Effect of probiotics on growth performance, cytokine levels, and gut microbiome composition of broiler chickens for 7 and 35 days

Through microbial fermentation, probiotics are essential for improving growth performance and gut health in broiler chickens. This study aimed to assess the effects of three additives on growth performance, cytokine levels, and cecal microbiota in broiler chickens. One-day-old Arbor Acres chicks (total 300) were randomized into four groups: (1) control: basal diet, (2) BS: <italic>Bacillus subtilis</italic> + basal diet, (3) EO: essential oil + basal diet, and (4) BV: <italic>Bacillus velezensis</italic> + basal diet. All chickens were fed and watered ad libitum throughout the experiment. Feed intake and body weight were measured weekly. On days 7 and 35, cecal contents of one bird per replicate, based on average body weight, were collected and analyzed for microbiota using 16S rRNA gene amplicon sequencing. The BS group exhibited enhanced growth performance, including increased final body weight, average daily gain, and reduced feed conversion ratio compared to that of the other groups. On day 7, the BS group exhibited a higher abundance of <italic>Eisenbergiella</italic> (8.24 %), and on day 35, there was an increased abundance of <italic>Firmicutes</italic> (99.63 %) and <italic>Lachnoclostridium </italic>(1.4 %). These results indicate that <italic>B. subtilis</italic> may be a promising probiotic for enhancing broiler health by modulating gut microbiota.