for: U.S. Military M274 Truck, Platform, Utility 1/2 Ton, 4X4

In its common modern meaning, a mule is the offspring of a male donkey and a female horse, which is classified as a kind of F1 hybrid. The much rarer offspring of a male horse and a female donkey is called a hinny. The term "mule" (Latin mulus) was formerly applied to the infertile offspring of any two creatures of different species. The mule, easier to breedFact: date=September 2007 and usually larger in size than a hinny, has monopolized the attention of breedersFact: date=September 2007. The chromosome match-up more often occurs when the jack (male donkey) is the sire and the mare (female horse) is the dam. Sometimes people let a stallion (male horse) run with a jenny (female donkey) for as long as six years before she becomes pregnant. Mules and hinnies are almost always sterile (see fertile mules below for rare cases). The sterility is attributed to the differing number of chromosomes of the two species: donkeys have 62 chromosomes, whereas horses have 64.

A female mule that has estrus cycles and can carry a fetus is called a "molly" and can occasionally occur naturally as well as through embryo transfer.

Size

The median weight range for a mule is between 800 pounds to 1000 pounds.

Characteristics

A mule does not sound exactly like a donkey or a horse. Instead, a mule makes a sound that is similar to a donkey's but also has the whinnying characteristics of a horse (often starts with a whinny, ends in a hee-haw). Sometimes, mules whimper. The coats of mules come in the same varieties as those of horses. Common colors are Sorrel, Bay, Black, and Grey. Less common are White, Roans (both blue and red), Palomino, Dun, and Buckskin. Least common are Paint mules or Tobianos.

The mule possesses the sobriety, patience, endurance and sure-footedness of the donkey, 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, and their skin, harder and less sensitive than that of horses, renders them more capable of resisting sun and rain. Their hooves are harder than horses', and they show a natural resistance to disease and insects. Many North American farmers with clay soil found mules superior as plow animals, especially in the U.S. state of Missouri, hence the expression "stubborn as a Missouri mule".

Mules are generally less tolerant towards dogs than horses are.Fact: date=September 2008 They are also capable of striking out with any of their hooves in any direction, even sideways if needed.Fact: date=September 2008

Mules exhibit a higher cognitive intelligence than their parent species - horses and donkeys. This is believed to be the result of hybrid vigour, similar to how mules acquire greater height and endurance than either parents.