The literature suggests that supplementation of fibrous roughages with small amounts of rapidly fermentable carbohydrates can increase intake. A wide range of supplements has been used such as sugar beet pulp, (Silva, 1985), barley (Chimwano et al, 1976), maize starch (Huque, 1991) or sucrose (Campling et al, 1962). It has been suggested that one of the positive effects of rapidly fermentable carbohydrates on poor quality roughages is to provide extra fermentable organic matter, thereby enhancing microbial activity and fermentation of the less readily degradable components of the roughage. Thus Chappel and Fontenot (1968) used an 8 per cent concentrate inclusion with a roughage-based diet, and observed higher cellulose digestibility than without supplementation. We have suggested (Hovell et al 1988) that the outflow from the rumen of undegraded roughage residues is driven by salivary flow, rumen VFA levels stimulating saliva production during rumination. In this case, at least part of the effect of starchy concentrates on stimulating intake would be through a stimulation of rumen outflow. This hypothesis would seem to have been confirmed by the observations of Huque (1991) who supplemented a basal straw diet with maize starch (10, 20 or 30%) and observed an increased intake and rumen outflow with the lower levels of supplementation.

The objective of the experiment described here was to study the effect of the addition of starch to a straw diet on voluntary intake and rumen parameters including the dynamics of water flux.