Effects of dietary probiotic supplementation on growth performance and intestinal morphology in broiler chickens: a meta-analysis

This meta-analysis evaluated the effects of probiotic supplementation on growth performance and intestinal morphology in broiler chickens. Following the PRISMA 2020 statement, 19 peer-reviewed studies published between 2011 and 2025 were identified from Web of Science and PubMed. Data were pooled using DerSimonian–Laird random-effects models, with mean differences (MD) and 95% confidence intervals (CI) reported. Probiotic supplementation increased average daily gain (MD = 1.53 g/d, 95% CI: 1.17 to 1.89) and average daily feed intake (MD = 1.15 g/d, 95% CI: 0.52 to 1.79) and reduced feed conversion ratio (MD = −0.04 g/g, 95% CI: −0.05 to −0.03, P < 0.001). Villus height and villus height-to-crypt depth ratio increased in the duodenum, jejunum, and ileum, while crypt depth decreased in the jejunum and ileum. Substantial heterogeneity was observed across outcomes ( I 2 = 94.70%−99.40%), and most 95% prediction intervals included zero. HKSJ sensitivity analyses retained the significant effects on growth performance, whereas the reduction in jejunal crypt depth was no longer significant. Exploratory subgroup analyses indicated differences in responses according to strain number and the genus of probiotics. In conclusion, probiotics have promising potential to improve growth performance and intestinal morphology in broilers.