Eight-day-old male chicks were used in growth assays to determine the existence of and conditions for a response to dietary inorganic sulfate. Purified crystalline amino acid diets were used in the first five assays and practical corn-soybean meal diets in the final assay. A sulfate-free salt mixture was developed for use in the assays.In the first study, a growth response was obtained to supplemental sulfate when sulfur amino acids (SAA) were deficient (0.40% of the diet) and cystine was first limiting, but no response was obtained when methionine was first limiting, or when sulfur amino acids were adequate (0.60%). In the second assay an approximately equal response was obtained in all cases where cystine was more limiting than methionine, regardless of the breadth of the ratio. In addition, potassium sulfate and sodium sulfate were shown to be equally efficacious as sources of inorganic sulfate for the chick. It was demonstrated in Assays 3 and 4 that no more than 0.1% potassium sulfate was needed to elicit a maximal response in chicks fed 0.25% methionine and 0.15% cystine. Data from both Assays 1 and 5 pointed to the conclusion that there is no dietary requirement for sulfate per se. A response to sulfate supplementation could not be demonstrated when feeding practical corn-soybean meal diets even though chicks responded to supplemental methionine. According to diet analyses, cystine should have been more limiting than methionine, which perhaps suggests that the level of sulfate in the basal diet was too high to allow a response to supplemental sulfate.

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Based upon several recent studies involving reassessment of the essential amino acid requirements of the young chick, levels of dietary arginine, lysine, leucine, valine and glycine were decreased and proline and glutamic acid increased from those present in the Illinois Reference Standard (RS) amino acid mixture. Performance of chicks fed this modified amino acid mixture was as good as or better than that observed with the RS mixture and approached the performance level of chicks fed a practical-type 24% protein corn-soybean meal diet.

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