Abstract: In ruminants,the rumen is an important digestive and absorptive organ,and a certain amount of degraded nutrients can be directly absorbed across the rumen epithelium and then utilized by the host.Therefore,the development degree of rumen is closely related to the production performance of ruminants,and the well-developed rumen of young ruminants is essential for the optimal performance in adulthood.However,to perform its normal functions,the undeveloped rumen requires a complex transformation process from the non-ruminant phase to the ruminant phase through the extra stimulation,such as solid feed and weaning.At present,how to utilize the developmental pattern of the rumen to conduct the early weaning of young ruminants and concurrently ensure the well-development of the rumen have become one of the urgent problems in the modern ruminant industry.In this paper.The authors summarized the research progress on the evolution of rumen microbiota,rumen histomorphology and metabolic development and its regulation mechanism.Moreover,the authors comprehensively summarized the development rules of rumen from the physiological structure to the function,and clarified the related factors affecting the rumen development and the possible regulation mechanism.This paper aimed to further enrich the theoretical basis related to rumen development,provide theoretical reference for developing nutritional strategies that promote rumen development and tapping the production potential of young ruminants.

Key words: rumen development; microbiota evolution; cell proliferation; ketogenesis