Ptitsegradskaya, Sergiev Posad-11, Moscow Province, 141300 Russia, e-mail fisinin@vnitip.ru Acknowledgements: Supported by Russian Science Foundation, the project «Modern understanding of gut microflora in poultry depending on feed composition: molecular and genetic approach» ¹ 14-16-00140 A b s t r a c t Currently the processed sunflower products as the cheapest source of vegetable protein are considered an alternative to soybean cake and meal in the poultry diet. <...> However, in sunflower meal the energy value is lower, lysine rate is less than required, and the level of non-starch polysaccharides not digestible in poultry gut because of absence of specific enzymes (i.e., amylases, cellulases, etc.) are rather high. <...> Digestion of these components is possible due to microbial enzymes. <...> Gut content is detained in the poultry caecum for the longest time, wherein the basic processes of microbial proteolysis, and cellulose and starch destruction are performed. <...> Using modern molecular methods of NGS-sequence analysis and real-time PCR, we investigated the number of bacteria and the structure of bacterial community in cecum of 36-day-old Cobb 500 broiler chickens fed with diets containing soybean meal or sunflower meal. <...> Contrary to traditional view, the composition of caecum microbiom was very abundant and divers, and included the obligate gut microflora ( , , , organisms (i.e., enterococcus, bifidobacterium) were minor and the pathogenic bacteria of genera sp., ) and non-identified taxons. <...> Our results first characterized in detail the caecum microbiome as influenced by the combined factors such as specific composition and decreased metabolizable energy in feed. <...> This study showed that the feed containing 25 % sunflower meal caused a 14.7-fold increase in total number of bacteria while the number of phylum amylolytics was 1.4-times lower, the family and cellulosolytics families pressed, respectively, thus indicating limitations in the metabolism of hydrolysable components and cellulose in the poultry gut. <...> Moreover, the obligate bacterial intestinal flora changed in number. <...> Moreover, our research showed that the changes in the cecum bacterial community due to the sunflower meal containing feed depressed the chickens’ performance. <...> Keywords: microflora of cecum, chicken, performance in broilers, bacterial community, NGS-sequencing, real-time PCR. <...> Sunflower processing products in poultry diets as the cheapest source of vegetable protein <...>