Necrotic enteritis (NE) is one of the major enterotoxemic diseases in poultry. In vitro and in vivo studies have been performed to determine the effectiveness of Bacillus subtilis (B. subtilis) and mannan oligosaccharides (MOS) in challenged and unchallenged birds with necrotic enteritis. In vitro assays were done to determine the survival ability of B. subtilis in different gastric conditions. It was observed that B. subtilis was able to survive in acidic conditions (P<0.05) and was able to proliferate in 1.5% bile salt concentrations (P>0.05). For in vivo experiment 1 it was noticed that B. subtilis and MOS were able to increase the load of enteric Bifidobacterium animalis, and Lactobacillus reuteri (P<0.05). Reduction in feed conversion ratio and increase in body weight gain was observed in birds fed with B. subtilis (P<0.05). A balance between pro and inflammatory cytokines was observed (P>0.05). In experiment 2 it was observed that there was a decrease in intestinal permeability in birds fed B. subtilis challenged with NE (P<0.05). Increased mRNA levels of zonula occluden (P>0.05) and claudin 1 (P<0.05) was observed in the ileum of the birds fed with B. subtilis. The upregulation of anti-inflammatory and downregulation of pro-inflammatory cytokines was observed in birds fed with B. subtilis and MOS. An increase in IgA antibody levels was observed in the challenged birds with MOS (P<0.05). Our studies found that B. subtilis and MOS were able to increase the proliferation of enteric bacteria. They can be used in the reduction of NE and were able to stimulate the immune responses in birds challenged with NE.
