A major objective in managing high yielding cows at grass is to maximise total DM intake. However, behavioural factors associated with grazing limit herbage intake, and concentrate supplementation is required to sustain yields. In a previous study (Pulido and Leaver, 1985), a level of 6 kg concentrates/day, at a high sward height (7 to 9 cm) failed to prevent high rates of milk yield decline (> 0.19 kg/day). An ad libitum level of concentrates was included in this study to examine the extreme end of the response curve.