The impact of Bacillus subtilis DSM 32315 on the pathology, performance, and intestinal microbiome of broiler chickens in a necrotic enteritis challenge

It was hypothesized that dietary inclusion of Bacillus subtilis DSM 32315 could inhibit Clostridium perfringens induced necrotic enteritis (NE), thereby improving broiler performance. Male, d 0 chicks were randomly assigned 14 birds/pen, 11 pens/treatment in 3 treatments: a basal diet (control), a coccidiostat fed control (Narasin), and a direct fed microbial (DFM) B. subtilis DSM 32315 treatment. Necrotic enteritis was induced in all birds by oral inoculation of Eimeria maxima oocysts on d 12 and a virulent C. perfringens on d 16. Mortality was reduced (P < 0.001) in DFM and Narasin compared to control. DFM reduced (P < 0.001) feed conversion ratio (FCR) compared to control. Furthermore, DFM and Narasin reduced (P < 0.001) footpad lesions. The DFM was shown to increase (P < 0.05) Bacillus spp. and decrease (P < 0.05) C. perfringens in the ileum and cecum at several time points. To investigate microbiome changes in the cecum, digesta samples were analyzed with %guanine and cytosine (%G+C) microbial profiling which fractionates bacterial chromosomes based on the %G+C in DNA. The method revealed treatment profile peaks in low (27.0 to 34.5%), mid (40.5 to 54.0%), and high (59.0 to 68.0%) G+C fractions. 16S rRNA gene amplification and high throughput sequencing was conducted on each of these fractions in order to elucidate specific bacterial population differences. In the low and mid %G+C fractions, DFM had greater abundance of Lactobacillaceae family members (P = 0.03 and P = 0.01, respectively) and Lactobacillus salivarius (P = 0.04 and P = 0.01, respectively) than control or Narasin. Lactobacillus johnsonii was also greater in the low %G+C fraction compared to control and Narasin (P = 0.01). Lachnospiraceae (P = 0.04) and Ruminococcaceae (P < 0.01) in the mid %G+C fraction were reduced in the DFM compared to control. Positive alterations to the microbial populations in the gut of broilers may at least be a partial mechanism by which B. subtilis DSM 32315 reduced pathology and improved performance of broilers in the NE challenge.