Effect of in ovo zinc injection on the embryonic development, tissue zinc contents, antioxidation, and related gene expressions of broiler breeder eggs

Two experiments were conducted to investigate the effect of in ovo zinc (Zn) injection on the embryonic development, tissue Zn contents, antioxidation and related gene expressions of fertilized eggs of Arbor Acres broiler breeders. Experiment 1 was conducted to determine an optimal embryonic age for early in ovo injection. A total of 720 fertilized eggs with similar weights were randomly allotted to 4 treatments with 6 replicates per treatment and 30 eggs per replicate in a completely randomized design. The eggs were injected with 0.1 mL sterilized water at 3, 6 and 9 embryonic days of incubation (E3, E6 and E9) or non-injection (the control), respectively. The results from experiment 1 showed that E3 and E6 injections increased (P<0.05) the embryonic mortalities, and decreased (P<0.05) hatchabilities compared to the non-injected control, but no differences (P>0.05) between E9 injection and the non-injected control were observed in either embryonic mortality or hatchability. The findings suggest that the E9 is the optimal embryonic age for early in ovo injection. In experiment 2, a total of 672 fertilized eggs with similar weights were randomly allocated to 7 treatments with 6 replicates per treatment and 16 eggs per replicate in a completely randomized design. The eggs were injected with 0 (the negative control), 50, 100, 150, 200, or 250 μg Zn/egg as reagent grade ZnSO4·7H2O in a 0.1-mL solution, or non-injection (the positive control), respectively at E9-10. The results from the experiment 2 demonstrated that no differences (P>0.05) among 50 and 100 μg Zn/egg groups and the negative control were observed in the embryonic mortality and hatchability, however, the injection of 200 μg Zn/egg increased (P<0.05) the embryonic mortality, and injections of 150 and 200 μg Zn/egg decreased (P<0.05) hatchabilities compared with the controls. The embryonic tibia Zn contents at E20 were increased (P<0.05) by injections of 150, 200 and 250 μg Zn/egg. Zinc injection did not affect (P > 0.05) malonaldehyde (MDA) contents, copper- and Zn-containing superoxide dismutase (CuZnSOD) activities and mRNA expression levels in the liver and heart of chick embryos at E15 and E20. Compared with the negative control, injections of 50, 150 and 200 μg Zn/egg up-regulated (P<0.05) the metallothionein (MT) mRNA expression levels in the embryonic liver at E20. These results indicated that in ovo Zn injections increased Zn contents in the embryonic tibia and MT mRNA expression levels in the embryonic liver at E20, however, injections of 150-200 μg Zn/egg were harmful to the embryonic development.