Two crucial characteristics of livestock farming are feed efficiency (EA) and enteric methane (ME) emission from animals. Studies using different omics technologies have reported that the rumen microbiota can promote phenotypic variations in the host in the short and long term. There are many possible theories for interspecies communication between microbiota and host cells, such as through proteins, RNA, and metabolites, which can be transported throughout the host body via extracellular vesicles (EVs). Small non-coding RNAs (sRNAs), such as microRNAs (miRNAs), represent promising candidates for a "common language" across species, as they are produced by all living organisms and can be transported throughout the host body by EVs. Recent studies suggest that miRNAs can regulate bacterial gene expression and thus influence the composition of the microbiome. Furthermore, observations from studies support the existence of RNAs in prokaryotic organisms similar to miRNAs (msRNAs), capable of regulating host gene expression. The hypothesis for this project is that the host can regulate its microbiota through the action of regulatory elements (such as miRNAs) and the interaction between genes, just as microorganisms can regulate various host metabolic pathways through msRNA and specific proteins.A second hypothesis to be considered is that EVs may transport these primary mediators in microbiota-host communications. The main objective of this study is to investigate the interaction and molecular regulation between hosts and microorganisms associated with feed efficiency and methane emission in cattle, as well as to investigate the presence of miRNAs and msRNA transported by extracellular vesicles that could be used for therapeutic purposes and for improving the characteristics of livestock.