Amino acid utilization as influenced by antibacterial and anticoccidial drugs.

Utilization of amino acids, sulfur-containing amino acid (SAA) in particular, is little affected by antibiotic and anticoccidial compounds. Coccidiosis (i.e., Eimeria acervulina infection) likewise seems to have little effect on SAA utilization. Copper sulfate, a commonly used antibacterial-antifungal compound (used at levels of 100-250 mg/kg diet), interacts with SAA. Hence, at upper levels of copper ingestion (i.e., 250 mg/kg and higher), copper binds SH compounds such as cysteine and reduced glutathione. Dietary SAA requirements are increased in both chicks and rats by dietary copper levels of 250 or 500 mg/kg. Hepatic copper deposition is enhanced by copper feeding and also by E. acervulina infection. These two effects, moreover, appear to be additive. The organic arsenic compound, roxarsone, interacts with SAA also, but in a different way. Thus, whereas added dietary cysteine partially ameliorates copper toxicity due to the binding of copper by cysteine-SH with subsequent excretion, roxarsone toxicity (i.e., 500 mg/kg diet) is exacerbated by supplemental cysteine.