Donkey vs Mule: Key Differences in Size, Ears and Behavior

Key differences at a glance

A donkey is a domesticated descendant of the African wild ass, bred in northeast Africa about 7,000 years ago. Donkeys mate with donkeys and produce more donkeys.

A mule is the offspring of a jack (male donkey) and a mare (female horse). It is a first-generation hybrid, and because it is almost always sterile, every mule has to be bred from a donkey and a horse. The opposite cross, a stallion with a jenny (female donkey), gives a hinny, which is less common and usually smaller than a mule.

People often call any long-eared working animal a donkey, and in some places “mule” is used loosely too, but the two are biologically different animals.

Size and build

Donkeys range from miniature animals under 90 cm (35 in) at the shoulder to large breeds such as the American Mammoth Jack and the French Poitou at around 1.5 m (59 in) or a little more. Most standard donkeys are about 91–122 cm (36–48 in) tall and weigh roughly 180–260 kg (400–575 lb).

A mule’s size depends mostly on its mother. Miniature mules from small pony mares can stand under 1.25 m (50 in), while draft mules from heavy horse mares reach about 1.8 m (70 in). Many riding and pack mules weigh around 370–460 kg (820–1,000 lb). So a typical mule is clearly bigger than a typical donkey, though a giant Mammoth Jack can be larger than a small mule.

In build, a donkey has a straighter back, narrower body, upright mane and very small, upright hooves. A mule usually has a horse’s height, neck and body shape, with the donkey’s thinner legs, short mane and narrow, tough hooves.

Ears, tail and coat

The ears are the quickest clue. A donkey’s ears are very long relative to its head. A mule’s ears are also long, much longer than a horse’s, but usually shorter than a donkey’s. A hinny tends to have shorter ears still.

Look next at the tail. A donkey has a cow-like tail: short hair along most of its length and a tassel at the end. A mule usually has a full tail of long hair like a horse’s. Hinnies, on the other hand, often have a tufted, donkey-like tail.

Donkeys are mostly gray-brown, brown, black or white, often with a dark cross on the back and pale muzzle and belly. Mules can be any color seen in horses or donkeys, including bay, chestnut, black, gray and spotted, and many show donkey traits such as a pale muzzle, a dorsal stripe or faint stripes on the legs.

Voice: bray vs whinny-bray

A donkey brays, making the famous “hee-haw” on both the in-breath and the out-breath; Why do donkeys bray? explains how and why. A horse whinnies.

A mule’s call usually blends the two. It often starts as a whinny and finishes in a hee-haw, and it varies a lot between individuals. Many mule owners can tell their animals apart by voice alone.

Temperament and intelligence

Donkeys have a reputation for stubbornness, but the trait is better described as caution. When a donkey senses danger, it tends to stop, look and think before acting, instead of running away like a horse.

Mules inherit much of this caution, together with a horse’s size and speed. They are known for being sure-footed on steep, narrow trails, which is why mules carry visitors and supplies down into the Grand Canyon. Mules also have a reputation for intelligence and for refusing to be pushed into anything they judge unsafe. A small 2009 study by British researchers found that mules learned a visual discrimination task faster than horses and donkeys, but scientific work on mule cognition is still limited.

Both animals form strong bonds. Donkeys usually pair up with a companion, while mules often attach themselves to a horse, especially a mare, and in pack strings will follow a lead mare closely.

Fertility: donkeys breed, mules almost never do

Donkeys have 62 chromosomes, horses have 64, and a mule has 63: 31 from its donkey father and 32 from its horse mother. The mismatched chromosomes cannot pair properly when the body tries to make eggs or sperm, so mules are almost always sterile.

Male mules never produce working sperm. Female mules occasionally conceive, but only about 60 births to mare mules were reported between 1527 and 2002. Read the full story in Can mules have babies?.

Donkeys, by contrast, breed normally. A jenny is pregnant for about 12 months and usually has a single foal.

Work, strength and lifespan

Donkeys are the world’s most widespread working equid. There are roughly 50 million of them, mostly in Africa and Asia, where they carry water, wood and goods and pull carts. They need less food than a horse of the same size and cope well with heat and drought.

Mules combine the donkey’s toughness with a horse’s size and power. Pack mules commonly carry loads of up to about 90 kg (200 lb), and historically they hauled freight, plowed fields and served in armies. George Washington promoted mule breeding in the United States after the American Revolution, and the famous twenty-mule teams of 18 mules and 2 horses hauled borax out of Death Valley, California, in the 1880s. Today Mexico has the largest mule population in the world.

Both animals live a long time. Well-kept donkeys usually live 25–35 years, as described in How long do donkeys live?, and mules are known for similar or longer working lives, often 30 years or more.

Which is better?

Neither is simply “better”; they suit different jobs. A donkey is cheap to keep, hardy, long-lived and ideal for small loads, dry climates and as a livestock guardian or companion. A mule is stronger, taller and faster, and is preferred for heavy packing, riding over long distances and mountain trails. The trade-off is that mules cannot reproduce, so people who rely on them must keep breeding donkeys and horses to make more.