Donkey
Donkeys can interbreed with other members of the family Equidae, and are commonly interbred with horses. The hybrid between a jack and a mare is a mule, valued as a working and riding animal in many countries. Some large donkey breeds such as the Asino di Martina Franca, the Baudet de Poitou and the Mammoth Jack are raised only for mule production. The hybrid between a stallion and a jenny is a hinny, and is less common. Like other inter-species hybrids, mules and hinnies are usually sterile. Donkeys can also breed with zebras in which the offspring is called a zonkey (among other names).
Elk
Until recently, red deer and elk were considered to be one species, "Cervus elaphus". However, mitochondrial DNA studies, conducted on hundreds of samples in 2004 from red deer and elk subspecies as well as other species of the "Cervus" deer family, strongly indicate that elk, or wapiti, should be a distinct species, namely "Cervus canadensis". The previous classification had over a dozen subspecies under the "C. elaphus" species designation; DNA evidence concludes that elk are more closely related to Thorold's deer and even sika deer than they are to the red deer. Elk and red deer produce fertile offspring in captivity, and the two species have freely inter-bred in New Zealand's Fiordland National Park, where the cross-bred animals have all but removed the pure elk blood from the area.