In general cows have higher intakes and higher milk yields when outdoors grazing pasture compared to indoors consuming grass silage. However, this observation is not valid as a direct comparison of grass and silage due to the following reasons. Firstly, the cows consuming the silage and grass are usually at different stages of lactation and secondly the silage has not been produced from the herbage being grazed. There is little information available in the literature comparing the intakes of grass and silage harvested from the same sward at the same stage of maturity when fed to lactating dairy animals at similar stages of lactation. The present study was initiated as part of a series of studies at this Institute, to evaluate factors affecting silage intake. The main aims of this study were to determine the actual effect which ensiling “per se” had firstly on dry matter intake and secondly on animal performance by the lactating dairy cow.