A zonkey is a cross between a zebra and a donkey. The generic name for crosses between zebras and horses or asses is zebroid or zebra mule. "Zonkey" is not the technically correct name for such a cross. The most commonly accepted terms are zebrinny, zebrula, and zedonk. Donkeys are closely related to zebras and both animals belong to the horse family. Zonkeys are very rare.
In South Africa they occur where zebras and donkeys are found in proximity to each other. Like mules, however, they are genetically unable to breed, due to an odd number of chromosomes disrupting meiosis. However, in The Origin of Species, Charles Darwin reported a case of a zonkey that apparently bred with a bay mare to produce a "triple hybrid".
Usually a zebra stallion is paired with a horse mare or ass mare, but in 2005, a Burchell's Zebra named Allison produced a zonkey called Alex sired by a donkey at Highland plantation in the parish of Saint Thomas, Barbados. Alex, born April 21, 2005, is apparently the first zonkey in Barbados.
Breeding of different branches of the equine family, which does not occur in the wild, results in infertile offspring. The combination of sire and dam also affects the offspring. A zebrinny is the offspring of a male horse and a female zebra; a zebrula is the offspring of a male zebra and a female horse; a zedonk is the offspring of any zebra and any donkey.
A number of hybrids, described as Zeedonks, were kept at Colchester Zoo, the product of accidental mating; the last died in 2009. One adult and a foal remain at the tourist attraction of Groombridge Place  near Tonbridge in Kent.
The Wild Animal Safari in Springfield, MO has several zedonks as of March 31, 2010.
Donkeys and wild equids have different numbers of chromosomes. A donkey has 62 chromosomes; the zebra has between 32 and 46 (depending on species). In spite of this difference, viable hybrids are possible provided the gene combination in the hybrid allows for embryonic development to birth. A hybrid has a number of chromosomes somewhere in between. The chromosome difference makes female hybrids poorly fertile and male hybrids sterile due to a phenomenon called Haldane's Rule. The difference in chromosome number is most likely due to horses having 2 longer chromosomes that contain similar gene content to 4 zebra chromosomes.
Common wisdom states that hybrids only occur when the zebra is the sire, but the Barbados hybrid demonstrates otherwise. Two other known zebra hinnies have been foaled but did not survive to adulthood. The rarity of zebra hinnies indicates that the smaller number of chromosomes must generally be on the male side if a viable hybrid is to be produced. Before this comes into account, a successful mating needs to be accomplished in the first place though: As courtship in horses involves the mare kicking at the stallion's head for some time before allowing him to mount, and as this behavior is stronger in wild equids than in domestic horses, it is difficult enough to get a horse stallion to mate and not be put off by the rough behavior of the non-horse mare.
Zonkeys are interspecific hybrids bred by mating together two species from within the same genus. The offspring have traits and characteristics of both parents. Zonkeys vary considerably depending on how the genes from each parent are expressed and how they interact.
- Tijuana Zebra
- ↑ Megersa, B.; Biffa, D.; Kumsa, B. (2006). "A mysterious zebra-donkey hybrid (zedonk or zonkey) produced under natural mating: A case report from Borana, southern Ethiopia". Animal Production Research Advances 2 (3): 148–154.
- ↑ "Call it zonkey or a deebra? Zebra has a foal sired by a donkey". Associated Press. MSNBC. 29 Apr 2005. http://www.msnbc.msn.com/id/7677651/. Retrieved on October 13, 2008.
- ↑ Colchester Zoo (2009-04-03). "Colchester Zoo mourns the loss of Shadow the Zeedonk". Press release. http://www.colchester-zoo.com/index.cfm?fa=news.press.detail&Press_Release_ID=244.
- ↑ "The Enchanted Forest". Groombridge Place Gardens. http://www.groombridge.co.uk/enchanted.htm.
- ↑ K. Benirschke, et. alia (1964). "Chromosome Studies of a Donkey-Grevy Zebra Hybrid". Chromosoma 15 (1).
- "Zenkey foal a hybrid star". Sydney Morning Herald. Agence France-Presse. 29 Aug 2003. http://www.smh.com.au/articles/2003/08/28/1062050609625.html.
- "Hybrid Equines". messybeast.com. http://www.messybeast.com/genetics/hybrid-equines.htm. Photos of ass-zebras from the 1930s.