Mule

Quick Take

• Mules outpaced horses on the American frontier by a staggering margin, and the real reason why reveals something unexpected about hybrid biology. See the hybrid advantage →
• Mules were supposed to be infertile by nature, yet documented exceptions exist that challenge everything we assume about hybrid genetics. Explore the chromosome oddity →
• George Washington had a secret weapon at Mount Vernon that shaped American agriculture, though it was not a crop. Washington's breeding program →
• The mule's legendary stubbornness is actually a myth, and its true temperament is the result of a very deliberate ancient engineering decision. Discover the real temperament →

What is a mule? Mules are a genetic hybrid that has been the workhorse of human civilization for millennia. Stronger than a horse, but gentler than a donkey, the mule combines all the best elements of both breeds into a package that is a staple of agricultural pursuits across the globe.

Incredible Mule Facts

• What is a mule? A mule is the offspring of a male donkey and a female horse.
• Mules are animals that were intentionally created during ancient times in order to highlight the best traits of the stallion and the donkey.
• Because mules have 63 chromosomes — 32 from the horse and 31 from the donkey — most are infertile.
• One of the earliest recorded instances of mules is in Ancient Egypt circa 3,000 BCE.
• They compete in all of the same equestrian events, including dressage, like horses.

Evolution

Mules have a long and storied history and have played important roles in civilizations all over the world. Horses originated in Central Asia around 3,500 BC and extended their range across the world, eventually overlapping with the range of the donkey, which originated in Africa. It is known that mules were bred in Mesopotamia before 1,000 BC. There is evidence in art and ancient writings that equids were present at many important events — for example, horses and Persian onagers are depicted in a painting in the Tomb of Nebamun at Thebes, dating from around 1,350 BC. Mules were present in Israel in the time of King David and were mentioned by Homer in the Iliad in 800 BC. George Washington bred mules at Mount Vernon. Mules pulled wagon trains across the American plains and could travel 30 miles a day compared to a horse’s five. The mule is famous the world over for its great strength and gentle manner.

Classification and Scientific Name

These animals are members of the family Equidae of the genus Equus. Their scientific name is Equus mulus, and that stands true for both the male and female of the species despite their different names. The mule is a hybrid of a male donkey, called a jack, and a female horse, called a mare. Equus is the Latin word for horse, and mulus is Latin for a mule.

Appearance and Behavior

Mules look exactly like what they truly are: the resulting genetic hybrid of a stallion and a donkey. While generally brown or gray, they can come in any coat and color found on both horses and donkeys. They are larger and leaner than donkeys (jacks) and smaller but stouter than horses (colts). Their heads are shorter, thicker, and more closely resemble those of donkeys, while their ears are longer than a horse’s but shorter than a donkey’s.

The average size of these animals is between 50 and 70 inches in height, and their weight can range between 600 and 1,500 pounds. Miniature animals weighing only 50 pounds have been bred, and the largest recorded male weighed in at a massive 2,200 pounds. That weight ranges from an average-sized male bulldog up to the weight of two grizzly bears put together. Apollo, the largest and heaviest mule, also stood an impressive 19 hands high, about 77 inches!

The mule’s temperament was the ideal that breeders sought when combining the qualities of horses and donkeys. In them, you find the strength and hardiness of a donkey combined with the temperaments of both parents. Stallions have a tendency to be flighty, or easily spooked, and jacks are known as stubborn and difficult to manage. The mule is a stolid, patient, and generally even-tempered beast.

Habitat

Mules are found throughout the world. They are located on every continent but Antarctica, and their breeding has left them well-suited to handle almost all climates. With their tougher skin compared to a horse’s, they are less likely to overheat, and they need less food than a horse, making foraging easier.

Mules are a human-created species and, as such, they have no natural habitat. They can be found anywhere that humans have brought them.

Diet

With respect to their diet, mules are no different from their parents. They eat a wide variety of grasses and small shrubs. If they do not have a large enough area to forage successfully, generally one to two acres, then their diet may be supplemented by hay, grain, or pelletized food.

Another result of the hybridization of the species is that, although they are the size of a horse, they require only a fraction of the food needed to feed a horse. When not working, they spend the majority of their day eating or resting.

Predators and Threats

The principal threat mules face is disease. Stallions, donkeys, and mules all face similar diseases such as tetanus, Eastern equine encephalomyelitis, and equine influenza. Appropriate care for the mule, frequent veterinary checkups, and vaccination programs all help to prevent these illnesses, or at least mitigate their effects. As wholly domestic animals, they do not typically face threats from predators.

Reproduction, Babies, and Lifespan

Mules are bred by crossing a mare with a jack. The mare gives birth to a baby, called a foal, after a gestational period of approximately 11 to 12 months. The average mule lives 35 to 40 years, though some have lived well into their 40s and beyond. Because mules have an odd number of chromosomes (63), they are often infertile. However, there have been instances of female mules giving birth.

Population

These animals exist on six of the seven continents, with Antarctica being the exception. They live almost exclusively in human care as, due to the fertility issues discussed above, they are largely unable to breed and sustain a feral population. Reliable population numbers are nearly impossible to come by; however, the U.S. Department of Agriculture reported approximately 200,000 mules residing within the United States alone as of 1998.

In the Zoo

These animals are common sights in zoos all across the United States. They are frequently found in petting zoos as well because of their even temperament. The San Diego Zoo has several mules, and the zoo recently donated several mules to CAL FIRE for use as pack animals in remote wilderness areas to assist in combating wildfires.