Four experiments were conducted todetermine the interactive effects of pharmacologicalamounts of Zn from ZnO and Cu from organic (Cu-AA complex; Cu-AA) or inorganic (CuSO4) sources ongrowth performance of weanling pigs. The Cu was fedfor 4 (Exp. 1) or 6 (Exp. 2, 3, and 4) wk after weaning,and Zn was fed for 4 (Exp. 1) or 2 (Exp. 2, 3, and 4) wkafter weaning. Treatments were replicated with 7 pensof 5 or 6 pigs per pen (19.0 d of age and 5.8 kg of BW, Exp. 1), 12 pens of 21 pigs per pen (about 21 d of age and 5.3 kg of BW, Exp. 2), 5 pens of 4 pigs per pen (20.3 d of age and 7.0 kg of BW, Exp. 3), and 16 pens of 21 pigs per pen (about 21 d of age and 5.7 kg of BW, Exp. 4). In Exp. 1 and 2, Cu-AA (0 vs. 100 mg\/kg of Cu) and ZnO (0 vs. 3,000 mg\/kg of Zn) were used in a 2 \u00d7 2 factorial arrangement. Only Exp. 1 used in-feed antibiotic (165 mg of oxytetracycline and 116 mg of neomycin per kilogram feed), and Exp. 2 was conducted at a commercial farm. In Exp. 3, sources of Cu (none; CuSO4 at 250 mg\/kg of Cu; and Cu-AA at 100 mg\/kg of Cu) and ZnO (0 vs. 3,000 mg\/ kg of Zn) were used in a 3 \u00d7 2 factorial arrangement. In Exp. 4, treatments were no additional Cu, CuSO4 at 315 mg\/kg of Cu, or Cu-AA at 100 mg\/kg of Cu to a diet supplemented with 3,000 mg\/kg of Zn from ZnO and in-feed antibiotic (55 mg of carbadox per kilogram of feed). In Exp. 1 and 2, both Zn and Cu-AA improved ADG and ADFI. No interactions were observed, except in wk 1 of Exp. 2, where Zn increased the G:F only in the absence of Cu-AA (Cu- AA \u00d7 Zn). A naturally occurring colibacillosis diarrhea outbreak occurred during this experiment. The ZnO addition reduced the number of pigs removed and pig-days on antibiotic therapy. In Exp 3, ADFI in wk 2 was improved by Zn and Cu with no interactions. In wk 1, G:F was reduced by ZnO only in the absence of Cu (Cu \u00d7 Zn). Feeding Zn decreased fecal microbiota diversity in the presence of CuSO4 but increased it in the presence of Cu-AA (Cu source \u00d7 Zn). In Exp. 4, Cu supplementation improved the overall ADG and G:F. The CuSO4 effect on G:F was greater than the Cu-AA effect. Our results indicate that pharmacological amounts of ZnO and Cu (Cu-AA or CuSO4) are additive in promoting growth of pigs after weaning.<\/p>\n