Meta-Analysis of Probiotic Effects on Broiler Performance: Bacillus Outperforms Lactobacillus with Enhanced and Longer Efficacy in Developing Regions

Probiotics are increasingly investigated as sustainable alternatives to antibiotic growth promoters in poultry production, with Bacillus and Lactobacillus being the most extensively studied genera. However, performance responses remain inconsistent across studies, probiotic genera, and production settings. This meta-analysis quantified the overall effects of probiotics on broiler growth performance, with particular emphasis on genus-specific responses and study-level moderators of feed conversion ratio (FCR) . Following PRISMA guidelines, 53 studies comprising 106 independent trials were included. Random-effects models were used to estimate mean differences, and heterogeneity was assessed using Q, τ², and I² statistics. Meta-regression and subgroup analyses evaluated potential moderators, including probiotic genus, dose, trial duration, breed, feed type, probiotic configuration, and regional economic status. Publication bias was assessed using funnel plots and adjusted using the Duval and Tweedie trim-and-fill method. Overall, probiotic supplementation significantly improved body weight (66.61g, P < 0.001), feed intake (29.80g, P =0.002), and FCR (0.058, P < 0.001). After adjustment estimates increased for body weight (78.34g), feed intake (61.42g), and FCR (0.107). Probiotic genus, trial duration, and regional economic classification were identified as significant moderators of FCR ( P < 0.05). Subgroup analyses indicated that Bacillus -based probiotics were associated with more consistent improvements in FCR across production stages (days 21, 35, and 42), whereas Lactobacillus -based effects showed a transient effect limited to day 21. Probiotic-associated improvements in FCR were more pronounced in studies conducted in developing regions. Overall, the findings support that probiotics enhance broiler performance, with Bacillus providing superior and sustained efficacy, supporting its strategic use as an alternative to antibiotic growth promoters.