Sulfur Utilization by the Chick with Emphasis on the Effect of Inorganic Sulfate on the Cystine-Methionine Interrelationship

Abstract

Young chicks were employed to determine the effect of dietary inorganic sulfate on performance and body composition and on the capacity of cystine to spare methionine for chick growth. Cystine was included in the purified diets to provide 0, 20, 40, 50, 60 or 70% of the total sulfur-bearing amino acids (SAA), the balance coming from methionine. Two dietary levels of K₂SO₄ were evaluated, 0 and 0.10%. When SAA were at or near adequacy, the optimal percentage from cystine was 48.4% in the presence of dietary K₂SO₄ and 52.7% in its absence. When SAA were set at a deficient level, optimal performance occurred when cystine furnished 41.3% and 48.2% of the SAA need, respectively, in the presence and absence of K₂SO₄. Body composition data confirmed that the response to inorganic sulfate was not due to water retention but instead to increased retention of protein and calories. An assay was conducted to compare 0.10% K₂SO₄ with isosulfurous quantities of taurine and cysteine when added to a sulfate-free diet first limiting in cysteine. Chicks receiving either K₂SO₄ or cysteine exhibited greater gains than those receiving the basal diet, but no response was observed from taurine addition. Gain responses to sulfur sources could be explained entirely on the basis of food intake.