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The study was conducted to evaluate the effects of increasing inclusion levels of the mixture of Bacillus subtilis and essential oils (BSEO) on production, hatching performance, egg quality, serum antioxidant capacity, immune response, and hormone levels of laying hens. A total of 768 24-wk-old layers were randomly allotted into 4 treatments with 6 replicates of 32 birds each replicate. The experiment lasted for 84 d, and the birds were fed a basal diet (CON) or diets with BSEO at 300 (BSEO-1), 600 (BSEO-2), and 900 mg/kg (BSEO-3) in the other 3 groups, respectively. As the BSEO level increased, egg production (linear, p <.05), yolk index (linear, p <.01), glutathione peroxidase activity (linear, p <.01), total antioxidant capacity (linear, p <.01), oestradiol level (linear, p <.01), the value luteinizing hormone/follicle-stimulating hormone (linear, p <.05) increased in a linear manner. Hatchability (linear and quadratic, p <.01), hatchability of fertile of eggs (linear and quadratic, p <.05), avian influenza virus antibody level (linear, p <.01; quadratic, p <.05), parathyroid hormone level (linear and quadratic, p <.01) in the serum increased linearly and quadratically. Taken together, dietary with BSEO in laying hens could significantly improve egg production, hatchability, and hatchability of fertile eggs, which were associated with an enhancement of antioxidant capacity and the level of AIV-Ab in the serum. This study provided evidence of using BSEO as a potential feed additive for laying hens. Dietary supplementation of BSEO decreased the feed conversion ratio and eggshell thickness of laying hens. Dietary supplementation of BSEO improved the egg weight, fertility, hatchability, hatchability of fertile eggs, and yolk index of laying hens. Dietary supplementation of BSEO enhanced the antioxidant capacity and the level of AIV-Ab in the serum. [ABSTRACT FROM AUTHOR]

To investigate the supplemental effects of Bacillus subtilis C‐3102 on the production, hatching performance, egg quality, serum antioxidant capacity and immune response of laying breeders, a total of 480 Xuefeng black‐bone (25‐week‐old) hens were randomly assigned into four treatment groups: Hens fed the basal diets with 0 (CON), 3.0 × 105 (BS‐1), 6.0 × 105 cfu/g (BS‐2) and 9.0 × 105 (BS‐3) cfu/g of B. subtilis C‐3102. As the B. subtilis C‐3102 level increased, egg weight (linear, p < 0.01; quadratic, p = 0.003), fertility (linear, p = 0.021; quadratic, p = 0.059), hatchability (linear, p = 0.038; quadratic, p = 0.119) and yolk colour (linear, p = 0.006; quadratic, p = 0.021) increased in a linear or quadratic manner. Yolk index increased quadratically (linear, p = 0.054; quadratic, p = 0.017), and eggshell thickness (linear, p = 0.036; quadratic, p = 0.128), the activity of GSH‐Px (linear, p = 0.024; quadratic, p = 0.078), the concentration of IgM (linear, p = 0.016; quadratic, p = 0.056) and the level of AIV‐Ab (linear, p = 0.034; quadratic, p = 0.103) in the serum increased linearly as dietary supplementation of B. subtilis C‐3102 increased. The results showed that dietary treatments did not affect egg production, feed conversion ratio, egg mass, hatchability of fertile eggs, eggshell‐breaking strength, egg‐shape index, yolk percentage, Haugh unit, T‐SOD, T‐AOC, MDA, IgA and IgG concentrations and the level of NDV‐Ab in the serum. In conclusion, dietary supplementation of 9.0 × 105 cfu/g B. subtilis C‐3102 in laying breeders diets may be a feasible means of effectively increasing egg weight, fertility and hatchability, and improving egg quality such as eggshell thickness, yolk index and yolk colour. Besides, B. subtilis C‐3102 can enhance the activity of GSH‐Px, the concentration of IgM and the level of AIV‐Ab in the serum. [ABSTRACT FROM AUTHOR]