| Summary: | The broiler chicken industry needs effective probiotics to boost productivity and health. However, published data on the impact of in-feed Bacillus supplementation on physiological parameters in healthy broiler chickens are often conflicting and inconclusive. As a result, this meta-analysis aimed to assess the influence of Bacillus on intestinal histomorphometry (villus height [VH], crypt depth [CD], and VH:CD) and blood immunoglobulin (A, G, and M) levels in healthy broiler chickens. Results were pooled using a random-effects model and presented as Hedges d (d) at 95% confidence intervals (CIs). The results indicate that Bacillus improves gut histomorphometric variables in broilers with the exception of duodenal and ileal CD, which had comparable values with the controls. Likewise, broiler chickens fed Bacillus had increased blood immunoglobulin (Ig) levels compared to controls (IgA: d = 2.29 mg/mL, 95% CI: 1.54–3.04; IgG: d = 2.17 mg/mL, 95% CI: 1.36–2.98; IgM: d = 1.00 mg/mL, 95% CI: 0.54–1.46) taking cognizance of heterogeneity (I
2 = 96–98%). Subgroup analysis showed that studied moderators (Bacillus species, broiler strain, and dosage and duration of supplementation) influenced the results of the meta-analysis. In conclusion, our results suggested that the inclusion of Bacillus at 0.1–6.0 × 106 colony-forming unit/g in broiler chicken feed enhanced the absorptive capacity of the small intestine and blood immunoglobulin levels of broiler chickens. The findings of this study avail important suggestions on policy advancements and sustainable usage of Bacillus in broiler chicken industry.
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