Horses and donkeys are often confused with each other because they are similar creatures. Each is also often confused with the mule, which is the interbred offspring of a female horse and a male donkey. While horses and donkeys have many similar characteristics, there are also key differences between these two large, four-legged mammalian species.
Both horses and donkeys are in the same scientific genus, Equus, which means they come from a recent common ancestor. However, they are different species. The horse is Equus ferus, while the donkey is Equus asinus. Because they are very close to each other, genetically and evolutionarily speaking, they have the potential to interbreed. Like other species that share a genus, such as dogs and wolves or chimpanzees and bonobos, they look similar and have similar habits.
On the surface, horses and donkeys look the same. They have similar body types, walking on four legs and with a long tail in the back. Their heads are similarly shaped with eye and ear placement, as well as a mane along their necks. However, horses tend to have longer faces. Depending on the breed, their sizes vary, but in general horses are larger than donkeys. However, donkeys have larger sexual organs, which is important for breeding purposes.
Another similarity that horses and donkeys have is their use by humans. Because they are both sturdy animals, they are often found on farms for labour purposes. Donkeys are common beasts of burden, and still do many of the tasks for which they have been used for thousands of years. Both horses and donkeys are also kept as pets, although horses, especially thoroughbreds, are more commonly used for show and as racing animals.
Because they are genetically similar, horses and donkeys can be crossbred. The most common result is when a female horse and a male donkey have an offspring known as a mule. The less common result is when a male horse and a female donkey have an offspring known as a hinney. Both mules and hinneys are sterile. This is a result of the horse's having 64 chromosomes and the donkey's having only 62. While their reproductive cycles are very similar, they differ slightly, such as the donkey's having a slightly longer gestational period.
Horses and donkeys eat similar foods and can survive on the same diet. Because of domestic breeding, however, horses have a more refined digestive system. Because donkeys have been used throughout the centuries to transport goods over long distances, they have developed strong immune and digestive systems. They are adapted to grazing and foraging for food, offering them a high-fibre diet of plants that are not always ideal for nutrition. Horses primarily eat grains and have a higher resting metabolism than donkeys.