The effects of an increase of rumen fill obtained with polystyrene cubes, and able to stimulate mechanically the rumen wall were investigated on alimentary behaviour and reticulo-rumen motility in sheep. The introduction through a rumen cannula of a volume of polystyrene cubes equal to one-quarter of the ruminal pool size depressed the daily intake of both low-quality cocksfoot hay and good-quality lucerne hay (P < 0·05). Surprisingly, the time spent ruminating was slightly increased and the frequency of contractions during rumination was significantly increased (P < 0·05). In addition, in the sheep fed enterally with a liquid into the rumen, either the mechanical stimulation of the rumen dorsal wall or the introduction of hay (200 g) into the rumen, induced a rumination molility pattern. It is concluded that the intensity of mechanical stimulation of the dorsal sac of the rumen by food particles, which depends upon rumen fill, reduces the time spent eating to increase the duration and intensity of rumination.
