This study was conducted to evaluate the influence of increased supplementation of zinc oxide (ZnO) on performance, quality of egg, blood chemistry, and antioxidant ability in serum of laying chickens (Hisex Brown) reared from 22 to 34 weeks of age. Seventy-two 22-week-old laying hens (Hisex Brown) were haphazardly separated into 3 handling collections of 24 chickens (6 replicates per treatment and four laying hens per replicate). Dietary treatments included basal diet without zinc addition for control group while the 2nd and 3rd groups contained basal diet with 25 or 75 mg ZnO/kg diet. Results showed that the higher level of ZnO (75 mg ZnO/kg diet) elevated (P < 0.01) feed intake during all studied periods compared with the control group and other groups that contained ZnO. The handling groups supplied with 75 mg ZnO/kg diet gave the worst feed: egg ratio within the whole period and the intervals compared with the control and other ZnO levels. Supplementation of zinc decreased egg number and egg output when compared with the control groups. Egg quality traits were statistically differed due to dietary ZnO supplementation except egg shape index, yolk %, and albumin %. Supplementation of zinc decreased triglyceride (P = 0.001) of laying hens. The low-density lipoproteins (LDL) cholesterol level in serum was decreased with 75 mg ZnO/kg in comparison with all treatment groups. Zinc supplementation increased the level of serum zinc without differences in supplemented zinc levels. Dietary supplemental zinc did not affect antioxidant parameters in the serum. It is concluded that dietary zinc supplementation up to 75 mg/kg used as effective supplement to enhance zinc status and antioxidant ability and activities in laying hens.
Keywords: Blood chemistry; Egg quality; Layers; Performance; Zinc oxide.