Horses are closely related to donkeys, and although they have different looks and additional two chromosomes in the horses, they belong to the same family and genus, so they can easily interbreed and produce offspring. However, the offspring is normally sterile which means they can't reproduce.  A male horse and a female donkey offspring is called a hinny and a female horse and a male donkey offspring is called a mule. They are widely used as pack animals, transportation for people, farm animal, and even pets.