Effects of dietary supplementation of inorganic, organic or nano zinc forms on performance, eggshell quality, and bone characteristics in laying hens

This study was conducted to evaluate the efficiency of dietary zinc forms and dosages on egg production performance, egg quality, and bone characteristics in laying hens. Forty-two-week-old, 144 Lohmann LSL-Lite laying hens were allocated to 12 experimental groups in a 4 (forms) × 3 (dosages) factorial arrangement. Four zinc forms including zinc-sulphate and zinc-oxide as inorganic forms, zinc-glycine as organic form and nano zinc-oxide powder as nano form at different dosages (50, 75 and 100 mg per kg diet) were tested. Compared to the inorganic (zinc-sulphate) form, the zinc-glycine supplementation significantly depressed the egg weight, egg mass and feed conversion ratio. The eggshell thickness was significantly decreased by supplementation with nano zinc-oxide. The shear force of tibia was significantly decreased by zinc-glycine or nano zinc-oxide supplemented in the diet when compared to inorganic forms of zinc. On the other hand, the dietary 50 mg/kg dosage of zinc was sufficient for optimum performance and the dietary 75 mg/kg dosage of zinc significantly improved shear force of tibia in laying hens. Tibia zinc content increased with the dietary 100 mg/kg dosage of zinc. The interactions between zinc forms and dosages had a significant effect on egg weight, feed intake, feed conversion ratio, eggshell thickness, shear force and shear stress of bone, and tibia calcium concentration. The highest egg weight and the lowest eggshell thickness were observed for the group fed with nano Zn-oxide at 100 mg/kg in the diet. These results showed that nano zinc form supplementation negatively affects the eggshell thickness and bone mechanical properties. The zinc in nano form may not be suggested for feeding laying hens, but other forms of zinc could be used safely in layer diets.