In a previous experiment (Hovell et al. (1987)) it was found that with two roughages, one of good (hay) and the other of poor (straw) degradability, both ground and pelleted, that the voluntary intake of the hay was (60% greater than that of the straw. This was despite the fact that rumen DM pool sizes were very similar. The outflow of undegraded material from the rumen was much greater with the hay although particle size should not have been a constraint to outflow with either roughage (Poppi et al. (1980)), and indeed their particle size distributions were very similar. It was suggested that there might have been an effect of roughage quality on rumen outflow rate, possibly mediated through an effect on reticulo-rumen contractions.
The objective of the experiment reported here was to examine the effect of roughages with different degradabilities on voluntary intake, rumen volume, rumen outflow rate, and on reticulo-ruminal contractions.