AbstractThis study was designed to measure the responses of Dekalb laying hens to three amino acids such that the optimum economic amino acid intakes of these hens could be determined, taking into account variation in body weight and potential egg output in the population as well as changes in egg revenue and feed price. Three experiments were conducted with Dekalb White laying hens during the period from 33 to 48 weeks of age, with each trial being divided into four periods of 28 days. Responses were measured to intakes of lysine, methionine + cysteine and threonine. The laying hens were distributed in a completely randomized design among eight treatments and six replicates. The treatments consisted of increasing levels of each of the amino acids under test to obtain a response curve. These levels were obtained using a dilution technique, and a control treatment was included to confirm that responses were due to the test amino acid. Egg production (%), feed intake (g), body weight (kg), egg output (g/day) and egg weight (g) were measured. The control treatment confirmed that the amino acid under test was limiting in each assay. The Reading model was fitted to the data in each trial using the relevant amino acid intakes and egg outputs. The coefficients of response obtained were 8.58 mg/g, 7.96 mg/g and 6.73 mg/g egg output, and 36.6 mg/kg, 50.8 mg/kg and 37.2 mg/kg body weight for lysine, methionine + cysteine and threonine, respectively. Assuming a maximum egg output of 55±12.5 g/day, an average body weight of 1.45±0.2 kg and a cost ratio of the amino acid (c/mg) and egg (c/g) of 0.0023 (lysine), 0.0025 (methionine + cysteine) and 0.0034 (threonine), the optimum economic intakes of each amino acid under current Brazilian conditions were 746, 717 and 593 mg/bird/day for the three amino acids, respectively.