Influence of choline and sulfate on copper and toxicity and substitution of and antagonism between methionine and copper supplements to chick diets.

Studies were conducted to determine if the deleterious affects on chick growth of the primary antagonism between methionine and copper involves the homocysteine moiety or labile methyl group of methionine. A .1% choline supplement resulted in performance response similar to that of a .2% L-methionine supplement in the absence but not in the presence of 500 mg/kg copper from cupric sulfate. Similar results were observed when the levels of methionine and choline were doubled. Sulfate, with or without choline, had little effect in the presence of cupric sulfate. When cupric acetate was used instead of cupric sulfate, a small but nearly significant (P = .08) response to potassium sulfate was observed. Maximum performance with .29% supplemental methionine and 188 mg/kg Cu was predicted from a response surface analysis. The methionine requirement was increased by feeding copper. However, the increase in methionine requirement was accompanied by an improvement in growth rate and feed efficiency. This may explain why levels used of methionine and total sulfur-containing amino acids appear to be higher under field conditions (with pharmacological levels of copper) than in laboratory conditions (without pharmacological levels of copper). The primary antagonism between methionine and copper involves the homocysteine moiety, not the labile methyl groups.