LAUSR

The current dietary copper (Cu) requirement (8 mg/kg) of broilers is mainly based on growth, hemoglobin concentration, or hematocrit, which might not be the most sensitive indices to evaluate dietary Cu requirements of broilers. The present study was carried out to estimate dietary Cu requirements of broilers fed a conventional corn-soybean meal diet from 1 to 21 d of age using biochemical or molecular biomarkers. A total of 384 1-d-old Arbor Acres male broilers were randomly allocated to 1 of 6 treatments with 8 replicates and fed a Cu-unsupplemented corn-soybean meal basal diet containing 5.17 mg Cu/kg by analysis and the basal diet supplemented with 3, 6, 9, 12 or 15 mg Cu/kg as CuSO4⋅5H2O for 21 d. Regression analysis was performed to estimate the optimal dietary Cu level using the broken-line model. Dietary supplemental Cu level affected (P < 0.05) Cu contents in serum and liver and kidney monoamine oxidase (MAO) activity, but had no effects (P > 0.05) on the growth performance, Cu contents in heart, kidney, pancreas and spleen, Cu- and zinc-containing superoxide dismutase (CuZnSOD) activity and ceruloplasmin content in serum, CuZnSOD and cytochrome c oxidase (COX) activities and ceruloplasmin, CuZnSOD, MAO A, MAO B, COX4I1 and COX1 mRNA and protein expressions in the above tissues of broilers. As dietary supplemental Cu levels increased, Cu contents in serum and liver increased linearly (P < 0.05), but kidney MAO activity decreased linearly and quadratically (P < 0.05). The estimated dietary Cu requirement based on the fitted broken-line model (P = 0.035) of kidney MAO activity was 11.30 mg/kg. In conclusion, kidney MAO activity is a new and sensitive criterion to evaluate the dietary Cu requirement of broilers, and the dietary Cu requirement was 11.30 mg/kg for broilers fed the conventional corn-soybean meal diet from 1 to 21 d of age, which is higher than the current National Research Council (NRC) Cu requirement (8 mg/kg) of broilers.