grazing

Anecdotal evidence from animal charities indicates that the number of overweight donkeys in the UK is increasing. Donkeys commonly have daily access to pasture therefore knowledge of grass intake is essential if feeding advice is to be relevant. The effects of herbage mass and length of grazing time on diet composition and dry matter intake (DMI) by mature donkeys were determined.

There were two measurement periods: period 1 during autumn when pasture was sparse (herbage mass 92 + 7g DM/m2) and period 2 during summer when pasture was more abundant (herbage mass 197 + 12g DM/m2). Twenty mature donkeys were selected and split into three grazing groups (8, 12 and 23 h daily grazing access). Barley straw was fed ad libitum and each donkey was given 150mg per day of an n-alkane marker Dotriacontane (C32) for the 12 d of each study period. Herbage mass significantly affected total DMI and diet composition. During summer DMI of donkeys in the 8 and 23h groups was significantly greater than during autumn (P<0.05). The proportion of grass in the diets of all donkeys was also greater in summer compared to autumn (P<0.001). Grazing time did not significantly influence total daily DMI during either season due to donkeys consuming more straw when grass intake was reduced. Restricting donkeys to 12h or less grazing per day in summer significantly (P<0.001) reduced their grass intake compared to that of donkeys with 23h access. When grazing sparse pastures (autumn) time allowed for grazing did not influence grass intake. The results show that time allowed for grazing per se was less important than the herbage mass available to the donkey in terms of grass DMI.

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.