Microscopical analysis of epidermal fragments in stomach contents or faeces is in a helpful tool in assessing the diet of herbivores. Two aspects can cause differences between stomach and faecal samples and should be taken into account establishing correction factors for diet composition: (1) differential digestion or retention of different plant species or plant parts; and (2) differences between meals (short-term changes in diet). In the present study faeces mean/stomach mean presence of a plant species is interpreted as a measure of digestibility and used as conversion factor for differential digestion of that species.