B. Wang, Uchechukwu Edna Obianwuna, Erying Hao, Haijun Zhang, Haihua Zhang, Kai Qiu, Shugeng Wu
This study evaluated the effects of dietary supplementation with soybean isoflavones (SIF) at 30, 50, and 100 mg/kg on reproductive performance, egg quality, ovarian function, tibia quality, serum hormone profile, antioxidant status, and immune function in late-phase laying hens. A total of 432 Hy-Line Brown hens with the average body weight of 2.18 ± 0.12 kg, aged 66 weeks, were randomly assigned to 4 dietary treatments: a basal diet (control) and basal diets supplemented with 30, 50, or 100 mg/kg SIF. The trial lasted for 8 weeks, with each group comprising 6 replicates of 18 birds. Results indicated that SIF supplementation at 30 and 50 mg/kg significantly improved egg production and albumen quality ( P < 0.05). However, no significant differences were observed in eggshell strength and thickness, egg weight, mass, shape index, yolk color, average daily feed intake, and feed-to-egg ratio ( P > 0.05). Dietary SIF linearly increased serum total cholesterol ( P = 0.030) without affecting other biochemical indices. Serum superoxide dismutase activity was significantly upregulated ( P = 0.038), while malondialdehyde levels declined ( P = 0.037). Moreover, hens fed 30 mg/kg SIF showed elevated estrogen levels and an increased number of large white follicles ( P < 0.05). Supplementation with 50 mg/kg SIF increased tibial calcium and phosphorus contents ( P < 0.05). These findings suggest that SIF may serve as a nutritional strategy to improve egg production, egg quality, hormone secretion, bone mineralization, ovarian function, and antioxidant capacity in aged hens. Notably, both 30 and 50 mg/kg inclusion levels produced similar improvements in performance and physiological indices. Therefore, aged laying hens may benefit from dietary SIF at a dose of 30 mg/kg to enhance their reproductive efficiency, owing that such positive effects can be achieved without the need for higher dosage supplementation.