In their native arid and semi-arid climates, donkeys spend more than half of each day foraging and feeding, often on poor quality scrub. The donkey has a tough digestive system in which roughage is efficiently broken down by hind gut fermentation, microbial action in the caecum and large intestine. While there is no marked structural difference between the gastro-intestinal tract of a donkey and that of a horse, the digestion of the donkey is more efficient. It needs less food than a horse or pony of comparable height and weight, approximately 1.5 percent of body weight per day in dry matter, compared to the 2–2.5 percent consumption rate possible for a horse. Donkeys are also less prone to colic. The reasons for this difference are not fully understood; the donkey may have different intestinal flora to the horse, or a longer gut retention time.