Effects of age on the tryptophan requirement of laying hens

White Leghorn pullets which had been used for an assay of tryptophan requirement between 32 and 40 weeks of age were used for similar determinations between 63 and 73 and, after a moult, from 97 to 106 weeks of age. A tryptophan-limiting protein mixture was used and by dilution seven dietary protein contents were produced, supplying from 0.84 to 1.92 g tryptophan/kg diet. The diet of lowest protein content was also supplemented with free tryptophan. These diets were fed in experiments using 24 groups of 72 pullets at 63 to 73 weeks and 45 groups of 21 hens at 97 to 106 weeks. The relationship between egg output and tryptophan intake was the same in moulted hens as in young pullets, but pullets of 63 to 73 weeks of age yielded a different response curve; more tryptophan being needed for a given egg output. It is concluded that tryptophan required, per day, does not decrease during the first laying year, despite a decrease in rate of egg output.