Equus caballus and equus assinus -- the horse and the donkey -- have quite a few differences besides ear length and a neigh versus a bray. The horse has 64 chromosomes, while a donkey has 62. They can, however, breed and create a hybrid, sterile equine. If the donkey's the dad, the result is a mule. If a horse is the sire, the foal is a hinny. Telling the difference between a mule and a hinny requires some equine expertise, but that's not the case with the parents.
Donkeys are often, but not always, smaller than horses. A donkey's tail is short, and the hair on the tail and mane is stiff. A horse's mane and tail is generally long and thick. A horse's coat is much smoother than the coarse hair of the donkey. A donkey's hooves are rounder and smaller than a horse's, but his head and eyes are proportionately larger. Unlike horses, who have ergots on all four legs, donkeys have them only in the front.
Horses appear in a variety of colors and patterns, but so do donkeys. Although the mousy grayish dun is the most common shade, donkeys might be black, brown, roan and chestnut. They generally have crosses on the shoulder, dorsal stripes, and a light muzzle, eye ring and abdomen.
Donkeys have a reputation for being stubborn, but they're really extremely cautious. Horses are "fight or flight" animals, but the donkey is more of a "let's check this out thoroughly" type. A horse often bolts when frightened, but even when afraid a donkey doesn't necessarily panic. Instead, he'll think about the proper reaction to the given situation.
While both horses and donkeys can be ridden and driven, a donkey's temperament and body structure doesn't afford him the same type of athleticism often found in horses. Their strong sense of self-preservation means they'll think twice before jumping tall fences or galloping across questionable terrain. Actually, galloping isn't really part of the donkey vocabulary. Donkeys don't need the constant schooling that horses often require when learning something new. They generally get it the first -- or at least the second -- time.
Mares have an 11-month gestation period. For jennies -- female donkeys -- gestation is a month longer, approximately one year from insemination to delivery. However, it's not abnormal for a jenny to carry a foal for up to 14 months. While twins are rare in either species, they occur more frequently in donkeys. A donkey isn't generally as fertile as a horse, but has a greater ability to convey hereditary characteristics to offspring.
A horse has an average conception rate of 60 to 65 percent, while the donkey's ranges between 50 and 60 percent. Mares bred to donkeys conceive at the same rate as when bred to stallions. That's not the case for jennies bred to stallions -- one reason there are far fewer hinnies than mules. The conception rate for jennies bred to stallions is just 25 percent.
With good care, a horse might live between 25 to 30 years, and sometimes longer. A donkey might live between 40 and 50 years, almost unheard of in a horse. A mule falls somewhere in between his parents, but the endurance they inherit from their donkey sire often enables them to work far longer than the average horse.