Effect of Bacillus subtilis and Oregano Oil on Performance, Gut Microbiome, and Intestinal Morphology in Pullets

SIMPLE SUMMARY: Supplementation with additives, such as Bacillus subtilis and oregano oil, has a positive impact on the poultry health and performance by promoting the development and diversity of cecal microbial communities. Here, we observed changes in feed conversion ratio, gut morphology, and cecal microbial composition when we had a basal diet supplemented that Bacillus subtilis and oregano oil in pullets. The results showed that Bacillus subtilis and oregano oil had no effect on weight change, but they had a positive effect on gut morphology. They also had a positive effect on the microbial changes in the cecum. ABSTRACT: This study aimed to examine the effect of probiotics containing Bacillus subtilis and oregano essential oil on the growth performance, intestinal morphology, and cecal microbial composition in pullets aged 0–18 weeks. A total of 324 day-old Hy-Line Brown chicks were randomly assigned to three treatment groups, with six replicates per group and 18 birds per pen. The experimental treatments consisted of the following: a control group receiving a basal diet (Con), a group receiving a basal diet supplemented with 1 g/kg (3 × 10(8) cfu/kg) of Bacillus subtilis (BS), and a group receiving a basal diet supplemented with 0.3 g/kg of oregano essential oil (ORO). The groups supplemented with BS and ORO demonstrated significantly higher villus height/crypt depth ratios than the Con group. Microbial richness was significantly higher in groups supplemented with BS (p = 0.0317) and ORO (p = 0.00794) than in the Con group. These findings revealed a distinct separation between gut microbial communities of the Con group and those supplemented with ORO, based on unweighted and weighted UniFrac indices. Therefore, supplementation with Bacillus subtilis and oregano oil improved the composition of the microbiota, suggesting their positive effects on the gut health of pullets.