Optimal dietary zinc levels of broiler chicks fed a corn-soybean meal diet from 22 to 42 days of age

An experiment was conducted to investigate the effect of dietary zinc (Zn) level on growth performance, Zn concentration, Zn metalloenzyme activity, Zn transporter 2 (ZnT2) mRNA abundance, metallothionein (MT) mRNA abundance and MT concentration in either serum or tissues, so as to evaluate the optimal dietary Zn level of broiler chicks fed a corn-soybean meal diet from 22 to 42 days of age. At 22 days of age, 288 birds were assigned randomly by bodyweight to one of eight dietary treatments of six replicate cages each with six birds per cage, and fed a Zn-unsupplemented basal corn-soybean meal diet containing 27.66 mg of Zn/kg or the basal diet supplemented with 20, 40, 60, 80, 100, 120 or 140 mg of Zn/kg from reagent-grade ZnSO4 center dot 7H(2)O. Regression analysis was performed to estimate the optimal dietary Zn level in the presence of asymptotic response. The results showed that dietary Zn level had no effect (P > 0.25) on the growth performance, serum alkaline phosphatase and 50-nucleotidase activities, and liver copper-Zn superoxide dismutase activity, but affected (P < 0.07) tibia Zn concentration, pancreas Zn concentration, ZnT2 mRNA abundance, MT mRNA abundance and MT concentration. The optimal dietary Zn requirements of broilers from 22 to 42 days of age were 62.44 mg/kg for tibia Zn, 64.30 mg/kg for ZnT2 mRNA abundance and 53.50 mg/kg for MT mRNA abundance based on asymptotic models, respectively. Accordingly, the optimal dietary Zn level for broilers from 22 to 42 days of age was 65 mg/kg in this study.