The Threonine Requirement of the Chick

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Abstract
Highly purified diets in which mixtures of amino acids replaced proteins were used to determine the level of threonine required for growth by young White Leghorn chicks. Four experiments were performed in which various levels of DL-threonine were fed; in one experiment, L-threonine was compared to DL-threonine for growth-promoting activity. DL-Threonine was found to be only half as active as L-threonine; hence the requirement is best expressed in terms of the L-form. Under these conditions, the L-threonine requirement was found to be approximately 0.45% of the diet. In two of the experiments poor growth was obtained even at satisfactory levels of threonine. Although the cause for these poor results could not be ascertained unequivocally from the data, it is suggested that the use of small chicks in some experiments was an important factor. A comparison of the threonine requirement with the threonine content of feedstuff proteins indicates that a deficiency of this amino acid under practical conditions is unlikely.