Animal performance from grassland is dependant both on the grass growth achieved and the efficiency of utilisation. The Grassland Research Institute and ADAS conducted a series of trials (GM 20) which showed grass growth to be mainly influenced by the available water capacity of the soil, summer rainfall and altitude. This gives a site class which together with the fertilizer used determines the quantity of herbage grown.Less is known of the variation in utilisation of the grass grown. This analysis has been undertaken to assess the levels of grassland utilisation found on dairy farms of England and Wales.