The tryptophan requirements of young laying pullets

Two experiments were conducted with laying pullets between 32 and 47 weeks of age. In each trial 1728 White Leghorn and 1728 cross-bred pullets were used. A series of diets of increasing protein content was offered. Protein quality was identical in all diets and tryptophan was demonstrated to be the most limiting amino acid in the protein mixture used. The daily tryptophan requirement of the individual pullet was estimated, by indirect methods, to be 2.25 mg/g egg output plus 10.25 mg/kg body weight. Response curves for flocks of pullets are illustrated. Calculated optimum intakes of tryptophan for various ratios of costs of input to value of output are tabulated. It is estimated that for a flock of mean body weight 1.5 kg, producing 55 g egg mass/hen d and consuming 110 g food/hen d, the optimum dietary tryptophan concentration is 1.7 g/kg when the marginal cost of supplying 1 kg tryptophan is 20 times the marginal value of 1 kg egg output.