This book contains a compilation of offered papers presented at the main congress of the XX International Grassland Congress held in University College Dublin, Ireland from 26 June to 1 July, 2005. It is complemented by six other books arising from the XX IGC as listed on the back cover: the book of invited papers from the main congress and five books containing the proceedings of five satellite workshops held immediately after the main congress at locations in the UK and Ireland (Aberystwyth, Belfast, Cork, Glasgow and Oxford). The workshops were designed to facilitate more in-depth presentations and discussions on more specialised topics of worldwide significance. The main congress brought together scientists from many disciplines, policy makers, consultants and producers involved directly in grass production and utilisation, as well as people in associated industries. They discussed issues around the theme of the congress, Grasslands: a Global Resource. The congress programme was organised around three main thematic areas: Efficient Production from Grassland, Grassland and the Environment, Delivering the Benefits from Grassland.