Benefits when yeast cultures are added to ruminant diets may include increased intake, ruminal fibre digestion, reduced ruminal accumulation of lactic acid, increased growth efficiency in beef cattle and increased milk yield in dairy cows. However, the effects on milk performance can be variable, with small or negative responses being reported, as well as positive effects. Part of this variation may be attributable to differences in animal potential and basal diet, and it has been suggested that the greatest benefit may occur in high yielding cows when fed diets high in high starch. The objective of the current experiment was to determine the effect of a yeast culture on the intake and performance of high yielding dairy cows fed a complete diet that was high in starch.