The objectives of this study were to determine the effects of breed, season and pasture moisture gradient on the extent and location of grazing and ruminating behaviour in cattle kept on heterogeneous semi-natural grasslands. Two groups of heifers, 12 of the traditional Swedish breed Vtheneko and 12 of the commercial Continental breed Charolais, were allocated into three enclosures per breed. Each enclosure consisted of heterogeneous semi-natural grasslands dominated by Deschampsia cespitosa (tufted hairgrass) and each contained dry, mesic and wet areas. In spring, summer and autumn, behaviour was recorded using automatic behaviour recorders, and positioning and activity were recorded using GPS receivers for 24 h for every heifer. The Vtheneko heifers had a higher activity than the Charolais heifers (P = 0.006), which supports the theories of resource allocation and contrafreeloading, but there were no differences between breeds in location of grazing, ruminating or idling. The heifers spent more time grazing in autumn (42.5% of the day) than in spring (38.5%; P = 0.006) and summer (38.9%; P = 0.014) and the efficiency of grazing (i.e. proportion of eating during grazing bouts) increased over the grazing period (P <0.001). The results indicate the heifers avoided grazing in darkness which is consistent with the theory that predation risk affects foraging. Herbage in wet areas had a lower concentration of crude protein (P = 0.036) and a higher concentration of neutral detergent fibre (P = 0.011) than herbage in dry areas. At the same time, on average over seasons, 28% of the herbage mass was found in the wet areas, whereas only 8% of the grazing occurred there. Furthermore, the proportion of eating during grazing bouts was lower (73.9%; P <0.001) in wet areas than in dry (80.1%) and mesic (79.6%) areas. The results indicate the heifers avoided grazing in wet areas where forage had a low nutritional value, supporting the theory of optimal foraging. In conclusion, both breed and season affects foraging behaviour of cattle on semi-natural grasslands, as the heifers of the traditional breed had a higher activity than the commercial breed and the grazing time was longer and more effective in late than in early grazing period. The cattle avoided foraging in wet areas, which may impact on the management of these areas.