Grazed grass is often considered to be one of the cheapest feeds for dairy cows, the cost of grazed grass is largely determined by the yield of herbage produced and the efficiency of utilisation by the grazing animal. Recent farm surveys and an assessment of detailed costings suggest that alternative forages may be cheaper than grazed grass in some situations, particularly if herbage yields are low and utilisation is poor (Kilpatrick et al., 2002). The objective of this experiment was to examine the effect of altering the grazing interval, in a rotational grazing system, on grass growth and utilisation, and on animal performance.