Effect of high-level copper feeding on the sulfur amino acid need of chicks fed corn-soybean meal and purified crystalline amino acid diets.

Supplementation of a corn-soybean meal diet with .05% methionine maximized gain and feed efficiency of three-week-old chicks fed copper at either 0 or 250 mg/kg. With copper present at 500 mg/kg, the supplemental methionine requirement was in excess of .10%. Liver copper stores of chicks fed copper at 250 mg/kg declined linearly as supplemental methionine level increased, but methionine level had no effect on liver copper when chicks were fed 500 mg/kg copper. Liver copper accumulation did not occur in chicks fed 250 mg/kg copper when supplemental sulfur was provided as a combination of .05% methionine and 1800 mg/kg sulfide. Irrespective of methionine level, sulfide addition reduced liver copper by one-half in birds fed 500 mg/kg copper. Chicks fed the purified diet were appreciably more susceptible to copper toxicity than those fed the corn-soybean meal diet. Chicks fed the purified diet without supplemental copper required .52% sulfur amino acids (SAA). Chicks fed copper at 250 and 500 mg/kg required .65 and .70 SAA, respectively, although gain and feed efficiency were still depressed when compared with the performance of the control birds. Higher levels of methionine failed to restore growth rates to those achieved with birds fed no supplemental copper. Supplementing the copper-containing diets with up to 1.6% cystine improved performance some but failed to completely overcome the growth depressing effect of copper at 500 mg/kg. Results of additional studies indicated that the purified diet containing .70% SAA and 500 mg/kg copper was nutritionally adequate and that the marked toxicity of copper when fed in the purified diet was due to the chemical nature of the diet rather than to any specific copper-induced nutritional deficiencies.