Toxicity of various organic sulfur compounds for chicks fed crystalline amino acid diets containing threonine and glycine at their minimal dietary requirements for maximal growth.

Five growth assays were conducted with young chicks to study relative toxicities of various organic sulfur compounds. Evaluation of the dietary requirements for glycine and threonine indicated that .52% threonine and .51% glycine were the minimum requirements for maximal gain. To provide a margin of safety .55% threonine and .60% glycine were chosen as levels to use in subsequent assays. A level of 1.25% excess DL-methionine resulted in close to a 40% reduction in growth rate and was chosen as the level to use in later assays. Consumption of excess methionine, calcium methionine hydroxy analogue (OH-M(Ca)) or ethionine resulted in reduced rate and efficiency of gain as well as a lowered concentration of hepatic ATP. DL-homocysteine was equally as toxic as an equimolar level of DL-methionine, but D-methionine was less growth depressing than either Lor DL-methionine. Chicks consuming diets with excess methionine exhibited much greater growth depressions than those fed diets with an equimolar concentration of either OH-M (Ca) or cystine. Homocysteine accumulation in plasma and tissues is thought to be one of several possible factors responsible for lesions associated with methionine toxicity. (