Efficacy of Bacillus subtilis to replace in-feed antibiotics of broiler chickens under necrotic enteritis-challenged experiments: a systematic review and meta-analysis

Abstract

Necrotic enteritis (NE) and coccidiosis are among the most prevalent infectious diseases in broiler chickens, contributing to large profitability losses. Bacillus subtilis is a promising direct-fed probiotic to counter various pathogens infection in broiler chickens. Here, we performed a meta-analysis to investigate the effects of B. subtilis on broiler chickens performance. A total of 28 studies were selected according to a PRISMA checklist. Random-effect model and mixed-effect model of meta-analysis were fitted to estimate the overall effects of B. subtilis (BS) treatment compared to either the control group (CON) or NE-infected group (NE_inf) as a baseline. Hedges' g effect size and its variance were used as estimators of standardized mean difference (SMD) calculation where the results were presented at a 95% confidence interval (95% CI) of the SMD. Overall, NE_inf broiler chickens depressed (P < 0.01) body weight (BW), average daily gain (ADG), and feed intake, and elevated (P < 0.01) feed conversion ratio (FCR). Treatment with BS improved ADG and final BW of NE_inf with no difference (P = 0.15) between BS and antibiotics (AB), indicating that they had comparable efficacy to treat NE in broiler chickens. BS supplemented to uninfected CON (BSS) improved (P < 0.01) final BW, ADG, and FCR. Compared to CON, BS, and AB failed to recover the FCR but these treatments decreased (P < 0.01) FCR when compared to the NE_inf group with similar efficacy (P = 0.97). As expected, NE_inf birds had a higher mortality rate (P < 0.01) and higher lesion score (P < 0.01) compared to CON, and treatment using AB and BS successfully decreased (P < 0.01) the mortality rate and lesion score. Compared to BS, AB was more effective to lower (P = 0.01) mortality rate, but comparable (P = 0.65) to minimize lesion score. To conclude, B. subtilis could be an effective natural additive to replace in-feed antibiotics in broiler chickens challenged with C. perfringens. However, the efficacy to reduce mortality rate was better with antibiotics treatment.

Keywords: Clostridium perfringens; Eimeria; alternative antibiotics; antimicrobial resistance; probiotics.

Figure 1

Flowchart of article selection based on PRISMA protocol.

Figure 2

Traffic light plots and weighted bar plots represent the results of risks of bias assessment studies included in the meta-analysis (green means low risk of bias, yellow means unclear risk of bias, red means high risk of bias).

Figure 3

Funnel plots to assess the publication bias of the studies. Egger's test results were included in each outcome of the plot.

Figure 4

Forest plot of BW showing the 95% CI (lower–upper) of the SMD between the means of groups of dietary treatment and group of control diet. The x-axis shows the SMD; central-dashed line represents the zero effect (SMD = 0) of dietary interventions; blue-diamonds represent the overall effect while the specific symbols in each line represent the SMD (subgroup effect) of the specific group. Reduction effects are reflected when the SMDs are on the left of the central dashed-line and increasing effects are in opposite (to the right of the line).

Figure 5

Forest plot of ADG showing the 95% CI (lower–upper) of the SMD between the means of groups of dietary treatment and group of control diet. The x-axis shows the SMD; central-dashed line represents the zero effect (SMD = 0) of dietary interventions; blue-diamonds represent the overall effect while the specific symbols in each line represent the SMD (subgroup effect) of the specific group. Reduction effects are reflected when the SMDs are on the left of the central dashed-line and increasing effects are in opposite (to the right of the line).

Figure 6

Forest plot of FI showing the 95% CI (lower–upper) of the SMD between the means of groups of dietary treatment and group of control diet. The x-axis shows the SMD; central-dashed line represents the zero effect (SMD = 0) of dietary interventions; blue-diamonds represent the overall effect while the specific symbols in each line represent the SMD (subgroup effect) of the specific group. Reduction effects are reflected when the SMDs are on the left of the central dashed-line and increasing effects are in opposite (to the right of the line).

Figure 7

Forest plot of FCR showing the 95% CI (lower–upper) of the SMD between the means of groups of dietary treatment and group of control diet. The x-axis shows the SMD; central-dashed line represents the zero effect (SMD = 0) of dietary interventions; blue-diamonds represent the overall effect while the specific symbols in each line represent the SMD (subgroup effect) of the specific group. Reduction effects are reflected when the SMDs are on the left of the central dashed-line and increasing effects are in opposite (to the right of the line).

Figure 8

Forest plot of mortality rate showing the 95% CI (lower–upper) of the SMD between the means of groups of dietary treatment and group of control diet. The x-axis shows the SMD; central-dashed line represents the zero effect (SMD = 0) of dietary interventions; blue-diamonds represent the overall effect while the specific symbols in each line represent the SMD (subgroup effect) of the specific group. Reduction effects are reflected when the SMDs are on the left of the central dashed-line and increasing effects are in opposite (to the right of the line).

Figure 9

Forest plot of lesion score showing the 95% CI (lower–upper) of the SMD between the means of groups of dietary treatment and group of control diet. The x-axis shows the SMD; central-dashed line represents the zero effect (SMD = 0) of dietary interventions; blue-diamonds represent the overall effect while the specific symbols in each line represent the SMD (subgroup effect) of the specific group. Reduction effects are reflected when the SMDs are on the left of the central dashed-line and increasing effects are in opposite (to the right of the line).