The Lysine and Sulfur Amino Acid Requirements at Two Stages of Growth in Chicks

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Abstract
Two sets of two experiments with growing white Leghorn chicks were carried out to compare the methionine and lysine requirements during two phases of growth (1 to 3 and 5 to 7 weeks of age). The methionine requirement was studied with diets containing isolated soy protein, fed at a level that had been found adequate in preliminary experiments to support maximum weight gain. In the lysine requirement studies, sesame meal was used at a protein level determined on the same basis as for the methionine requirement studies. Based on the daily body weight gains, methionine requirements at the two growth periods were 2.4 and 3.0% of protein, respectively. These values are equivalent to 0.61% of the diet for both phases of growth. When body water gain was used as an indirect measure of protein gain, the requirement values were slightly higher. It was therefore concluded that the methionine requirement was either the same, or greater, during the later growth period. Lysine requirements were 5.0 and 4.1% of protein, which are equivalent to 0.94 and 0.70% of the diet, respectively, at the two growth periods. There was no difference in the requirement values obtained whether weight gain or water gain was used as the criterion. This constitutes a tendency different from that observed for the methionine requirement: the lysine requirement was smaller at the later phase of growth regardless of the manner in which it was expressed.