Growth and Development With Special Reference to Domestic Animals XXXVI: Endogenous Nitrogen and Basal Energy Relationships During Growth
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The ratio of endogenous urinary nitrogen to basal metabolism is about 1 mg per C~l. for weanling rats and about 1.5 mg per Cal. for mature rats. The correlation between endogenous nitrogen and body weight is better than between endogenous nitrogen and basal metabolism. Two methods (Time-curve and Composite or Smuts) were used for measuring the minimum endogenous nitrogen excretion of growing rats. These methods gave comparable results when the minimum urinary nitrogen excretion was related to the initial body weight or basal heat production. Variations in the endogenous nitrogen excretion may account for the discrepancies in biological values of proteins as reported in the literature. Using Smuts' method, in which urine is collected between the 7th and 13th days on a N-poor diet, rats weighing over 100 gms taken from a high (30 per cent) protein diet excreted about 26 per cent more nitrogen per unit body weight than their paired litter mates taken from a low (13 per cent) protein diet. The basal metabolism per unit body weight of the high protein rats was 7.6 per cent lower than that of the low protein rats.