Donkeys, like mules, need less protein and more fiber than horses. Although the donkey's gastrointestinal tract has no marked differences in structure to that of the horse, donkeys are more efficient at digesting food and thrive on less forage than a similar sized pony. They only need to eat 1.5% of their body weight per day in dry matter. It is not fully understood why donkeys are such efficient digestors, but it is thought that they may have a different microbial population in the large intestine than do horses, or possibly an increased gut retention time.