Optimal dietary inclusion of organically complexed zinc for broiler chickens.

1. The aim of the present study was to determine the optimal content of organically complexed zinc (Zn) for broiler chickens. 2. Five different Zn and manganese (Mn) dietary contents from organically complexed supplements including a control diet containing 15 mg Mn and 20 mg Zn/kg diet, were randomly fed to one-day-old Cobb broilers (each treatment had 6 replicates of 4 birds) for 35 d. Body weight and feed intake were recorded weekly. At the end of the experiment, two birds from each cage were killed and their right tibia were collected to measure bone size, strength and mineral contents. 3. Body weight gain and total tibia copper (Cu), iron (Fe), Mn and Zn contents increased linearly with supplemental Zn and Mn intake. The optimal Zn requirements for broilers at 1-14 and 14-35 d of age were 58 and 68 mg/kg diet, respectively. 4. Supplementation of Mn and Zn had no effect on tibia bone width and strength, but increased tibia length. 5. In commercial practice, organically complexed Zn may need to be supplemented during the entire period of production at a higher content than NRC recommendation but it is not necessary to exceed 70 mg/kg diet.