A shortage of high quality forage may force smallholder farmers to suddenly change their cow ration to variable forages available locally such as cereal stover. To understand the adaptation and recovery of rumen is of importance for minimizing the adverse effect during transition of different quality forage. In a 3-periods crossover study, 10 ruminal cannulated sheep (BW = 15.1 ± 0.5 kg) were equally allocated to 2 treatments with same concentration mixture but different forage sequences: (1) alfalfa hay (AH) to corn stover (CS) then back to AH; and (2) CS to AH then back to CS, in quick succession for 21 d. Each forage treatment lasted for 2 wk and rumen contents were collected before morning feeding on d 0, 1, 2, 4, 6, 9 and 14, respectively after first and second transition. Rumen content samples were also collected 3 and 6 h after morning feeding during transition for short-term observation. The ruminal pH, ammonia nitrogen, volatile fatty acids and microbial protein (based on purine method) were analyzed. The data were analyzed according to mixed linear model and visualized using R with ggplot2 packages. The pH value did not change with the transition (P > 0.05). Rumen fermentation variables reversed on d 1 of forage transition between 2 sequences. Microbial protein concentration was decreased (P < 0.01) from 6.78 on d 1 to 5.21 mg/dL on d 6 with transition from AH to CS, and from 7.86 on d 1 to 5.97 mg/dL on d 6 with transition from CS to AH in either sequence, along with corresponding increase in ammonia nitrogen (P ≤ 0.01). Total volatile fatty acids did not change with transition from AH to CS, but decreased with transition from CS to AH. Nonetheless, after transition back to original forage in the third period, rumen fermentation variable returned to initial levels with no difference from those on d 0. Our finding suggested that abrupt forage substitution with large nutrients difference could influence rumen function during the immediate transition to some extents, but it can eventually recover within 2 wk without detrimental effects. The first 6 d after forage transition when the rumen fermentation was critically disrupted are the key times that need further concern.