Abstract
An experiment was conducted to estimate the optimal dietary zinc (Zn) level of brown-egg laying hens fed a corn-soybean meal diet from 20 to 40weeks of age. A total of 120 20-week-old Beijing Red commercial laying hens were randomly allotted by bodyweight to one of five treatments with six replicates of four birds each in a completely randomized design, and fed a Zn-unsupplemented corn-soybean meal basal diet containing 27.95mg Zn/kg by analysis and the basal diets supplemented with 30, 60, 90, or 120mg Zn/kg as Zn sulfate (reagent grade ZnSO4·7H2O) for a duration of 20weeks. Laying performance, egg quality, tissue Zn concentrations, and activities of serum alkaline phosphatase (AKP), and liver copper-Zn superoxide dismutase (CuZnSOD) were measured. Regression analyses were performed to estimate an optimal dietary Zn level whenever a significant quadratic response (P<0.05) was observed. Tibia Zn concentration (P=0.002) and serum AKP activity (P=0.010) showed significant quadratic responses to dietary supplemental Zn levels. The estimates of dietary Zn requirements for brown-egg laying hens from 20 to 40weeks of age were 71.95 and 64.63mg/kg for tibia Zn concentration and serum AKP activity, respectively. The results from this study indicate that the tibia Zn might be a more suitable and reliable parameter for Zn requirement estimation, and the optimal dietary Zn level would be about 72mg/kg for brown-egg laying hens fed a corn-soybean meal diet from 20 to 40weeks of age.
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