RESUMEN
This study was conducted to determine the effect of dietary zinc (Zn) sources and their levels on the performance, egg quality, tissue mineral concentrations and bone mechanical traits of laying hens. Two hundred seventy, 44-week-old, Super Nick white laying hens were randomly distributed to 15 experimental groups in a 3 (sources of Zn) × 5 (levels of Zn) factorial arrangement, using groups of 18 birds with 6 replicates. The 15 experimental diets consisted of three sources of Zn (zinc-oxide as an inorganic form, zinc-proteinate as an organic form and nano zinc-oxide powder as a nano form) and five different levels of Zn (20, 40, 60, 80 and 100 mg Zn/kg diet). The experiment lasted 12 weeks. Dietary Zn sources, Zn levels and their interactions had no significant effect on the performance parameters between the treatment groups, nor a significant effect on eggshell weight and eggshell breaking strength. Eggshell thickness and eggshell Ca and P contents were significantly affected by the different dietary Zn sources. Dietary Zn sources, Zn levels and their interactions had no significant effect on tibia Ca and P contents, and also had no significant effect on tibia Zn content. Liver Zn content was significantly affected by the dietary Zn sources. Serum Zn content was not affected by the dietary treatments. Dietary Zn sources, Zn levels and their interactions had no significant effect on tibia weight, tibia stress and tibia breaking strength, as tibia mechanical parameters. Excreta Zn content decreased linearly when hens were fed nano Zn compared to organic and inorganic Zn, and excreta Zn content also linearly increased with increasing dietary Zn levels. In conclusion, 20 mg/kg of supplemental Zn is optimal for sustaining performance, good eggshell quality and bone status, while also reducing Zn excretion and soil pollution, with organic (Zn-proteinate) and nano (ZnO) Zn as the preferred forms in laying hen diets.