Effects of dietary selenium yeast supplementation on the production performance, egg quality, antioxidant and plasma biochemical parameters of laying hens

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.