Reduction of grazing intensity is assumed to favour biodiversity as a result of increased pasture heterogeneity, but there is a clear lack of data on the impact of grazing horses at different stocking rates. Over a 4-year study, we therefore recorded the species richness and abundance of vascular plants (25 fixed 50 cm × 50 cm quadrats per plot), ground beetles (18 pitfall traps per plot) and grasshoppers (three fixed 50 m long transects per plot) in a mesophile grassland that was continuously grazed by horses at either 1.8 or 1.1 LU ha-1. Average number of plant species per plot (n = 28) was not affected by stocking rate, but the creation of relatively stable short patches by horses enabled legumes to compete with tall grasses. Consequently, legume abundance increased from an average of 0.042 to 0.157 of plot area at the high stocking rate, while remaining stable around 0.082 in moderately grazed plots (SR×year: P = 0.024). Higher structural heterogeneity in these last plots led to favour groundbeetle and grasshopper populations, especially those species asso