Compared with most grass silages, maize silage has a low ratio of rumen degradable protein: fermentable energy. Unlike grass silage, maize silage contains rumen fermentable starch. These differences imply that a different regimen of supplemental nutrients is required to optimise cow performance on rations containing maize silage compared with rations based on grass silage. The objective of this study was to define responses of dairy cows fed rations based on maize silage to supplements of rumen fermentable starch (RFS) and effective rumen degradable protein (ERDP).