Amelioration of selenium toxicity by arsenicals and cysteine

Young chicks exhibited a 61% reduction in weight gain when a corn-soybean meal diet was supplemented with 15 mg/kg Se provided as Na selenite. The same level of Se provided as selenomethionine depressed weight gain by 32%. Supplementing the high selenite diet with isoarsenous (14 mg/kg As) additions of As2O5, As2O3, phenylarsonic acid, phenylarsine oxide and roxarsone ameliorated the Se-induced growth depression: As2O5 almost totally restored growth rate; As2O3, phenylarsonic acid and phenylarsine oxide gave intermediate responses; and roxarsone gave only a small ameliorative growth response. Arsanilic acid was without effect in stimulating growth rate of selenite-intoxicated chicks. Dietary addition of .4% L-cysteine produced a growth response in selenite intoxicated chicks that was somewhat greater than that obtained with roxarsone; administering both roxarsone and cysteine corrected growth better than either compound given singly. Both roxarsone and As2O5 also effectively ameliorated the Se-toxicity growth depression caused by selenomethionine (15 mg Se/kg) supplementation, but cysteine showed no efficacy against morbidity caused by this form of Se. Liver Se concentration was elevated 10-fold by selenite and 25-fold by selenomethionine supplementation. The arsenic compounds had varying effects on liver Se, whereas cysteine tended to increase Se concentration. These findings suggest that both inorganic and organic arsenicals as well as cysteine ameliorate selenium toxicity by different mechanisms.