Grain processing and particle size is one of the biggest factors affecting how efficient pigs are in utilising the grains within their diet. This project evaluated the particle size distributions of milled grains currently used in feeds by both large and small producers. Trials were completed to test whether variations in particle size below one millimetre for field peas and sorghum influenced feed conversion growth rates in weaner pigs. The research also investigated the composition and particle size of leftover feed in the small intestine to determine passage time in the gut.