Effects of prebiotic supplementation on the concentration of short-chain fatty acids in the ceca of broiler chickens: A meta-analysis of controlled trials

Prebiotics may confer a health benefit to multiple host species (e.g., pigs and humans), probably, in part, through increasing concentration of short-chain fatty acids (SCFAs) in the gut. However, in broiler chickens, a discrepancy of the results among controlled trials exists as to whether prebiotic supplementation can increase concentration of SCFAs in the gut. Therefore, this study was conducted to determine the overall effect size of prebiotic supplementation on the concentration of SCFAs in the ceca of broiler chickens, and to explore sources of heterogeneity of the results among the included studies. The study outcomes were standardized mean difference (SMD) of the concentrations of total SCFAs, acetate, propionate, and butyrate. The relevant citations were retrieved from PubMed, Scopus, and Web of Science. Titles and abstracts of the retrieved citations were screened for possible eligibility. Then, full-texts of eligible articles were assessed for data extraction. A random effects model was used for estimating the overall effect size and for all other meta-analyses. Subgroup meta-analysis was used to assess heterogeneity of the results regarding three sources: type of prebiotics, rearing system, and breed of broiler chickens. Meta-regression analysis was used to determine the association between duration of prebiotic application and SCFA concentrations. Sensitivity analysis was conducted to determine robustness of the results. Risk of bias of the included studies was also assessed. Of 391 citations, 22 studies were included in the meta-analysis. Although prebiotic supplementation significantly increased the concentration of propionate (SMD = 0.29, [95% confidence interval (CI), 0.01–0.56, P = 0.040]) and that of butyrate (SMD = 0.69, [95% CI, 0.37–1.01], P < 0.001), high heterogeneity was observed for the pooled estimate of those outcomes. Types of prebiotics and rearing system were identified as sources of heterogeneity of the results. Some of the included studies remarkably influenced the pooled estimate of the outcomes. In conclusion, more availably related trials are required to confirm a health benefit from prebiotic supplementation on the concentration of SCFAs in broiler chickens.