To better understand rumen adaptation during dietary transitions between high- and low-quality forages, 10 rumen-cannulated Hu sheep were randomly allocated to two dietary treatments (five sheep each) with the same concentrate-to-forage ratio and concentration mixture, but different forage sequences: (i) alfalfa hay (AH) to corn stover (CS) and back to AH; and (ii) CS to AH and back to CS. A significant decrease in the rumen microbial protein concentration was observed on day 6 after dietary transition whether the transition was from AH to CS or from CS to AH, and this was accompanied by an increase in the ammonia nitrogen concentration as well as a decrease in the total volatile fatty acids concentration and pH. However, after transitioning back to the original forage, the rumen fermentation parameters returned to their initial levels within 2 weeks. Our findings suggest that abrupt substitutions of forages with large nutrient differences could influence rumen function to some extent, but recovery can occur within 2 weeks without detrimental effects. Furthermore, we speculate that the variation of fermentation in the first 6 days may indicate an important rumen transition stage that requires further study.