<p>Mulberry leaves, a traditional Chinese medicine with the values of medicine and food, are rich in various active ingredients and nutrients. Gastrointestinal bacteria are recognized to play a crucial role in food digestion, nutrient metabolism and the host immune health. However, the modulations of mulberry leaves on microbiota and metabolites remain insufficiently understood. In this study, a feeding experiment was conducted involving three groups on growing mutton sheep: one fed with dried mulberry leaves, another with fermented mulberry leaves and one without mulberry leaves (as control), afterwards, 16s sequencing of ruminal and fecal microbiota was performed. The present study revealed that the addition of mulberry leaves significantly modifies rumen bacterial community and promote the production of volatile fatty acids, which in turn promotes rumen digestion and metabolism of growing mutton sheep to ensure the supply of nutrients and promote immune health. Furthermore, mulberry leaves supplementation helps regulate the fecal microbial community and reduce the emission of odorous gas (hydrogen sulfide and harmful Benzene, 1, 2, 3, 5-tetramethyl). Unexpectedly, feeding with fermented mulberry leaves could reduce the emission of fecal smelly or harmful volatile gas (ammonia nitrogen, 3-methyl indole, p-Cresol and DL-Lactamide, propyl ether) which is caused by the immediate supplementation with dried mulberry leaves. The present study revealed that added mulberry leaves could promote absorption of animal’s nutrients and immune health. Furthermore, the addition of mulberry leaves, especially fermented mulberry leaves, contributed to the optimization of the livestock environment and strengthen environmental protection. These findings provide valuable insights into the potential applications of mulberry leaves as forage in animal husbandry.</p>