In the Southern Hemisphere, ruminants are mostly raised in grazing systems where animalsconsume forage and are supplemented with low amounts of concentrates. Concentratesare usually given separately and are rapidly ingested. This practice leads to changingrumen environment conditions during the day, may alter the rumen microbial metabolismand could affect host performance. The native ruminal Prevotella bryantii strain 3C5 wasadministered every 48 h to wethers under experimental conditions simulating Southern-Hemisphere feeding to evaluate its potential as a rumen fermentation modulator. Theinoculum potential was assessed on day 17. The ammonia nitrogen (NH3-N), volatile fattyacids and ruminal pH were monitored on a 24-h basis 19 days after the beginning ofthe experiment, and the microbial community structure was assessed by pyrosequencing.The administration of P. bryantii modified the fermentation products and daily pH valuescompared to the control. The NH3-N concentration in the rumen of treated animals wassignificantly higher than that of the untreated animals. Modification of the ruminal envi-ronment and fermentation pathways was achieved without altering the general structureof the microbial community or the potential methane production. P. bryantii 3C5 could beconsidered in potential probiotic formulations for ruminants in semi-intensive systems.