The effect of digestibility and forage species on the removal of digesta from the rumen and the voluntary intake of hay by sheep.

1. The characteristics of digestion, passage and rumen fill of three hays: early- and late-cut perennial ryegrass (Lolium perenne cv. Endura) and white clover hay (Trifolium repens cv. Blanca and Pronitro) were studied using six rumen-cannulated sheep fed at a restricted level of intake (18 g dry matter (DM)/kg live weight (LW) per d), in a two 3 x 3 Latin square design. 2. Voluntary intake of the same diets was measured using a further six non-cannulated sheep in a similar design. 3. Rate of digestion of the three hays was measured using dacron bags and the rates of digestion of DM and neutral-detergent fibre (NDF) for clover hay were significantly (P less than 0.05 and P less than 0.001 respectively) faster than those for the two grass hays whose rates did not differ. Rates of passage, determined using chromium-mordanted hay, did not differ between treatments. 4. Rumen pool sizes of DM, organic matter and fibre were generally greatest for the late-cut grass hay and lowest for the clover hay, while voluntary intake was highest (P less than 0.001) for the clover hay (36.6 g DM/kg LW per d) and lowest for the late-cut grass hay (24.7 g/kg LW per d). 5. The net rate of removal of indigestible fibre from the rumen appeared to vary within the day, with maximal disappearance occurring during eating, followed by a lag phase between 5 and 10 h after feeding, with a second increase in rate between 10 and 24 h post-feeding.