_1785384738 20260730041218000 Rovedar Daryoushbabazadeh@gmail.com Rovedar Journal of World’s Poultry Science J. World's Poult. Sci. 2980-7999 06 29 2026 5 2 Sajjad Hassan Qadeer https://orcid.org/0009-0007-3891-7171 Introduction: Probiotics represent the most extensively investigated strategy for maintaining broiler performance under antibiotic-free conditions. The present study aimed to quantify the effects of dietary probiotic supplementation on body weight gain, average daily gain (ADG), feed conversion ratio (FCR), feed intake, intestinal morphology, gut microbiota composition, and short-chain fatty acid (SCFA) production in broiler chickens.Materials and methods: Web of Science and Scopus databases were searched, yielding 1,728 unique records after deduplication. Multi-stage systematic screening identified 26 original experimental studies with extractable full-text numerical data meeting all pre-specified inclusion criteria. Studies were classified according to probiotic genus, including Bacillus spp., Lactobacillus, Saccharomyces cerevisiae, Enterococcus faecium, Clostridium butyricum, strain complexity, dose, and feeding duration. Results: Probiotic supplementation consistently improved growth performance, as documented by all 26 studies. The pooled weighted mean differences (WMDs) for FCR was −0.076 across 14 studies, indicating a mean 4.9% reduction in FCR compared with groups that received only a basal diet without probiotics. Pooled WMD for ADG was +3.85 g/d in eight studies. Villus height was significantly increased in all six studies that reported morphological data, yielding a pooled WMD of +253.6 μm. One study found that a compound probiotic containing Enterococcus faecium, Bifidobacterium, and Pediococcus acidilactici significantly increased final body weight from 2,422.50 ± 19.08 g to 2,589.41 ± 13.10 g, accompanied by concurrent increases in cecal butyrate and propionate levels. In a separate study, Bacillus subtilis supplementation significantly increased villus height from 800.93 to 1,423.10 μm at 28 days of age in Cobb broiler chickens. Across six studies reporting microbiota data and four reporting SCFA outcomes, probiotics consistently increased Lactobacillus abundance, reduced Escherichia coli, Salmonella, and Clostridium perfringens counts, and elevated SCFA concentrations. Conclusion: Dietary probiotic supplementation significantly improved FCR, ADG, villus height, and gut microbiota balance in broiler chickens. Bacillus-based and compound multi-strain formulations demonstrated the strongest and most consistent effects in broiler chickens. 06 29 2026 17 27 https://creativecommons.org/licenses/by/4.0 10.58803/jwps.v5i2.128 https://jwps.rovedar.com/index.php/JWPS/article/view/128 https://jwps.rovedar.com/index.php/JWPS/article/download/128/130 https://jwps.rovedar.com/index.php/JWPS/article/download/128/130 Food and agriculture organization corporate statistical database (FAOSTAT). Statistical database: Livestock primary — production quantity, chicken meat. Rome: Food and Agriculture Organization of the United Nations; 2024. Available at: https://www.fao.org/faostat/en/#data/QCL 10.3382/ps.2007-00249 Food and agriculture organization of the United Nations/ World health organization (FAO/WHO). Guidelines for the evaluation of probiotics in food. Probiotics in food. Health and nutritional properties and guidelines for evaluation. Rome: Food and Agriculture Organization of the United Nations, World Health Organization; 2006. Available at: https://www.fao.org/3/a0512e/a0512e.pdf 10.3389/fmicb.2022.1088179 10.1016/j.aninu.2025.04.011 10.1016/j.psj.2026.106587 10.1007/s12602-024-10314-3 10.3382/ps/pey602 10.1515/biol-2021-0031 10.1016/j.psj.2026.106447 10.1371/journal.pone.0085347 10.1136/bmj.n71 10.3389/fmicb.2023.1255894 10.1016/j.psj.2025.105611 10.1080/1828051X.2022.2148577 10.3389/fvets.2026.1776015 10.1016/j.psj.2025.105795 10.12681/jhvms.30488 10.1016/j.vas.2021.100216 Bishehkolaei R, Rezaeipour V, Abdullahpour R, Jarrahi M, Ghasemi H, Daryaei S, et al. Milk kefir as a natural probiotic, individually or in combination with organic acids in broiler chickens: Influence on immune-related gene expression, intestinal morphology, microbiota activity, and serum biochemistry. Poult Sci J. 2021; 9(1): 97-105. DOI: 10.22069/psj.2021.18783.1665 10.1093/jas/skae183 10.3390/ani11051245 10.1186/s12917-024-03960-w 10.1111/jpn.13784 10.5398/tasj.2021.44.1.39 10.1016/j.psj.2025.105743 10.1038/s41598-026-42376-4 10.1016/j.psj.2023.103400 10.1016/j.micpath.2025.107859 10.1080/09712119.2020.1804916 10.3389/fphys.2021.737481 10.1016/j.psj.2025.105417 10.1080/09712119.2020.1754218