The present study aimed to optimize the combined effect of dietary selenium (SE) and iodine (ID) on the productive and reproductive performance and antioxidant capacity of Longyuan breeding ducks. A total of 288 Longyan duck breeders aged 20 wk were randomly assigned to four groups with six replicates (n = 72 ducks/group
12 ducks/replicate). A 2 × 2 factorial arrangement experiment was performed and included 2 supplementation levels of each SE and ID for 200 days of the experimental period. The first group (SE0/ID0) received a basal diet without SE or ID supplementation and was considered to be the control group, whereas the other three groups, SE0/ID4, SE2/ID0 and SE2/ID4, received a basal diet supplemented with 0.4 mg ID/kg, 0.2 mg SE/kg or 0.2 mg SE supplemented with 0.4 mg ID/kg, respectively. The results indicated that the albumin height of the SE2/ID0 group was lower (P <
0.05) than that of the control group, that the egg shape index of the SE2/ID4 and SE0/ID4 groups were lower (P <
0.05) than that of the control group (SE0/ID0), and that the SE concentration significantly increased (P <
0.05) in the SE2/ID0 and SE2/ID4 groups. Hatchability and embryonic mortality improved (P <
0.05) in the SE2/ID0 group. Plasma GSH-Px activity was increased (P <
0.05) by reducing the concentration of malondialdehyde (MDA) in the SE groups. In addition, the tibia length significantly increased (P <
0.05) in the ID (SE0/ID4 and SE2/ID4) groups compared with that in the control group, the plasma content of IGF-1 in the SE2/ID4 and SE0/ID4 groups were greater (P <
0.05) than that in the control group, and the bone mineral content increased (P >
0.05) in the SE2/ID0 and SE0/ID0 groups. Compared with those in the other groups, the mRNA expression of antioxidant-related genes, including Nrf2 and SHMT1 in the SE2/ID4 group was upregulated (P >
0.05), especially in the SE2/ID4 group. Overall, dietary treatment with SE2/ID4 (0.2 mg SE in 0.4 mg ID/kg diet) could be a suitable feed supplement for improving the the egg quality, health status, endogenous antioxidant content, antioxidant-related gene expression and pre-hatching quality of Longyuan duck breeders.