Efficacy of D-, L- and DL-methionine for growth of chicks fed crystalline amino acid diets.

Four assays employing young male chicks were conducted to evaluate the relative efficacy of D-, L- and DL-methionine and to estimate the requirement for D- and L-methionine when serving as the sole source of sulfur amino acids or when added to a diet containing 0.27% L-cystine. Crystalline amino acid diets containing 14.9% protein equivalent and 4200 kcal. M.E./kg. were used in all assays. L-methionine supported faster and more efficient gains than D- or L-methionine when fed at levels below thhe requirement. At levels of supplementation near the requirement, however, equal efficacy was attained. When serving as the sole source of sulfur amino acids, the requirement as estimated by least squares for optimal gain was 0.58% of the diet or 104 mg./day for L-methionine and 0.59% or 104 mg./day for D-methionine. In the presence of cystine, the requirements were estimated at 0.27% or 49 mg./day and 0.30% or 52 mg./day for L- and D-methionine respectively. The results indicate that at lower levels of supplementation, L-methionine is a better source of sulfur amino acids than D-methionine. On the other hand, L- and D-methionine appear to have equal efficacy when incorporated into diets that are only marginally deficient in sulfur-bearing amino acids.