Measuring daily food intake of foraging animals is essential if accurate feeding rations are to be implemented. The alkane technique, which has recently been validated in equines, now provides the opportunity to measure intake at pasture. The aims of this study were to determine the effects of herbage mass and grazing time allowance on dry matter intakes in mature donkeys in the UK. The effect of grazing time allowance on diet composition was also measured. Two study periods took place; period 1 when pasture was sparse (herbage mass 133.1±10 g dry matter/m2) and period 2 when pasture was more abundant (herbage mass 284.5±17.2 g dry matter/m2). Eighteen mature donkeys, male and female, were selected for the study and split into three grazing groups. Groups 1 and 2 were restricted to 8 and 12 hours grazing time per day, respectively. Group 3 was allowed 23 hours grazing time daily. Access to a yarded area and shelter was available to all donkeys during grazing periods. Barley straw was fed ad libitum to all donkeys and was available at all times. Each donkey was administered with 150 mg per day of an n-alkane marker Dotriacontane (C32) in the form of a labelled wheat biscuit fed three times daily for the 12 days of each study period. During period 1 grazing time allowance had no significant effect on daily DMI although the donkeys with 23 hours access did consume more than donkeys with only 12 and 8 hours grazing access (2.61, 2.54 and 2.26 kg, respectively). The proportion of grass and straw comprising daily intake was affected by grazing time allowance (P<0.05). Grass comprised 18% of daily intake for the 8 and 12-hour groups and 11% in the diet of the 23-hour group, although this difference was not significant. During period 2 daily DMI remained unaffected by grazing time allowance. The proportions of grass and straw within the diet were significantly affected (P<0.001), grass comprised 25 and 29% of daily intake for the 8 and 12-hour groups but made up 41% of daily intake of the 23-hour group. These results show that grazing time allowance has little effect on overall DMI but when given the opportunity donkeys increase their grass intake.