Dual-strain Bacillus subtilis 597 and 600 complex improves productive performance and nutrient digestibility, egg...

Efficacy of a dual-strain Bacillus subtilis complex (597 and 600) on productive performance, egg quality, apparent ileal digestibility (AID), serum parameters, selected cecal bacterial populations, tibia traits, and economic efficiency in laying hens was investigated. A total of 324 Hy-Line Brown hens at 18 wk of age were randomly assigned to two dietary treatments with 18 replicates of 9 birds per cage for a 22-wk trial divided into Phase 1 (wk 18 to 29) and Phase 2 (wk 30 to 40). Diets included a control diet (CON) and CON supplemented with 0.01% probiotic complex (PRO; 1.3 × 10⁶ CFU/g feed). During Phase 1, productive performance was unaffected (P > 0.10). During Phase 2, PRO increased hen-day egg production, egg weight, and mass, with improved feed conversion ratio and egg loss rate (P < 0.05). PRO enhanced eggshell breaking strength, darkened shell color, and reduced yolk cholesterol across both phases (P < 0.01), whereas albumen height, Haugh unit, and shell thickness increased during Phase 2 (P < 0.05). At wk 29 and 40, PRO increased ileal villus height and villus height to crypt depth ratio (P < 0.05). At wk 40, PRO increased the AID of DM, gross energy, CP, Ca, and P (P < 0.05). Serum triglycerides and very low-density lipoprotein cholesterol were lower in PRO across both phases, with lower total cholesterol and corticosterone and elevated serotonin at wk 40 (P < 0.05). Selected cecal bacterial populations showed higher Lactobacillus spp. and Bifidobacterium spp., with reduced Clostridium spp. (P < 0.05) and Escherichia coli (P < 0.001, wk 40). Tibia weight, breaking strength, and Ca content were improved in the PRO at wk 29, with additional improvements in tibia density and ash content by wk 40 (P < 0.05). Economically, PRO increased egg income and return on investment during Phase 2 (P < 0.05). Collectively, dual-strain B. subtilis complex improved hen productive performance, and egg quality by modulating the gut environment and nutrient digestibility.