In its common modern meaning, a mule is the offspring of a male donkey and a female horse. Compare hinny — the offspring of a male horse and a female donkey. more...
The term "mule" (Latin mulus) was formerly applied to the offspring of any two creatures of different species — in modern usage, a "hybrid".
The mule, easier to breed and usually larger in size than a hinny, has monopolised the attention of breeders. The chromosome match-up more often occurs when the jack (male donkey) is the sire and the mare (female horse) is the dam. It has been known for people to let a stallion (male horse) run with a jenny (female donkey) for as long as six years before getting her pregnant. Male mules and hinnies are both sterile, as are almost all female mules and hinnies (see External links). The sterility is attributed to the different number of chromosomes the two species have. Donkeys have 62 chromosomes, while horses have 64.
A female mule, called a "molly," has estrus cycles and can carry a fetus, as has occasionally happened naturally but also through embryo transfer. The difficulty is in getting the molly pregnant in the first place.
In its short thick head, long ears, thin limbs, small narrow hooves, short mane, absence of chestnuts (horny growths) inside the hocks, and tail hairless at the root, the mule appears asinine in form. In height and body, shape of neck and croup, uniformity of coat, and teeth, it appears equine. Also characteristic of the mule is its enormous phallus, hence the popular colloquial expression. It has the voice neither of the ass nor of the horse, but emits a feeble hoarse noise. Most mules have a brown or bay-brown coat — bay, or bright bay, or piebald occur rarely; a chestnut tint sometimes appears.
The mule possesses the sobriety, patience, endurance and sure-footedness of the ass, and the vigour, strength and courage of the horse. Operators of working animals generally find mules preferable to horses: mules show less impatience under the pressure of heavy weights, while their skin, harder and less sensitive than that of horses, renders them more capable of resisting sun and rain.
Humans have used mules from early times; the inhabitants of Mysia and Paphlagonia allegedly bred the first mules. The ancient Greeks and especially Romans valued mules for transport, employing them to draw carriages and carry loads. Mules hauled barges in the early days of the Erie Canal. In the early 20th century use of mules survived mainly in military transport, being used to haul caissons and artillery through nearly impassable terrain, the bravery and focused intelligence of the animal serving it well in the midst of the noise and confusion of warfare.
Mules have become far less common since the rise of the automobile, the motorized tractor, and other internal combustion-powered vehicles. They still find employment in less-developed countries, and in certain specialized roles for which they are still aptly suited. Mules can negotiate well on narrow, steep trails — such as the route from the South Rim down into the Grand Canyon. (The animal used for tourist transport on the Bright Angel Trail in the Grand Canyon is the burro, a variety of donkey.) Mules (and burros) can handle extremely rugged terrain and tracks that are too steep and twisted for either the less sure-footed horse or for a motor vehicle. Mules are also shown at equine shows.
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