The Utilization by the Chick of Protein-Bound as Compared to Free Dietary Lysine

FISHER and Johnson (1956) reported a higher lysine requirement for maintaining egg production with free amino acid diets than is recommended with practical rations, although more recent work (Johnson and Fisher, 1958) has since shown that when a better balance of amino acids is attained, the requirement is no longer elevated. For the determination of a lysine requirement for growth, basal diets are commonly employed in which the proteins supply greatly different portions of this amino acid toward the requirement with consequently highly variable contributions of free lysine. Although an equally efficient utilization of the two lysine forms is generally assumed, experimental evidence is lacking. Supplementation with the two lysine forms (free and protein-bound) results in two types of diet which are not strictly comparable. They differ in protein content, in amino acid pattern, and their efficiency might be specifically affected by unknown components contained in the protein source. An …