Mules are an equid hybrid produced by crossing a female horse and a male donkey. Enthusiasts claim mules combine the best of both species, offering the strength, endurance, and patience of the donkey with the speed, agility, and aesthetics of the horse.

Mules are often praised for their hardiness, intelligence, and lesser need for maintenance compared to horses, making them a popular choice for a variety of tasks, from farm work to trail riding. These equids are still used as working animals around the world.

While mules share traits with horses and donkeys, they also have unique characteristics. Although there is limited research available on the welfare and management of mules, new studies have found significant differences between these hybrids and horses.

With their growing popularity as recreational mounts and pets in North America, it is important for owners and handlers to understand these differences. This profile will discuss the history, characteristics, health problems and nutritional needs of mules. Keep reading to learn more about feeding and caring for these equids.

What is a Mule?

A mule is a hybrid animal resulting from the crossbreeding of two different species within the Equidae family: a male donkey and a female horse. This crossbreeding results in offspring with a blend of traits from both parents.

Mules typically exhibit physical and behavioral characteristics inherited from both donkeys and horses. They often have the body shape and size of a horse, with long, strong limbs and a muscular build, but also inherit the donkey’s hardier, more resilient nature.

Mules have longer ears than horses, a trait characteristic of donkeys, and their coats, tail, and mane may also resemble that of a donkey. They are also less prone to many of the genetic diseases that horses are susceptible to and often have a longer lifespan.

Equids and Hybrids

The term “equid” can refer to any animal that belongs to the Equidae family. Equus is the only surviving genus in this small taxonomic family. This genus consists of three subgenuses. [6]

  • Horses: Includes the domesticated horse (Equus caballus) and the Przewalski’s horse (Equus ferus przewalskii).
  • Asses: Includes the African wild ass and domesticated donkey (Equus africanus), the Asiatic wild ass (Equus hemionus), and the Tibetan wild ass (Equus kiang).
  • Zebras: Includes the Plains zebra (Equus quagga), the Grevy’s zebra (Equus grevyi), and the Mountain zebra (Equus zebra).

Crossbreeding different species in the Equidae family produces equid hybrids. Most hybrids are sterile and cannot produce offspring.

Types of Equid Hybrids

Hybrid names describe the species and sex of the parents.

  • Mule: Male horse and female donkey parents
  • Hinny: Male donkey and female horse parents
  • Zorse: Typically male zebra and female horse
  • Zonkey: Typically male zebra and female donkey

Can Mules Reproduce?

Mules are sterile and cannot reproduce due to chromosomal differences between horses and donkeys.

Horses have 64 chromosomes in their genetic material, while donkeys have 62. When a horse and a donkey mate, their mule offspring will have an intermediate chromosome count of 63 chromosomes, which generally leads to sterility.

This odd number of chromosomes disrupts meiosis, the process of cell division that produces reproductive cells, such as sperm or eggs. During meiosis, chromosomes pair up and then separate into new cells to ensure that each reproductive cell gets a complete set of chromosomes.

However, the uneven number of chromosomes in mules leads to cells that do not have the proper number of chromosomes. As a result, most mules end up with reproductive cells that are not viable, rendering them infertile.

Mule History

Humans have bred domesticated mules as beasts of burden for thousands of years. Crossbreeding donkeys and horses remained popular throughout history thanks to the mule’s practical talents.


Mules are the oldest known and most common equid hybrid. The mule name specifically refers to the offspring of a male donkey (Equus asinus) and a female horse (Equus caballus). A hinny is a less common hybrid produced by crossing a male horse and a female donkey.

Research suggests domestic horses originated in the Eurasian steppes, while domestic donkeys originated in East Africa. Genomic studies revealed humans domesticated donkeys approximately 3,000 years before horses. [1]

Other genomic studies identified mules dating from the Iron Age, which spans approximately from 1200 BC to 600 AD. These hybrids are also portrayed in ancient Egyptian iconography, suggesting Egyptians bred mules before 1000 BC. [2]

Historic Use

Mules are typically sterile and not suitable for breeding. As a result, these equids are only used for work. In several ancient civilizations, mules gained a reputation as robust, low-maintenance working animals. Egyptian iconography depicted mules pulling chariots and plows. [1]

For centuries, militaries used mules as pack animals. Archeologists identified remains of mules at Roman military forts dating as far back as 160 AD. [3]

Settlers in the Americas also used sure-footed mules to carry supplies over mountainous terrain and pull heavy loads in large teams. The American mining industry famously used 20 mule teams to pull wagon loads of borax out of Death Valley, California. [4]

While mule populations declined in industrialized countries in the twentieth century, some communities still rely on mules for their livelihood. Over 12 million mules live in developing countries, where they are still primarily used as working animals. [5]

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