To assess the effect of grassland management on the ruminal digestion of silages, four lactating dairy cows, fitted with a rumen cannula, were fed diets consisting of concentrates and different grass silages. The grass silages consisted of intensively managed grass (IM) in variable proportions replaced by silages harvested from a ‘species-poor’ grassland managed to stimulate nesting of birds (SPP) or from a grassland managed to increase plant species diversity (SPR). The roughage part of the diets was composed completely of IM (100IM), or 200 g/kg (in dry matter) of IM replaced by SPP (20SPP) or 600 g/kg of IM replaced by SPP (60SPP), or SPR (60SPR). The pH in the rumen was highest on 60SPR and lowest on 100IM and 20SPP (P<0·05), whereas volatile fatty acids (VFA) concentrations were lowest on 60SPP and 60SPR and highest on 100IM (P<0·05). No differences in the ratio non-glucogenic: glucogenic volatile fatty acids were observed among the diets. The NH3 concentration was highest on 100IM and 20SPP and lowest on 60SPR (P<0·05), reflecting differences in CP intake. The concentration of uric acid in the urine (mg per kg metabolic body weight) was highest on 100IM (P<0·05). Rumen pool size of OM and DM did not differ among treatments, but pool size of NDF and IADF were highest on 60SPR (P<0·05). Passage rate was high on 100IM and 60SPR, but no significant differences with the other treatments were established. Also, no significant differences were observed in rates of degradation. Clearance rate of large particles was highest on 60SPP and differed significantly from 60SPR (P<0·05) only. No differences were observed in clearance rate of small particles. In conclusion, for most rumen fermentation characteristics measured in the study, no noticeably aberrant behaviour of the silages from semi-natural grassland was observed.