Liquid feed has to be pumped through pipes to deliver it to pigs. The dry matter content of the diet and the distribution of particle size affects a number of physico-chemical properties of the process. These determine the initial power needed to start a pump from the stationary position and to circulate the feed through the system. Particle size also affects the homogeneity of the diet and the extent to which separation occurs during pumping and after delivery to the trough. In ad lib. feeding systems there is an opportunity for feed particles to hydrate and increase in size. These changes could have a significant effect on viscosity and hence the DM concentration of the diet that could be pumped at a particular power loading. In dry diets, particle size distribution is normally assessed and described on the basis of simple dry sieving. However, this method cannot be used with liquid diets. In other applications, the sizes of particles in a suspension have been assessed using laser particle size analysis (Chmelik et al. 2001). This study was designed to 1) Determine the extent to which particle size distribution was changed by different disk mill settings; 2) Examine the change in particle size distribution resulting from steeping the cereal component in water for 24h; 3) Determine the effect of particle size on viscosity.