Abstract
This study was designed to evaluate the effects of dietary selenium yeast (SY) supplementation (0.3-0.9 mg/kg Se) on key production performance parameters, egg quality traits, antioxidant capacity, and plasma immune indices in laying hens, with concurrent verification of the safety profile of the upper test dose. A total of 108 healthy Hy-Line Brown laying hens (162 days old, weighing 1.61 ± 0.05 kg) were randomly allocated to four treatment groups, each comprising three replicates of nine birds. Following a 10-day acclimatisation period, a 60-day feeding trial was conducted. Dietary SY had no significant impact on core production metrics (all P > 0.05) but improved egg quality in a time and dose-dependent manner under the present experimental conditions: eggshell thickness, albumen height, and Haugh units were elevated in linear/quadratic patterns (P < 0.05), with the most pronounced effects observed in the 0.9SY treatment. SY supplementation increased the selenium content in eggs (0.32-0.977 mg/kg) and plasma (0.15-0.42 mg/L) of laying hens in a dose-dependent manner (linear trends, P < 0.05), with all SY groups meeting the Chinese standard for selenium-enriched eggs (GH/T1135-2017; ≥0.15 mg/kg). Antioxidant capacity was enhanced in a tissue-specific manner: hepatic activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), alongside plasma total antioxidant capacity (T-AOC), were elevated linearly and/or quadratically (P < 0.05), while yolk malondialdehyde (MDA) concentrations were reduced by Day 60 (linear/quadratic P < 0.05). SY exerted selective immunomodulatory effects: plasma concentrations of interleukin-6 (IL-6) and immunoglobulin M (IgM) decreased in linear and/or quadratic trends (P < 0.05), immunoglobulin G (IgG) tended to increase linearly (0.05 < P < 0.10), and immunoglobulin A (IgA) remained unaltered (P > 0.05). Critically, the 0.9 mg/kg Se dose-exhibiting the most favourable outcomes across all measured endpoints-remained within the dietary Se safety threshold (≤ 1.0 mg/kg) established by the National Research Council (NRC, 1994), in the absence of overt toxicological manifestations. In conclusion, under the parameters of this 60-day trial, dietary SY supplementation safely enhances egg quality, antioxidant defence, and immune homeostasis in laying hens, with 0.9 mg/kg Se emerging as the optimal dose. These findings support the potential utility of SY as a functional feed additive for selenium-enriched egg production in analogous commercial production systems.