Currently, dysbiosis, rupture of the intestinal barrier and inflammation have become concerns of industrial poultry, since they culminate in the physiological and productive impairment of birds. The objective was to discuss the role of the intestinal microbiota of birds in animal development, as well as to highlight the benefits and/or losses caused by these microorganisms. The methodology adopted was a descriptive study, with a bibliographic review of scientific papers published in different indexed bases, with a time frame of the last decades. It was found that the use of sequencing the RNA ribosomal gene (rRNA) 16S is an important tool to identify and enumerate the intestinal bacteria present in production birds. Regarding the composition of the microbiota, in the small intestine there are mainly Lactobacillus, Streptococcus, Enterococcus, Bifidobacterium, Bacterioides, Clostridium, Fusobacterium and coliforms. In the large intestine, Lactobacillus, Bacterioides, Proteobacteria, Bacillus, Clostridium and Bifidobacterium. In the small intestine, bacteria participate in metabolism by improving nutrient absorption, hydrolyze polysaccharides to produce short-chain fatty acids, which will be absorbed and participate in important metabolic pathways in the supply of carbon and energy sources to birds. Despite the benefits of the microbiota in promoting a stable intestinal environment, in unfavorable situations, such as inadequate breeding, it can act as pathogens, produce toxic metabolites and impair the productive performance of birds.

The poultry industry evolved and reached high production performance, with several zootechnical techniques that contributed to the current scenario, including ambience, genetics and diet - all contributing and optimizing the digestive system of the birds. The gastrointestinal tract is a system with several functions and attributions within the organism, among them, digestion of the host, immunity and proper functioning of the system. The gut microbiota has direct effects on metabolic processes and subsequently on the performance of birds. Issues related to microbiota have acquired relevance both for the maintenance and modulation of these microorganisms. One of the maneuvers used to manipulate the intestinal microflora was the use of antibiotics, acting as growth promoters; however, this type of additive, due to sanitary pressure, should be abolished in the coming years, which makes other options appear on the scene, among them, phytogenic additives. Among the latter, essential oils have gained prominence for their beneficial activity in the microbiota as well as their natural composition and non-residual impacts on the process. Based on this, the aim was to review the guidelines that affect the intestinal microbiota in poultry.

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