The Utilization of L-Methionine, DL-Methionine and Methionine Hydroxy Analogue by the Growing Chick1

M ETHIONINE hydroxy analogue, because of its lower cost, is being used as a substitute for supplemental DL-methionine in commercial poultry rations. Nevertheless, its potency as a source of me-thionine activity for the chick remains a controversial question. Some workers (Gor-don and Sizer, 1955; Machlin and Gor-don, 1959; Bruggemann et al., 1962) have found it to be equivalent to DL-methionine, whereas others (Sullivan and Bird, 1957; Calet and Melot, 1961) report that it is less potent. All of these workers used diets containing intact protein ranging from 12% to optimal levels in the diet. There also appears to be a lack of agree-ment on the relative potencies of the L-, D-and DL-isomers of methionine. It has been reported that the D-isomer is as well uti-lized as the L- form when tested with purified diets in which the other amino acids are all in the L- form (Marrett et al., 1964) but not when the diet contains other amino acids in the D- form (Marrett and Sunde, 1965). However, Bruggemann et al. (1962) found D-methionine to be less po-tent than L-methionine added to a diet in which the other amino acids were supplied by protein, the amino acids being in the L-form. It would thus appear that other compo-nents of the diet may influence the relative utilization of the different isomers and ana-logues of methionine. In the following ex-periments, comparisons were made of the