Effects of a novel Bacillus subtilis-based probiotic blend on jejunal histomorphology and phylogenetic composition of caecal microbiota in densely stocked broilers
This study investigated the optimal dosage of a novel Bacillus subtilis probiotic blend as a replacement for antibiotic growth promoters by assessing its impact on some gut functionality parameters. In a completely randomized design, 900-day-old Ross 308 broiler chicks were allocated evenly across 36 pens measuring 0.75 meter squared each with 13 birds per pen. Six dietary treatments were randomly assigned to the pens and provided from the starter to the finisher phase. The diets were comprised: 1. a basal broiler diet without AGP or the B. subtilis probiotic mixture (NEGC); 2. the basal diet supplemented with 0.5% (w/w) zinc bacitracin (POSC); and four versions of the basal diet supplemented with B. subtilis probiotic mixture at 0.3 (PRB3), 0.4 (PRB4), 0.5 (PRB5), or 0.6% (PRB6). After slaughter, 5 cm sections of the jejunum were sampled for histomorphological analysis, and caecal digesta from three birds per dietary treatment were collected to assess the phylogenetic composition of the caecal microbiota. There was a significant dietary influence (p < 0.05) observed on jejunal morphology, where broilers on PRB5 exhibited the largest villi absorptive surface area (VASA), while those on PRB6 showed the smallest. A significant dietary effect (p < 0.05) was noted on microbial diversity, but there was no effect (p > 0.05) on alpha-diversity. The caecal microbiota was dominated by phyla Verrucomicrobiota, Bacillota and Asgardarchaeota while genera Akkermansia, Limosilactobacillus, Collinsella, SOKP01, ExiguobacteriumA and Rhizomicrobium were most dominant across and in specific diets. The PRB6 treatment group exhibited the presence of scientifically unknown phylum, SOKP01. Beneficial microbes (i.e., Bacillota and Limosilactobacillus) were most abundant from broilers received diet PRB5 which indicated a healthy gut. Although, Rhizomicrobium require a further investigation for its role in broilers. Moreover, PRB5 improved nutrient uptake as it promoted the largest VASA. Therefore, the four-strain B. subtilis probiotic blend is recommended to be supplemented at 0.5% (w/w) in broiler diet to improve intestinal VASA and microbiota.