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Last updated date: 19th Apr 2024
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What is a Mule?

A mule is a draft and pack animal which is used in several parts of the world due to its ability to work and perform efficiently under strenuous conditions. It is a cross between a male jackass or ass and a female horse or mare. Conversely, pairing a male horse and female jackass gives us an offspring called the hinny or hinney, which is smaller in size as compared to the mule. Mules have been around for several thousand years, and we have records from over 3000 years ago stating the importance of mules as beasts of burden in Asia Minor. Mules are exceptionally hardy and can withstand hardships and severe working conditions. These animals are usually sterile. In this article, we will have a detailed discussion on the mule horse and discover some interesting facts about them. We will discover its similarities and differences to horses and donkeys, their characteristics and abilities, their fertility, history, where they are used, etc. 

Physical and Cognitive Characteristics 

In terms of height, the texture of the coat, the shape of its neck and croup, the mule closely resembles a horse. However, there are distinct differences when it comes to its long ears, short and thick head, short mane, slim legs, and small hooves. All these features belong to the family of the jackass. The colour of the coat in a mule animal is generally brown or bay. Mules can vary in height from 50 to around 70 inches. Their weight can be anywhere between 275 to 700 kg. The weight of the animal depends largely on the breeding of the mare, that is, the mule's mother. If she is a draft horse mare, the mule is more likely to be heavyweight. 

The mule is an example of an animal that is superior in characteristics to either of its parents, despite being a hybrid. Charles Darwin observed that the mule possesses greater intelligence, memory, sociable nature, muscle power, and life span as compared to both the horse and the jackass. He also stated that this is a curious happening. 

Traits that a mule inherits from its father are those of intelligence, cautious attitude, endurance capacity, sure-footed nature, etc. From the side of the mare, a mule inherits speed, grace, and agility. As observed by Darwin, mules are known to display greater cognitive abilities when compared to their parents. While mules stand at a greater height than donkeys, their endurance overtakes that of horses. 

Herders and animal handlers generally prefer mules to horses when it comes to heavy-duty. Mules are acclaimed for showing greater patience under strenuous pressure. Their tough skin is far less sensitive than that of horses and hence they can withstand tough weather conditions. Although smaller in size, a mule has tougher hooves. Interestingly, they also show a natural resistance to diseases and ticks. Even as plow animals, they are more favoured. 

The mule makes a unique sound that does not entirely resemble either horses or donkeys. The sound they produce is much like a donkey but also contains the whinnying characteristic of a horse. 

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Fertility of the Mule Horse 

The reason why mules are largely infertile lies in their crossbreeding. On its mother's side are horses with their 64 chromosomes. On the contrary, the jackass on its father's side has 62 chromosomes. As a result, the mule is born with an odd number of 63 chromosomes. Due to the varying structures and an odd number of chromosomes, they cannot pair up and this prevents the successful creation of embryos. Hence, the mule ends up being infertile. 

If we go by some ancient and antique texts, some mare mules are known to have given birth when bred with purebred horses or donkeys. However, this was generally seen as a bad omen. Ancient Greek texts have frequent records of mules giving birth, but modern scientists and researchers have questions on the truth of such claims. 

From 1527 to 2002, researchers have access to just about sixty documented cases of mules birthing offspring. Most recently in Colorado, scientists documented a mare mule giving birth to a colt. This incident happened in the year 2007. Blood sample testing from the parent and offspring confirmed their breeds and that they were mother and offspring. 

History of the Mule Animal 

The mule has a repute for being the most common and ancient man-made hybrid. Research suggests that mules first came around in ancient times in a place that is now modern-day Turkey. By 3000 BCE, mules were widespread across Egypt. In his ancient epic, the Iliad, Homer notes the arrival of the mules in Asia Minor in 800 BCE. The mules also find mention in the Holy Bible. While searching for the New World, Christopher Columbus was sailing with mules and hence introduced them to the North American continent. 

George Washington went on to become the Father of the American Mule. During his time at his home in Mount Vernon, Washington successfully produced fifty-seven mules. During Washington's regime, mules weren't that popular in the United States, but the President realized their worth, stating that they were better than donkeys and also cheaper to maintain. 

The nineteenth century saw a surge in the number of mules and how humans started using them. The mule earned its reputation as a capable draft animal and started being used on farms to plow the fields in which clay made the soil slippery, on decks to pull canal boats, etc. The mules were famously used between 1883 to 1889 to carry wagons of borax out of Death Valley in California by teams of twenty of these animals. These wagons hold the record of being the largest ever pulled by draft animals, each designed to carry nine metric tonnes of borax ore.

Modern Usage of the Mule Horse 

As the second half of the 20th century rolled out, industrialization led to a huge decline in the use of mules. The widespread usage of mules for farming and transport of agricultural produce also declined steadily with the arrival of steam and then gasoline-powered vehicles. 

However, even today, mules are in use in rugged areas where there are no roads and where man's vehicles do not work. In places such as California's Sierra Nevada mountains with their dense and vast wilderness, and the Pasayten Wilderness in the northern Washington state, mules are used to this day to carry cargo. These days mules are used commercially in several ways. They carry mountaineering base camps, assist in carrying maintenance equipment, and also help in carrying crew for footbridge construction, etc. According to numbers in July 2014, Sierra Nevada hosts a minimum of sixteen commercial mule pack stations. The Angeles chapter under the Sierra Club hosts a Mule Pack Section which offers mules to carry supplies in hiking trips. 

Mules have also contributed in times of war. During the Soviet-Afghan War, mules were sent to transport supplies and weapons to the mujahideen across Afghanistan's difficult terrain. 

In many parts of the world, mules also serve as food. Over three and a half million mules and donkeys get slaughtered every year for their meat. 

Mule trains have been a part of a working transportation system even as recently as 2005. 

Mule Trains

So what are mule trains? If we have a line of pack mules carrying cargo, irrespective of whether they're a connected line or not, we call them a mule train. The mule comes with several perks, such as its ability to carry as much weight as horses, while being sure-footed like a donkey and being able to sustain on cheaper and poorer foods, and also can survive in arid weather conditions. Due to all these plus points, mules have always powered animal-driven bulk transportation ever since the pre-classical era. The advantage of using a mule is that in a similar climatic and terrestrial environment, a pack of horses would need to carry much more fodder and grains and therefore could carry much less cargo. In modern terms, we see packs of reliable mules carrying riders into risky terrain such as canyons. 

Packs trains consisting of mules played an instrumental role in the opening of the American Wild West for trade and tourism. These determined and dependable animals can carry up to 110 kg, sustain themselves on rough fodder, battle difficult weather, and can even endure the high elevations of the Rocky Mountains. As a result, mules constitute the main form of cargo transport to the west from Missouri during the reputed North American fur trade. 


As we have seen, the mule is a very interesting and highly useful animal. With its double parentage of a mare and a jackass, the mule flaunts several qualities which have made it an indispensable resource for human beings for several years. The strengths and abilities of the mule are almost astonishing and they have proved their worth several times over time immemorial. There's still a lot more that one can learn about the mule, but one thing is for sure, that whoever decided to cross-breed a mare and a jackass did great service to mankind. 

Did You Know?

  • There's a phrase that says "stubborn as a mule", but research suggests that mules are in general extremely patient and intelligent. 

  • The first mule which scientists could successfully clone was called Idaho Gem, born in May 2003. 

  • We have a champion racing mule called Black Ruby who has won over 50 tournaments before she retired in 2008. 

FAQs on Mule

Q1. How Much Weight Can a Mule Ideally Carry?

Answer: Mules generally weigh between roughly 300 to 500 kg, although some draft males can weigh up to 700 kg. Mules can generally carry 30% of their body weight when it comes to living weight. This means some mules can carry a load of up to 160 Kg. However, how much weight a mule can comfortably carry is greatly determined by the superiority of its breeding. As a general rule of thumb, mules can carry up to 20% of their body weight in dead weight or cargo. This approximately estimates up to 90 kg for an average mule. Although a lot depends on the breed and individual characteristics of the mule, reports suggest that mules trained and used by the Army of Pakistan can carry over 70 kg of weight continuously at a stretch for over 25 km without resting. 

Q2. What are Estrus Cycles in Female Mules?

Answer: It is a well-established fact that mules are generally sterile and cannot give birth. However, a female mule that has estrus cycles can, in theory, carry a fetus. Such a female is called a Molly or a molly mule, although sometimes this term is used as an umbrella term for all female mules. Pregnancy in female mules is extremely uncommon but can sometimes take place naturally, and other times through organized mating or embryo transfer. There are some documented accounts of mare mules giving birth to a mule filly or a mule colt or even at times giving birth to a stallion. Historical accounts of such occurrences generally state them as an ill omen, while scientists find it hard to accept the accuracy of those events. 

Q3. In What Ways are Mules Better than Horses or Donkeys?

Answer: Mules are greatly favoured by animal herders and handlers because they exhibit qualities that are superior to that of both horses and donkeys. The mule is biologically an example of hybrid vigor, a term that refers to a hybrid offspring that possesses qualities that are advanced as compared to its parents. Mules are known to be more intelligent, they are known to have greater memory, endurance, muscle power, and social affection, while perfectly sustaining on lesser and lower quality fodder and maintenance. They are also known to be more patient, live longer, and have a natural resistance mechanism against diseases and infections.