Effects of nanosized zinc oxide and γ-polyglutamic acid on eggshell quality and serum parameters of aged laying hens

In order to increase zinc (Zn) absorption and improve eggshell quality, diets for aged laying hens were supplemented with different Zn sources and the effects on egg production, eggshell quality and serum parameters were recorded. Seventy-five 64-week old brown layers were individually caged and randomly allotted to five treatment groups: an un-supplemented Control and four groups, where the following Zn sources were added to the diets, ZnO (group ZnO), Zn-methionine (group Zn-Met), nanosized ZnO (group nanoZnO) and γ-PGA-nano ZnO (group γ-PGA-nanoZnO). The Zn level was maintained at 80 mg/kg in the supplemented diet, while the Control group received Zn at 40 mg/kg diet. The results indicated that the average daily feed intake was highest in group nanoZnO (p < 0.05), whereas further performance parameters were not influenced by treatments. Eggshell thickness was increased in group γ-PGA-nanoZnO (p < 0.05). Zn content in eggshells and Zn concentration in serum were increased in groups Zn-Met, nanoZnO and γ-PGA-nanoZnO (p < 0.05). Serum ghrelin concentration was significantly elevated in all Zn-supplemented groups, but further increased in groups nanoZnO and γ-PGA-nanoZnO (p < 0.05). Carbonic anhydrase activity was highest in group γ-PGA-nanoZnO and lowest in group Zn-Met (p < 0.05). Compared to the Control and group ZnO, supplementation of γ-PGA-nanoZnO and nanoZnO increased serum IgG levels (p < 0.001). In conclusion, dietary supplementation of nanoZnO and γ-PGA-nanoZnO increased Zn content in eggshells, serum Zn concentration, ghrelin and IgG levels of aged layers when compared to regular ZnO. Compared to Zn-Met, the serum carbonic anhydrase activity and ghrelin levels were also increased. Thus, nanosized ZnO alone or mixed with γ-PGA has positive effects on the Zn status of aged layers.