The effect of age on the net requirements for nitrogen,lysine and tryptophan by the well-fed rat

• 1.1. The effect of age on the nitrogen, lysine, and tryptophan content of rats of varying ages fed an adequate diet was studied. On a percentage basis the nitrogen, lysine, and tryptophan levels were found to be essentially the same at all ages, with average figures of 3.24% for nitrogen, 1.47% for lysine, and 0.17% for tryptophan.
• 2.2. Equations of the type W = A − be^−kt were fitted to the data, and growth differential equations were used to estimate daily rate of gain of body weight, nitrogen, lysine, and tryptophan.

The net nitrogen, lysine, and tryptophan requirements were estimated at selected ages by the factorial method. The lysine requirement, expressed as per cent of the protein requirement, was found to diminish progressively with age, being 5.98% lysine for a rat weighing 60 g., and 0.77% lysine for a rat weighing 445 g. Similarly expressed, the tryptophan requirements were found to be 0.8 and 0.3%.