AbstractUtilized Metabolizable Energy output was calculated and herbage utilization evaluated in two contrasting years on five profitable farms representing a range of soil types.Annual UME output was 72 GJ ha‐1on average, with a range from 47 to 91 GJ ha‐1. Grazed grass provided 66% of the utilized metabolizable energy, and conserved grass 34%. Higher utilized metabolizable energy output was not always obtained at higher fertilizer N inputs, even when soil moisture conditions favoured herbage growth.The efficiency of utilization of herbage conserved (almost always as silage rather than hay) was calculated by expressing utilized metabolizable energy output as a proportion of the quantity of herbage cut, measured by swath weighings; the mean value was 64%, with a range from 55 to 73%. Cellulose analyses indicated that mean dry matter losses via CO2and effluent were 10%; the remaining 26% loss appeared to be due to physical losses in the field, surface waste and wastage at feedout.For grazed herbage the utilized metabolizable energy output was expressed as a proportion of herbage accumulation measured over 28‐day periods. The resultant apparent efficiency of utilization averaged 67%, with a wide range from 51 to 83%. The lowest values were on badly drained farms.It is suggested that:(i) there is considerable potential for increasing output from grazing on dairy farms; higher grazing pressure and more flexible management would be needed. Targets should probably be set lower on badly drained soils;(ii) there is great potential for increasing the efficiency of utilization of conserved forage, by careful application of existing technology;(iii) on the farms studied the utilized metabolizable energy output from grazed and conserved fields appeared to be si