Changes in the digestible lysine and sulfur amino acid needs of broiler chicks during the first three weeks posthatching.

Four experiments were conducted to study the changes in the digestible lysine (DLYS) and sulfur amino acid (DSAA) requirements of broilers during the first 21 d posthatching. Cobb 500 by-product male broilers were fed corn-corn gluten meal-soybean meal diets formulated to be isocaloric and isonitrogenous. Five graded levels of either Lys or SAA were used, varying from 0.78 to 1.28% DLYS (experiments 1 and 2) and from 0.61 to 1.08% DSAA (experiments 3 and 4). Body weight gain (BWG) and gain:feed ratio (GF) were calculated at 4, 7, and 21 d. The DLYS requirements based on BWG varied from 0.98 at 4 d of age to 1.01% at 21 d in experiment 1 and from 0.95 at 4 d of age to 0.99% at 21 d, in experiment 2. Based on GF, the DLYS requirement varied from 1.08 to 1.10% in experiment 1, and from 0.98 to 0.94% in experiment 2 at 4 and 21 d, respectively. The estimated DSAA requirements for BWG varied from 0.83 to 0.88% or from 0.71 to 0.75% for 4 and 21 d in experiments 3 and 4, respectively. For GF, the DSAA decreased slightly from 0.88% at 4 d to 0.83% at 21 d in experiment 3, but did not change in experiment 4 (0.81%). Minimal changes in the DLYS or DSAA estimated requirements occurred during the first 21 d of age, which suggests that the recommended DLYS and DSAA levels determined at 21 d of age appear to be adequate to meet chick needs for the first week of age.