There is an increasing trend in agriculture to use biochar (BC) as a means for carbon storage and soil improvement, and it has been suggested, that feeding BC to livestock can improve animal health and performance, and reduce enteric methane emissions. The aim of this study was to investigate if adding BC to a balanced ration of a group of lactating Holstein dairy cows had an effect on their milk yield and quality, methane emission, nutrient digestibility and health. In a crossover experiment lasting for two 36-day periods, eight cows received their basal ration with and without 1 % DM BC. During the last week of each period, the cows were kept in tie stalls where milk yield and composition, feed intake and nutrient digestibility, as well as blood parameters were quantified. On the last two days, methane emissions were measured in respiration chambers. The results indicate that there was no significant effect of the addition of BC on any of the measured variables. Voluntary intake was not affected by the addition of BC (P=0.52) and none of the cows exhibited health problems in response to the treatment. There was no increase in milk yield (P>0.46) or composition (P>0.23) and methane emissions were not significantly affected (P>0.37). While the beneficial effects of feeding BC to animals suffering from health problems or receiving a poor diet cannot be excluded, the data of this experiment indicate that BC is not an effective feed additive to improve performance or reduce methane emission in dairy cows.