In the same family as horses and zebras, donkeys seem to get the short end of the stick when it comes to grace and majesty. Sturdy creatures, they are raised on farms around the world. First domesticated over 5,000 years ago, they’re relied upon in every corner of the globe. Each species of donkey has an elastic idea of its limitations – unlike species of sharks who don’t interbreed, or species of big cats that only do so under human intervention, donkeys breed willingly (in the wild and in captivity) within different species of Equus … and that’s not just with other donkey species!
The difference between a mule, a donkey and a hinnie
More than a dozen different species of donkey exist on six different continents – the one donkey-free continent being Antarctic, of course. There are some breeds of wild donkeys, while some are strictly domestic. Donkeys overall are known by a few names, including burros and asses. The males are called jacks and the females are called jennies, adding even more terms to the mix. Mules and hinnies, however, are not purebred donkeys. Both have one donkey parent, but are a mix of different species.
Donkeys have a slow reproductive rate. A jenny is pregnant for a full 12 months. Though she’s ready to go again within a week or two after giving birth, her fertility is low and, on average, it takes up to another two years before she’ll get pregnant again. Each birth usually only produces one foal. Twins aren’t unheard of, but they are rare. While producing foals is a difficult process, forming them is easy.
Donkeys are sexually indifferent. They’re not picky about their mate and will breed with a variety of partners. That includes donkeys in the wild. Besides within their own species and with other donkey species, donkeys can and often mate with horses. When a jack (a male donkey) mates with a mare (a female horse), the foal is called a mule. When a jennie (a female donkey) mates with a stallion (a male horse), the foal is called a hinny.
Mules are more common than hinnies because of two reasons
One is the sexual behavior of each species and the other is their chromosome count. Due to their indifference, jacks are more likely to want to mate with a mare than the other way around (stallions with jennies). Also, horses have a higher chromosome count than donkeys. When any male has a higher number of chromosomes than the female it mates with (as is the case with stallions and jennies), the rate of fertility is much lower than if they have equal chromosome counts. This means that both mules and hinnies are considered sterile, because of their uneven chromosome count.
In exotic cases, donkeys will mate with zebras! Their offspring has a variety of fun names: “zebroid,” “zeedonk,” and “zonkey” are all used. Those are the equivalent of mules. Zebra hinnies are a mixed breed born to a female zebra and a jack. They can also be called a zebret or zebrinny. These are even rarer than hinnies from donkey-horse pairings, as zebras are endangered and all reproduction for the sake of conservation is focused on breeding within the species. Meanwhile, there are plenty of donkeys in the world that can keep mating with plenty of horses.
Donkeys have 62 chromosomes, whereas horses have 64. Their resulting offspring therefore gets the average: 63. The foal’s 63 chromosomes are structured differently and unevenly, so that they won’t match up right for the sake of reproduction. This is especially true for male mules. There have been some cases in which female mules have given birth to a jack’s (pure donkey) offspring, but many of these are recorded in antiquity, raising doubt as to their reputability. Regardless, since the 16th century, there have only been about 60 cases reported across the planet of female mules producing offspring. Their validity is irrelevant when you consider how very small a number it is. It all points to mules being more than likely sterile.
Mules and hinnies are sterile
There aren’t any cases of producing offspring from two mules. The only recorded success humans have had with mating a mule is by breeding a female one with a jack. This doesn’t take donkey breeding in developing countries under consideration though, as it is possible mule-mule pairings have been bred, just not recorded. Genetics and biology seem to hint at it being highly unlikely, though.
The reason why both mules and hinnies are considered sterile (even though there has been rare evidence contrary to this fact) is because of the infinitesimal likelihood of either developing a fully-functioning reproductive system. The uneven number of chromosomes in a hinny can make the animal unable to produce sperm or eggs (depending on its gender), making fertilization all but impossible. Considering the fact that hinnies in general are rare, plus the fact that they’re extremely unlikely to be fertile, it’s safe to say they’re reasonably regarded as sterile.
From the Brothers Grimm to Shrek – with many writings, illustrations, and films in between – donkeys are a popular symbol in art and culture. They’ve also carried the world on their backs from Nicaragua to Ethiopia to Turkmenistan. Known by many names and mixed in a variety of ways, donkeys are a reliable, versatile, docile, and absolutely adorable animal.