtures of purified l-amino acids, salts, vitamins (B and C), and d-glucose were prepared in 50% aqueous solution and offered, together with a separate supplement of fat-soluble vitamins in corn oil to weanling rats. The tyrosine and cystine components were present in the form of ethyl l-tyrosinate. HCl and ethyl l-cysteinate. HCl, respectively. Calcium and phosphorus were present in the form of the soluble calcium fructose 1,6-diphosphate, and iron appeared in the form of the complex salt, ferrous ammonium sulfate. Potassium and magnesium appeared as the respective gluconates. With these precautions to maintain solubility, the diet solutions were stable and water-clear almost indefinitely. Tests for the presence of microorganisms in diet solutions not sterilized but in which the amino acid and calcium fructose diphosphate components had been carefully crystallized prior to solution revealed complete sterility 0n standing at 37 ° for at least 4 weeks. No bulk was provided in these soluble diets, nor was a training period necessary for their ready imbibition. The intestinal contents were considerably reduced as compared with similar animals on a chow diet, and fecal excretion was scanty and infrequent. The teeth of these animals and the entire length of the gastrointestinal tract were free of any pathologic lesion, gross or microscopic. The diets contained roughly 20% amino acids and 80% glucose, equivalent per gram to 4 cal., or per milliter to 2 cal. The animals grew well at a rate of over 4 g. per day on a diet the “non-essential” amino acid ratios of which were modeled after that of casein. Lesser growth was obtained with diets modeled after other animal proteins, with diets containing fewer “non-essential” amino acids, and with diets modeled after casein but containing dl-amino acids, all however with the same or greater total nitrogen. At maturity the animals on a diet limited in “non-essential” amino acids were mated and produced satisfactory litters which were nursed to weaning. The young, which were smaller than normal, were divided into two groups, one fed on the same diet and the other on that with a full complement of “non-essential” amino acids. Animals on the latter diet recovered rapidly from their bad start and grew at a faster rate than did their litter mates. On mating within each group at the same time, the animals on the superior diet yielded satisfactory litters which were nursed to weaning while those on the inferior diet now showed no pregnancies at all.