Rapid breakdown of herbage proteins in the rumen and inefficient capture of nitrogen (N) by the rumen microbial populations are a major source of N loss and pollution in pasture-based ruminant agriculture. Degree of cell damage during mastication and ingestion varies between grass species with consequences for release of cell contents (protein, sugars and lipids) into the rumen (Kim et al., 2008). Consequently, grazing cattle on different grass species may provide an opportunity to manipulate N efficiency. The purpose of this study was to compare N utilisation efficiency by dairy cattle grazing grass species differing in chemical and morphological characteristics.