The aim of the study was to evaluate the effect of coumarin and Bacillus cereus derivatives on the productivity and ecology of the caecum of broilers. Assessment of phytochemicals and their synergistic effect with probiotics on the ecological state of individual organs and systems of the body of animals is important for increasing their productivity. The need to address these problems provides sufficient motivation to expand the search for new antimicrobial products. According to the research results, the activity of cellular biomasses to suppress quorum sensing (QS) (Chromobacterium violaceum 026) in Bacillus cereus and a coumarin derivative was revealed. In experiments on animals, i.e. broiler chickens (4 groups, n = 30). Control group: had basic diet (BD); I experimental: was fed with BD + Bacillus cereus probiotic (BC); II experimental: BD + coumarin (CO); III experimental: BD + Bacillus cereus + coumarin (BC + CO). Metagenomic analysis of the bacterial profile of the cecum contents showed the prevalence of representatives of Bacteroidetes phylum in the experimental groups (4.5-15.2%) at 14 days of age, and a decrease in the percentage of Firmicutes phylum (5.9-14.8%), the dominance of Bacteroidaceae families was noted. On the 21st day, a similar increase in representatives of Bacteroidetes phylum (1.7-20.8%), a decrease in Firmicutes and Proteobacteria were noted. At the family level, there is a quantitative change in the microbiome, both in comparison with the control, and with similar data obtained on the 7th day of the experiment. The vast majority belonged to representatives of Bacteroidetes phylum, an increase in bacteria belonging to Firmicutes and Proteobacteria was observed, Rikenellaceae and Ruminococcaceae were minor families. Thus, the additional introduction of Bacillus cereus and a coumarin derivative into the diet of broilers improved the growth parameters and the structure of the intestines of broilers; a positive synergistic effect of Bacillus cereus and coumarin in maintaining the microecological balance of the intestines in poultry was noted.
