Influence of Addition of Water or “Nonessential” Nitrogen on Growth of Rats Fed Low Levels of Essential L-Amino Acids

Summary Male weanling rats were fed casein or purified amino acid (AA) diets equivalent to 10% protein (N X 6.25) to determine the effect of the addition of 50% water, nonessential amino acids (NEAA) or other N sources on growth. The daily weight gain of rats fed the wet casein diet (6.0 g) or the wet AA diet of Ranhotra and Johnson (5) (5.8 g) was significantly greater than that of rats fed comparable dry diets (5.3 and 4.5 g, respectively). However, the addition of water to a variety of other diets containing different AA mixtures but the same non-nitrogenous ingredients did not significantly improve growth. The carcass fat was significantly higher with the wet AA diets than with the dry AA diets. The data indicate that the response to added water is related to the balance of the AA in the diet. Rats fed the dry casein or AA diet at the 15% protein equivalent level had a significantly faster rate of gain and improved food efficiency over those fed the diets reduced to 10% protein equivalent, even though the essential AA were supplied in adequate amounts. The addition of a combination of glycine and glutamic acid, urea, or a mixture of NEAA significantly improved growth, but diammonium citrate or other NEAA added singly did not give a significant response.