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Old hinny in Oklahoma.jpg
Scientific classification edit
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Perissodactyla
Family: Equidae
Tribe: Equini
Genus: Equus

Equus mulus[citation needed]

A hinny is a domestic equine hybrid that is the offspring of a male horse (a stallion) and a female donkey (a jenny). It is the reciprocal cross to the more common mule, which is the product of a male donkey (a jack) and a female horse (a mare). The hinny is distinct from the mule both in physiology and temperament as a consequence of genomic imprinting.


Hinnies are the reciprocal cross to the more common mule. Comparatively, the average hinny has a smaller stature, shorter ears, stronger legs, and a thicker mane than the average mule. The distinct phenotypes of the hinny and the mule are partly attributable to genomic imprinting—an element of epigenetic inheritance.[1]

Physiological arguments for the differing stature of the hinny and the mule cite the smaller womb of the female donkey (dam) versus the larger womb of the female horse (mare). Growth potential of equine offspring may be influenced by the size of the dam's womb. The American Donkey and Mule Society (ADMS) appears to interpret these differences as wholly physiological, stating: "The genetic inheritance of the hinny is exactly the same as the mule."[2] Be that as it may, the epigenetic inheritance of the hinny is not the same as the mule, as "the differences between the mule and the hinny are now known to be caused by genomic imprinting, whereby the expression of a gene is determined by its origin rather than its DNA sequence".[1]

Like mules, hinnies express broad variation in stature. This is because donkeys come in many sizes, from miniatures, as small as 24 inches (61 cm; 6 hands) at the withers, to American mammoth donkeys that may be over 15 hands (60 inches, 152 cm) at the withers. Thus, a hinny is restricted to being about the size of the largest breed of donkey. Mules, however, have a female horse as a parent, so they can be as large as the size of the largest breed of horse, such as those foaled from work horse mares such as the Belgian.[citation needed]

Physical differences between hinnies and mules are not restricted to stature. The head of a hinny is said to resemble that of a horse more than it does a mule's, with shorter ears (although these are still longer than those of horses), and more horse-like manes and tails than mules.[2]

Beyond the physiological, hinnies and mules differ in temperament despite sharing nuclear genomes. This, too, is believed to be attributable to the action of imprinted genes.[3]

A male hinny is properly called a horse hinny, and a female hinny is properly called a mare hinny, though in British English both female hinnies and female donkeys are sometimes called jennets.[2]

Fertility, sterility and rarity[edit]

Hinnies are difficult to obtain because of the differences in the number of chromosomes of the horse and the donkey. A donkey has 62 chromosomes, whereas a horse has 64. Hinnies, being hybrids of those two species, have 63 chromosomes and are in nearly all cases sterile. The uneven number of chromosomes results in an incomplete reproductive system. According to the ADMS: "The equine hybrid is easier to obtain when the lower chromosome count, the donkey, is in the male. Therefore breeding for hinnies is more hit-and-miss than breeding for mules."[2]

The male hinny or mule can and will mate, but the emission is not fertile. Many have no sperm in the emission, others have sperm that is not motile.[4] Male hinnies and mules are usually castrated to help control their behavior by eliminating their interest in females.[citation needed]

Female hinnies and mules are not customarily spayed, and may or may not go through estrus.[4] Though there have been claims that female hinnies have given birth, credible documentation is lacking.

Female mules have been known, on rare occasions, to produce offspring when mated to a horse or donkey, although this is extremely uncommon. Since 1527, sixty cases of foals born to female mules around the world have been documented.[5] For example, in China, in 1981, a mule mare proved fertile with a donkey sire. When the Chinese mule was bred to a jack, she produced the so-called "Dragon Foal", which resembled a donkey with mule-like features.[6] In Morocco, in 2002, a mule mare bred to a donkey sire produced a male foal.[5] DNA testing revealed the foal has a mixed karyotype hybrid like the Chinese hinny offspring "Dragon Foal".[citation needed]

Hinnies are rare for many other reasons. Donkey jennies and horse stallions can be choosier about their mates than horse mares and donkey jacks.[citation needed] Thus, the two parties involved may not even care to mate. Even if they do cooperate, donkey jennies are less likely to conceive when bred to a horse stallion than horse mares are when bred to a donkey jack. Breeding large hinnies is an even bigger challenge, as it requires stock from a jenny of large size, such as the Baudet de Poitou or American Mammoth Donkey. Mammoth donkey stock is becoming increasingly rare and has been declared an endangered domestic breed. Fanciers are unlikely to devote a Mammoth jenny's valuable breeding time to producing sterile hinny hybrids, when Mammoth jennies are in high demand to produce fertile purebred Mammoth foals.[citation needed]

See also[edit]


  1. ^ a b Hunter, Philip (2007). "The silence of genes. Is genomic imprinting the software of evolution or just a battleground for gender conflict?". EMBO Reports. 8 (5): 441–443. doi:10.1038/sj.embor.7400965. PMC 1866201. PMID 17471258.
  2. ^ a b c d "Longear Lingo". lovelongears.com. American Donkey and Mule Society. May 22, 2013. Retrieved 2014-07-16.
  3. ^ Wang, Xu; Miller, Donald C.; Harman, Rebecca; Antczak, Douglas F.; Clark, Andrew G. (2013). "Paternally expressed genes predominate in the placenta". Proceedings of the National Academy of Sciences. 110 (26): 10705–10710. Bibcode:2013PNAS..11010705W. doi:10.1073/pnas.1308998110. PMC 3696791. PMID 23754418.
  4. ^ a b Zong, E; Fan, G (June 1989). "The variety of sterility and gradual progression to fertility in hybrids of the horse and donkey". Heredity. 62 (3): 393–406. doi:10.1038/hdy.1989.54. PMID 2753743. S2CID 25057091.
  5. ^ a b Kay, Katty (2002-10-02). "Morocco's miracle mule". BBC News. Retrieved 2009-02-05.
  6. ^ Rong, Ruizhang; Cai, Huedi; Yang, Xiuqin; Wei, Jun (October 1985). "Fertile mule in China and her unusual foal". Journal of the Royal Society of Medicine. 78 (10): 821–25. doi:10.1177/014107688507801006. PMC 1289946. PMID 4045884.

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