The mean retention time (MRT) of stained hay through the whole digestive tract and feed digestibility were measured in Japanese sika deer (Cervus nippon) and were compared with those in sheep in summer (July) and winter (February) when lucerne (Medicago sativa) hay was fed at 2% of body weight. MRT for both species in winter was significantly shortened, while digestibility was significantly reduced, compared with in summer. Furthermore, the values of MRT and digestibility for deer were always smaller than those for sheep in both seasons. From these results we concluded that there are seasonal changes and differences according to species in the food digestibility of sika deer and sheep, and that the difference and/or alteration in controlling the passage of feed particles through the whole digestive tract might be responsible for these changes.
