Abstract: There are many microorganisms in the gastrointestinal tract of ruminants,such as bacteria,fungi,protozoa and archaea.Gastrointestinal microbes play an important role in the energy metabolism and central nervous system of animals.Intestinal microbes can be in direct contact with intestinal cells,producing not only metabolites that activate the endogenous central nervous system signaling mechanisms,but also independently producing or contributing to the production of many neurally active molecules.Microbial metabolites and neuroactive molecules form a complex reflex network through key pathways such as neural signaling pathways,gastrointestinal endocrine signaling pathways and immune systems.That is,gastrointestinal microorganisms and metabolites conduct signals to the central nervous system through the afferent neurons.The gastrointestinal microbes interact with the host through the main signaling pathways,affecting the body's gastrointestinal barrier,nutrient metabolism,immune response and other physiological functions and feeding behavior.The article mainly focuses on the gastrointestinal microbial species of ruminants,the "bottom-up" transmission pathway of microorganisms through the gut-brain axis,and the role of microorganisms and their metabolites in host diseases and behavior through the gut-brain axis.The possible influencing factors of gastrointestinal microbial-gut-brain axis were analyzed,and the research on the axis of ruminants is prospected in this paper.

Key words: ruminants; gastrointestinal microorganism; gut-brain axis; metabolites; transmitssion signals