Background. The paper presents data on the variability and relationship of microorganisms in the biocenosis of livestock farms. Methods. The analysis of the available literature on the formation, operation, correction, and diagnosis of biocenoses of livestock farms. Results. It is shown that the animal organism is constantly exposed to the environment. A special place among the environmental factors affecting the animal body is microorganisms – causative agents of infectious diseases. Survey available of the literature on the evolution and relationship of microorganisms in different natural habitats. So, in the process of evolution to parasitism in tissues and organs of animals have adapted a variety of microorganisms: viruses, bacteria, fungi, protozoa, helminths, and arthropods. In the nature of a lot of evidence on the phylogenetic relationships of pathogenic microbes from nonpathogenic to the emergence in the evolution of new pathogenic forms of bacteria under favorable environmental conditions and organisms. Conclusion. Recommended livestock farms are to be regarded as ecosystems, artificially created by man. In them, there are special relationships between animals, protozoa, a diverse microflora, which are fundamentally different from those in vivo. In artificial biocenoses, the Association of conditionally pathogenic microorganisms that circulate in the economy can cause various diseases in farm animals.