The limited availability of food, together with the constraints that traditional management systems impose on the natural foraging behaviour of donkeys, often results in severe under-nutrition. Few studies have been conducted into the digestibility of different forages and little information exists on nutritional requirements of donkeys. In order to measure digestible energy requirements of donkeys under tropical conditions, an experiment was carried out at the Centre for Research in Agricultural Science (CICA) and the Faculty of Veterinary Medicine of the Universidad Autónoma del Estado de México located in the Toluca valley, Central México. Thirty-two donkeys of a body condition typical for Central México were divided into four groups of 8 animals each according to their sex and live weight: group 1 (Gl) comprised male donkeys below the average body weight (102 ± 5 kg); group 2 (G2) comprised male donkeys of average body weight (121.5 ± 4 kg); group 3 (G3) comprised female donkeys below average weight (111.8 ± 5 kg); and group 4 (G4) comprised female donkeys of average weight (127.6 ± 5 kg). A diet of oat straw or maize stover and 15% alfalfa hay was offered to meet exact maintenance requirements. The donkeys were monitored for 13 months. The live weight of all animals was recorded daily in order to monitor whether maintenance requirements were being met. Mean daily digestible energy (DE) requirements were measured during the winter, spring, summer and autumn of 2003–2004. Digestible energy requirements of all four sex and liveweight groups were significantly (p > 0.05) higher during the spring than during the other seasons of the year (13.5, 18.0, 10.4 and 14.3 MJ DE per day during winter, spring, summer and autumn, respectively). Predicted DE requirements of donkeys with a live weight range betweenn 90 and 150 kg using the data from the present study were less than those predicted using scaled-down horse feeding standards.