A dzo (Tibetan མཛོ་ mdzo tso) is a male hybrid of a yak and domestic cattle. A female offspring is known as a dzomo or zhom. Alternative Romanizations of the Tibetan names include zho and zo. In Mongolian it is called khainag (хайнаг). There is also the English language Portmanteau word of yakow; a combination of the words yak and cow, though this is rarely used.
Dzomo are fertile, while dzo are sterile. As they are a product of the hybrid genetic phenomenon of heterosis (hybrid vigor), they are larger and stronger than cattle or yak. In Mongolia and Tibet, khainags are thought to be more productive than cattle or yaks in terms of both milk and meat production.
Dzo can be back crossed. As a result, many supposedly pure yak or pure cattle probably carry a dash of each other's genetic material, respectively. In Mongolia and Tibet, the result of a khainag crossed with either a domestic bull or yak bull is called ortoom (three-quarter-bred) and an ortoom crossed with a domestic bull or yak bull results in a usanguzee (one-eighth-bred).