Therefore, it is not clear why the suppression of Cu/Zn SOD activity in pigs fed the combination Zn diet occurred and was below that found in pigs fed no supplemental Zn in the basal diet (36.09 vs. 58.95 units/mg protein) when all diets contained
approximately 8 mg/kg of Cu, which according to NRC (1998) should be adequate for this age pig.