An in situ study was conducted to determine the effect of feeding red osier dogwood (ROD) on ruminal digestion of barley, ROD, and barley silage in beef heifers. Heifers were fed diets that varied by substituting ROD for barley silage at 0%, 3%, 7%, or 10%. Slowly degradable fraction and effective degradability (ED) of ROD crude protein (CP) linearly (P < 0.02) increased with increasing ROD. The ED of CP of barley and barley silage was reduced (P < 0.01) by feeding ROD. These results indicate that feeding ROD potentially reduces ruminal protein degradability, thereby improving protein efficiency.