Zinc requirement of yellow broilers from forty-three to sixty-three days of age.

【Objective】An experiment was conducted to investigate dietary zinc level on growth performance,antioxidant capacity,immune function and zinc depositionin in Lingnan yellow broilers from 43 to 63 days of age,and to estimate the optimal dietary zinc level for yellow broilers.【Method】A total of 1080 43-day-old male broilers were randomly assigned to six dietary treatments with six replicates and thirty birds with each pen.The groups received the same basal diet supplemented with 0(control group) ,20,40,60,80 and 120 mg·kg -1 zinc from zinc sulfate(ZnSO4 . H2O) ,respectively.The trial lasted for 21 days.【Result】 Dietary zinc supplementation had no effect on the growth of broilers(P0.05) .Zinc supplementation increased the activities of GSH-Px,CuZnSOD and AKP in serum(P0.05) ,and significantly raised GSH content in serum,zinc concentrations in serum and tibia,MT content in serum and liver(P0.05) ,and addition with 60 mg·kg -1 zinc showed the best result for AKP activity in serum and zinc concentrations in tibia.Supplementation with 20 to 40 mg·kg -1 zinc significantly elevated thymus index,and addition of 20 to 80 mg·kg-1zinc significantly improved the index of Bursa of Fabricius of broilers at 63d(P0.05) .Zinc addition had no effect on spleen index,CuZnSOD activity in liver and tibia ash percentage(P0.05) .【Conclusion】Only take consideration of growth performance of broilers,there's no need to supplement maize-soybean meal diet with zinc.Based on the criteria including AKP activity in serum and zinc concentration in tibia,the optimal supplemental zinc level estimated by variance analysis and multiple comparisons for broiler chicks was 78 mg·kg-1for 43-63-day-old broilers,but the optimal supplemental zinc levels estimated byNLIN were 81 and 60 mg·kg -1,respectively.