It is common practice to give cereal fed bulls a 160g/kg crude protein (CP) diet to 250kg live weight, dropping to 140g/kg CP from 250kg to slaughter. The majority of intensively fed beef cattle are fed home mix rations based on rolled barley with a protein concentrate or ‘protein rich’ straights such as rapeseed meal and soya bean meal. In this latter situation higher protein rations will have increased ration costs. The objective of this experiment was therefore to determine the effect of feeding barley based rations containing 120, 140 or 160g/kg dietary CP on the performance of cereal fed 280kg Holstein bulls through to slaughter.