Dietary Silicon Supplementation Improves Egg Production Performance in Late-Phase Laying Hens: Roles of Antioxidant Capacity, Reproductive Hormones, and Serum Cu/Zn Regulation

Silicon (Si) is an essential trace element involved in multiple physiological processes of animals. This study aimed to investigate the dose-dependent effects of dietary silica (SiO2) supplementation on production performance and key blood parameters in laying hens. A total of 360 hens were randomly assigned to five groups (6 replicates/group, 12 hens/replicate) and fed basal diets supplemented with 0% (control), 0.1%, 0.2%, 0.4%, or 0.8% SiO2 for 8 weeks. Laying performance, egg quality, serum immune indices, reproductive hormone levels, antioxidant status, and serum trace element concentrations were determined. The results showed that dietary SiO2 supplementation significantly affected egg production rate (p < 0.05), with the 0.2% group achieving the highest rate compared to the control. For egg quality, yolk weight and yolk thickness were significantly reduced only in the 0.8% group (p < 0.05), while other parameters were unaffected (p > 0.05). Dietary supplementation with 0.2%, 0.4%, and 0.8% silica significantly increased serum levels of IL-2 and IL-4 (p < 0.05), whereas the 0.8% supplementation decreased IL-1 levels (p < 0.05). Compared with the control group, serum IgA and IgG levels were elevated in the 0.2%, 0.4%, 0.8% silica-supplemented groups (p < 0.05), and serum IgM levels were higher in the 0.4% and 0.8% groups (p < 0.05). Regarding reproductive hormones, dietary SiO2 significantly increased serum concentrations of β-endorphin, estradiol, growth hormone, luteinizing hormone, and progesterone (p < 0.05), with follicle-stimulating hormone elevated in the 0.4% and 0.8% groups (p < 0.05). Dietary silica supplementation did not affect serum activities of SOD, GSH-Px, CAT, or T-AOC. Serum POD activity decreased gradually and was significantly lower in the 0.2%, 0.4%, and 0.8% groups than in the control group (p < 0.05). Furthermore, SiO2 supplementation significantly altered serum Cu and Zn levels (p < 0.05), with the 0.8% group having the highest Ca concentration and the 0.1–0.8% groups showing increased Zn levels compared to the control; no effects on Fe and Mn were observed (p > 0.05). In conclusion, dietary supplementation with 0.2–0.4% SiO2 effectively improves egg production rate, along with enhancing immune function, modulating reproductive hormone secretion, and regulating serum Cu/Zn homeostasis in late-phase laying hens.