Experiments on the Requirement of Inorganic Sulfate by the Chick

In order to ascertain the essentiality of inorganic sulfate to the chick, a series of three experiments was conducted. A basic crystalline amino acid diet containing no intact protein supplemented with vitamins and sulfate free minerals was employed as the basal diet in all experiments. Increasing the dietary level of total sulfur amino acids (TSAA) as provided by methionine alone or methionine plus cystine from 0.30, 0.33 or 0.45 to 0.6, 0.67, 0.90 or 1.00% resulted in significant improvement in weight gains and feed conversions. Inorganic sulfate (as K2SO4), significantly stimulated growth at suboptimal TSAA levels but not when TSAA were 0.9% or more. In Experiment 2, optimal growth response was obtained when inorganic sulfate supplied 13.5% of the dietary sulfur with the remainder contributed in the form of dl-methionine. Although increasing the TSAA level to 1.00% further stimulated growth somewhat, inorganic sulfate supplementation at this level had a detrimental effect on growth and feed conversion. The addition of 0.24% potassium sulfate to diets containing 0.45% TSAA supplied as 50/50 or 65/35 methionine to cystine significantly improved weight gains. At 0.90% TSAA, nonsignificant although consistent growth responses were obtained by the supplementation of 0.12% potassium sulfate in diets with either ratio of methionine to cystine. Inorganic sulfate supplementation appeared most effective when the methionine cystine ratio was 65/35. Optimal growth, however, was obtained when the TSAA were supplied in a 50/50 ratio of methionine to cystine. In this case, the total dietary sulfur contribution by methionine, cystine and potassium sulfate was 41, 50 and 9% respectively.