Abstract
Bacillus subtilis (B. subtilis) as in-feed probiotics is a potential alternative for antibiotic growth promoters (AGP) in the poultry industry. The current study investigated the effects of B. subtilis on the performance, immunity, gut microbiota, and intestinal barrier function of broiler chickens. A 42-day feeding trial was conducted with a total of 600 1-day-old Arbor Acres broilers with similar initial body weight, which was randomly divided into one of five dietary treatments: the basal diet (Ctrl), Ctrl + virginiamycin (AGP), Ctrl + B. subtilis A (BSA), Ctrl + B. subtilis B (BSB), and Ctrl + B. subtilis A + B (1:1, BSAB). The results showed significantly increased average daily gain in a step-wise manner from the control, B. subtilis, and to the AGP groups. The mortality rate of the B. subtilis group was significantly lower than the AGP group. The concentrations of serum immunoglobulin (Ig) G (IgG), IgA, and IgM in the B. subtilis and AGP groups were higher than the control group, and the B. subtilis groups had the highest content of serum lysozyme and relative weight of thymus. Dietary B. subtilis increased the relative length of ileum and the relative weight of jejunum compared with the AGP group. The villus height (V), crypt depth (C), V/C, and intestinal wall thickness of the jejunum in the B. subtilis and AGP groups were increased relative to the control group. Dietary B. subtilis increased the messenger RNA (mRNA) expression of ZO-1, Occludin, and Claudin-1, the same as AGP. The contents of lactic acid, succinic acid, and butyric acid in the ileum and cecum were increased by dietary B. subtilis. Dietary B. subtilis significantly increased the lactobacillus and bifidobacteria in the ileum and cecum and decreased the coliforms and Clostridium perfringens in the cecum. The improved performance and decreased mortality rate observed in the feeding trial could be accrued to the positive effects of B. subtilis on the immune response capacity, gut health, and gut microflora balance, and the combination of two strains showed additional benefits on the intestinal morphology and tight junction protein expressions. Therefore, it can be concluded that dietary B. subtilis A and B could be used as alternatives to synthetic antibiotics in the promotion of gut health and productivity index in broiler production.
Highlights
Antibiotics have been widely used as a growth promoter and to enhance the immunocompetence of birds against infectious diseases [1]
A total of 600 newly hatched male Arbor Acres (AA) broiler chicks with an average body weight (BW) of 40.09 g were obtained from a local hatchery and assigned into five dietary treatments in a randomized complete block design with 10 replicates per treatment
On days 14 and 28, the BW of the birds fed with antibiotic growth promoter (AGP) was significantly higher (P ≤ 0.05) than those fed with the control and B. subtilis diets
Summary
Antibiotics have been widely used as a growth promoter and to enhance the immunocompetence of birds against infectious diseases [1]. The global trend in animal production is toward a reduction or ban on the use of feed antibiotics for growth [antibiotic growth promoter (AGP)] and an increase in the application of non-antibiotic approaches that can provide similar benefits. This is accrued to the fact that the widespread use of antibiotics over 50 years has led to the emergence of resistant bacteria and drug residues in animal products [2,3,4]. It has been reported that the effects of dietary B. subtilis supplementation on growth performance and intestinal physiology in broilers were markedly strain-dependent [17, 18], the need for continuous studies on the various strains of B. subtilis to understand their mechanisms of action in these animals
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