A pack animal, also known as a sumpter animal or beast of burden, is an individual or type of working animal used by humans as means of transporting materials by attaching them so their weight bears on the animal's back, in contrast to draft animals which pull loads but do not carry them.

The mule is a domestic equine hybrid between a donkey and a horse. It is the offspring of a male donkey and a female horse. The horse and the donkey are different species, with different numbers of chromosomes; of the two possible first-generation hybrids between them, the mule is easier to obtain and more common than the hinny, which is the offspring of a male horse and a female donkey.