Effect of the Inclusion of Bacillus spp. in Growing–Finishing Pigs’ Diets: A Meta-Analysis

SIMPLE SUMMARY: Dietary probiotics are an alternative to antibiotic inclusion in pigs, the modulation of the intestinal environment, the inhibition of pathogen’s colonization by an increase in microbial competition in the gastrointestinal tract, and the regulation of mucosal immunity. These factors can lead to improvements in animal’s health and, therefore, productivity. The objective of this study was to use a meta-analysis approach to ascertain the effect of Bacillus spp. on growth performance of growing–finishing pigs and then to assess causes for the heterogeneity of responses detected using meta-regression. Overall, the inclusion of Bacillus spp. (median 486 mg/d) in growing–finishing pigs can increase the average daily gain (ADG) and decrease the feed: gain ratio (F:G). ABSTRACT: This meta-analysis determined the effect of Bacillus spp. on growth performance of growing–finishing pigs and then assessed causes for the heterogeneity of responses detected using meta-regression. A database of 22 articles published from 2000 to 2020 was identified, and 9 articles fitted the selection criteria and were integrated in the final database. Statistical analysis was performed to analyze the effect size for ADG, average daily feed intake (ADFI), and F:G ratio using a standardized means difference (SMD) at a 95% confidence interval. A meta-regression analysis was used to investigate the cause of heterogeneity, using the individual SMD for each study assessment as the outcome and the associated SE as the measure of variance. Dietary Bacillus spp. supplementation had no effect on ADFI (SMD: −0.052, p = 0.138) and numerically increased ADG (SMD: 0.113, p = 0.081) and reduced the F:G ratio SMD: −0.127, p < 0.001). Meta-regression outcomes suggested that the number of animals per group was an essential component promoting heterogeneity in ADG. Overall, the inclusion of Bacillus spp. (median 486 mg/d) in growing–finishing pigs can increase ADG and can decrease the F:G ratio.