Abstract: Probiotics are defined as live microorganisms that confer a health benefit on the host（human/animals）,including bacteria,fungi（i.e.,yeasts）,etc. Probiotics demonstrate beneficial effects on the animal by improving the growth and immunity,and therefore have been proposed to be a promising alternative to antibiotics. It is suggested that the interaction between probiotics and gut microbiota results in the beneficial effect of probiotics,despite that the mechanisms remain largely unknown. This review summarizes the most recent advances in regulating microbiota in gastrointestinal tract of early age livestock（piglet,chicken,and ruminant）by probiotics based on high-throughput sequencing technology. The paper also highlights the future directions,including how probiotics interact with gut microbiota and affect their functions,how probiotics affect gut microbiota of livestock under different health conditions in early age,and how host factors affect the efficacy of probiotics in terms of regulating gut microbiota of livestock in early age.

Key words: probiotics, mechanism, microbiota in gastrointestinal tract, livestock, early age