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About Equine Crosses, Mules, and Other Hybrids

I'm a horse rider, role-playing gamer, and science fiction and fantasy fan. I've also been married for 15 happy years.

Picketed mules waiting to go.

Picketed mules waiting to go.

Equine Hybrids and Crosses

It's a saying for a reason—mules are smart and more inclined to let their handler know their opinion than horses.

Mules are not the only equine hybrids created. For a while, it was very fashionable to breed crosses between zebras and horses or zebras and donkeys. However, mules have been in consistent use for a very long time.

Why do we breed hybrids? What purpose do they serve? How, for that matter, did humans realize that if you put a donkey and a mare together they will breed a hybrid?

The history of equine hybrids may be longer than we think.

Ancient Equine Hybrids

One possible source for the idea of making hybrids takes us right back to Africa. Where the ranges of the wild ass and the zebra overlap, some natural hybridization occurs. It is possible that humans observed that these hybrids had the qualities of both species and took that knowledge with them.

Horses were first domesticated in the Asian steppes. Donkeys were likely domesticated in the Middle East. However, there is little evidence of when the two were first put together. A mule skeleton is not significantly different from that of a horse without DNA testing.

One possible indication is an equine that was found at Pompeii that was first identified as a new breed of horse by one expert, then later re-classified as a donkey. A third expert opined that it might be an 'exotic hybrid'. I think it far more likely that it was a non-exotic hybrid - a mule. In Greece, several breeds of pony are perpetuated solely for use in breeding mules, indicating that the creation of mules likely began somewhere in the eastern Mediterranean area. In Spain, the mammoth jack breed of donkey was created and perpetuated solely for the purpose of breeding larger mules than could be produced with standard-sized donkeys.

A mule is the result of a jack (male donkey) breeding with a mare. A hinny is the result of a stallion breeding with a jenny (female donkey).

A mule is the result of a jack (male donkey) breeding with a mare. A hinny is the result of a stallion breeding with a jenny (female donkey).

Donkey and Horse Mix

A mule is the result of a jack (male donkey) breeding with a mare. A hinny is the result of a stallion breeding with a jenny (female donkey).

Mules Versus Hinnies

Relatively few hinnies are bred. The reason for this is not because hinnies are inherently less useful, but because they are harder to create. Fertility rates from stallion x jenny matings are lower because it is harder to breed a hybrid if the chromosome numbers are lower in the female (horses have 64 chromosomes while donkeys have 62).

Hinnies are generally indistinguishable from mules and the only known way to tell them apart without knowing the pedigree is to turn them out with a mixed group of donkeys and horses and see which they hang out with - they will tend to gravitate towards the species of the mother. This is not entirely reliable, however.

Mule Gender and Fertility

It's well known that mules are infertile. Some laymen may think that mules are also neuter (genderless). This is not true—mules and hinnies both come in male and female 'models'. Male mules are called johns, females are mollies.

Are mules always infertile?

Mules are, however, almost always infertile. There have been a few, extremely rare, cases of molly mules turning out to be fertile. In one case, a molly mule, Old Beck, produced a colt foal that appeared to be entirely horse. Named Pat Murphy, Jr., he proved to have normal fertility when bred with horses and sired a number of pure horse foals.

It's generally considered that john mules would not be fertile, based off of evidence of species crossing in certain cats that results in fertile females and infertile males. However, the hypothesis has never been fully tested as john mules are routinely castrated at an early age to reduce testosterone levels (which are normal in mules) and thus make them more tractable.

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Minis and Mammoths

The majority of mules bred in America are crosses between mammoth jack studs and either stock horse or draft mares. These can produce mules as big as seventeen hands and a draft mule can pull considerably more than a comparably sized horse. The cross between a mammoth jack sire and a Belgian dam is so popular it has its own name - Missouri Mule. (The red mule in the picture is a Missouri mule).

Some mules are also bred using standard sized donkeys (called burros in the west) and pony or small stock horse mares.

As both miniature donkeys and miniature horses exist, it is inevitable that there would also be miniature mules, which some people like to keep as pets or to pull small carts.

Why Do We Make Mules?

So, why make mules in the first place? What advantage does a mule have over horses? There are several:

  1. Mules are more tolerant of heat and need less water than horses. Horses are a cold steppe animal, whilst donkeys are naturally adapted to the desert. Mules tend to take on the donkey adaptation and are less likely to suffer from heat exhaustion. This is why mules (as well as asses and burros) have been historically used in the desert southwest and are still valued there today.
  2. Mules have a different power to weight ratio from horses. A 50" standard mule has been known to jump a 72" fence carrying a pack...from a standing start. (Mule shows often include classes called 'Coon jumping', in which the winner is the mule that clears the highest fence from standing in a marked area). As a general rule, mules are more powerful than horses.
  3. Some people prefer the intelligence and somewhat different mind and temperament of a mule over a horse.
  4. Mules can actually be safer to ride in dangerous situations as they rarely bolt. A frightened horse can lose its mind completely - this rarely happens with mules or donkeys.
  5. Mules have donkey style feet that rarely need to be shod. They are generally more surefooted, although I admit I have ridden well trained horses on trails I would not want to walk.
  6. Mules eat less than a comparably-sized horse and are thus cheaper to keep.
  7. Mules have greater endurance than the average horse and also live somewhat longer.
5 Disadvantages of Mules

5 Disadvantages of Mules

5 Disadvantages of Mules

So, what are the disadvantages of having mules?

  1. Mules do have a different mindset. Although they are not as stubborn as the stereotype, they think more like a donkey than a horse. Horses react. Mules take initiative, and this can make the transition from working with horses to working with mules difficult for a rider and handler.
  2. Mules are infertile, and sometimes by the time you work out a particular mule is of exceptional quality it is too late to repeat the original cross.
  3. Normal horse saddles do not always fit mules. They have a different shoulder and sometimes need a special mule saddle. They also need a special bridle called a 'mule headstall' that is fastened behind the ears.
  4. Although mules are generally easier to feed than horses, they do not tolerate high protein or high energy feed.
  5. If you anger a mule and it kicks you, it is more likely to do you real injury than a horse. Mules will also kick out with their front feet, which horses generally do not, and they are more likely to cow kick (kick forwards with the hind leg).

Okay, But What About Those Zebras?

In 2001, a zoo in England bought a Shetland pony mare from another zoo to use in their petting zoo. They were shocked when she kept putting on weight despite a diet and the vet informed them she was pregnant.

They called the first zoo who swore up and down they had no intact male horses on the premises. A few months later out popped a foal - with stripes. (I am not clear on the details of just how the zebra got in with the mare or vice versa).

Zebra Hybrids

Zebra hybrids are sometimes bred in order to try to create something with the mindset of a domestic animal and the stripes of a zebra. Unfortunately, this is not an exact science and zebroids can be difficult to handle.

It is, actually, possible to train and use a pure zebra, but zebras lack a certain key part of the anatomy - they have no withers. Zebras are also very small. Hybrids are generally bred to be larger. Zebra hybrids are extremely quick in both their movements and reactions and are not recommended for novices.

Most zebra hybrids come from a zebra stallion that was hand raised or raised with domestic horses to make him easier to handle (Zebra mares are too valuable for captive breeding of pure zebras to be used).

© 2012 jenniferrpovey


Amanda from Michigan on March 13, 2015:

I am so happy that I stumbled across this article! I have never personally worked with mules but recently I have been coming across videos and articles about mules now being used in Dressage! It is quite an amazing connection. I would imagine it would take quite a bit of patience to work with a mule because they think so differently, but I am sure the rewards would be well worth it.

Silver Poet from the computer of a midwestern American writer on February 02, 2012:

I used to own a mule. She was a very smart animal. Jumping mules are wonder in the way they can leap a fence from a stand still. Thanks for writing this.

jenniferrpovey (author) on February 02, 2012:

Some people are breeding Arabian mules for endurance riding now. A mule, Coyote Waits, qualified for the Pan American Games in 1999 in that sport and completed the 100 mile race against horses (although he did not win).

Special shows called 'mule days' are held all over the country, in which mules compete both under harness and in saddle, including in jumping, dressage, western dressage, trail, barrel racing, steer name it, and people will do it with a mule (many of these shows also have donkey classes).

I don't work with mules myself, but I thought it would be fun to highlight that they aren't just for carrying packs and pulling loads.

Paradise7 from Upstate New York on February 02, 2012:

This is interesting and well-written. I always thought of mules as draft animals, for use in pulling plows. I never thought of mules as animals that a person rides. So, I learned something new today. Thanks!

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