Both the farm-specific and regional costs of clean feeding as a countermeasure to reduce ingestion of contaminated grass when there is insufficient supply of other types of roughage were estimated for dairy farming in Finland in the first year after contamination. The cost estimation considered expenditures and revenues associated with milk production and were calculated using farm models developed for economic planning. A hypothetical contamination scenario was designed using RODOS models for atmospheric dispersion and transfer in terrestrial food chains. Costs for intervention after two similar hypothetical atmospheric dispersion and deposition scenarios in early June and in July were estimated. As a reference, the cost of complete replacement of fodder throughout the area was also calculated. Feed substitution costs were higher in June than in July, due to the availability of some harvested silage in the later scenario. In the first case, the additional costs of clean feeding amounted to one-fifth of the normal production costs. Effective advisory/support services, available to farmers, can substantially improve the implementation of countermeasures. However, high costs and insufficient sources of clean feed would restrict the use of clean feeding as the sole countermeasure after serious contamination during the growing season.