Efficacy of the D- and L-isomers of N-acetylmethionine for chicks fed diets containing either crystalline amino acids or intact protein.

Chick growth assays were used to evaluate the efficacy and toxicity of the L- and D-isomers of N-acetylmethionine when fed as a source of methionine in crystalline amino acid diets. In agreement with earlier rat studies employing intact protein diets, N-acetyl-L-methionine had a methionine-sparing value of 100% and N-acetyl-D-methionine a value of zero. The former was also observed to be fully effective as a methionine supplement when added to a methionine-deficient diet containing equal protein contributions from soybean, casein and gelatin. Isosulfurous levels of excess L-methionine or N-acetyl-L-methionine were equally growth depressing, but L-methionine elevated spleen iron deposition to a greater extent than N-acetyl-L-methionine. N-acetyl-D-methionine in excess depressed growth only slightly, due entirely to a depression in voluntary food intake, and no evidence of splenic hemosiderosis was observed from this addition.