The impact of virginiamicin and probiotics on intestinal microbiome and growth performance traits of chicken (Gallus gallus L.) broilers

Today, there is great interest in the development of environmentally friendly feed additives for poultry farming as a worthy alternative to antibiotics capable of positively modulating the microbiota to control pathogenic microorganisms. However, very few studies have been devoted to comparing the effects of probiotics and antibiotics on the structure of the gut microbiome in broilers. In this study, we compared the composition of the intestinal microbiota and zootechnical parameters in chickens of the Cobb 500 cross during the starter, growth and finishing periods when a probiotic ( Bacillus subtilis in the composition of Cellobacterin®-T) or an antibiotic (Stafac® 110 based on virginiamycin) was added to the diet and showed that the B. subtilis strain accelerates the formation of intestinal microflora. The probiotic also reduces the number of microorganisms of the Campylobacteriaceae family which includes many types of gastroenteritis pathogens, and also increases the digestibility of fiber. T-RFLP analysis and qPCR method were used to assess changes in the intestinal microbiota of Cobb 500 broiler chickens fed a Bacillus subtilis -based dietary probiotic and virginiamycin-based dietary antibiotic Stafac® 110. On day 14, the total counts of cecal bacteria, as compared to control, were 9.1 times higher (p ≤ 0.05) in broilers fed Stafac® 110, and 54.2 times higher (p ≤ 0.001) when fed B. subtilis preparation. This indicates rapid microbial colonization of gastrointestinal tract of the chickens fed Stafac® 110 and B. subtilis . T-RFLP analysis revealed two dominant cecal phyla, Firmicutes and Proteobacteria , while phyla Actinobacteria , Bacteroidetes , and Fusobacteria were less abundant. The taxa are detected which ferment non-starch polysaccharides to produce short-chain fatty acids, inhibit the competing pathogens due to production of bacteriocins, and acidize the chyme as synthesize organic acids. Administration of the dietary antibiotic mostly positively influences the cecal microbiota, e.g., the cellulolytic bacteria and Clostridia forms involved in the synthesis of organic acids became more abundant (p ≤ 0.05). Similar beneficial effects, e.g., an increase in Clostridia counts (p ≤ 0.05) compared to control, occurred when the probiotic strain was administered. On day 14 of rearing, the dietary antibiotic and probiotic reduced abundance of Campylobacteriaceae family comprising gastroenteritis pathogens (p ≤ 0.05) when compared to control. An increase in bodyweight as compared to control (from 1845.8±20.9 to 1936.4±17.9 g, p = 0.046) occurred in 36-day-old chickens fed Stafac® 110 but not the probiotic strain but not the probiotic strain, despite recovery of gut microbiota in the chickens fed B. subtilis. A 7.1 % increase in fiber digestibility (p = 0.0027) occurred in broilers fed dietary probiotic and a 2.3 % increase (p = 0.047) in those fed the dietary antibiotic, which may be due to the action of cellulolytic microorganisms. Therefore, a dietary B. subtilis -based probiotic which promotes recovery of gut microbiota and increases fiber digestibility in feeds for broiler chickens can be an effective alternative to the virginiamycin-based antibiotic Stafac® 110.