Amino acid interactions in chick nutrition

Synopsis The nature of interactions between leucine, isoleucine and valine has been examined in the young chick. In a preliminary experiment excess leucine was added to a diet limiting in isoleucine. The consequent growth depression was partially reversed by additional isoleucine. The plasma amino acid data indicated that the circulating levels of isoleucine and valine were lowered by the surplus load of leucine. Addition of excess leucine to another diet prevented the growth response to the first limiting amino acid, methionine, but permitted the response if this diet were adequately supplemented with isoleucine. Another diet was prepared in which the level of isoleucine was limiting and the level of valine marginally adequate. The growth retardations following addition of large quantities of leucine were reversed primarily by valine. Complete restoration of growth occurred when both valine and isoleucine were present as additional supplements. Excess methionine added to a diet limiting in valine inhibited growth severely but reversal did not occur following valine supplementation. The results establish the existence of specific interactions between leucine‐isoleucine and leucine‐valine which account adequately for the adverse effects of leucine. Of these interactions, that between leucine and valine appears to be nutritionally more significant. The results are discussed in the light of the concept of agent and target.