The objective of the present study was to compare the effect of whole crop faba bean silage with grass silage as forages for lactating dairy cows. The experiment also allowed comparison of the milk production response of faba bean crude protein (CP) to that derived from a rapeseed meal supplement. Three experimental diets were used: (1) Grass silage supplemented with a cereal-based concentrate (CON), (2) 75% of grass silage replaced on dry matter (DM) basis with whole crop faba bean silage supplemented with a cereal-based concentrate (FB) and (3) Grass silage supplemented with a cereal and rapeseed meal-based concentrate (RSM) so that it was isonitrogenous with FB. The diets were fed as total mixed rations and the target proportion of concentrate in total diet DM was 400 g/kg. The experimental design was a nine times replicated 3 × 3 Latin square and 27 dairy cows were recruited into the experiment. Diet DM intake was significantly greater (P < 0.05) with FB and RSM compared with CON, which was reflected in lower (P < 0.05) milk, energy corrected milk and milk protein outputs of cows on CON than those on FB and RSM. There were no significant differences in milk and protein yields between FB and RSM but energy corrected milk and milk fat yields were greater on RSM (P < 0.05). Milk urea content was lowest in CON and highest on FB while RSM was intermediate (P < 0.05). Whole crop faba bean silage provides a viable option for feed production of dairy farms under Northern European climatic conditions with positive influence on e.g., biodiversity and flexibility in harvesting schedules. In spite of the moderate energy value of faba bean silage, it has a good feed intake potential, and when replacing grass silage in the diet, can be assumed to maintain or even increase milk yield. The higher supply of CP from FB compared to that of grass silage is however not as valuable as that originating from rapeseed meal, and decreasing nitrogen use efficiency seems inevitable irrespective of the source of additional CP content in the diet of dairy cows. All rights reserved, Elsevier.