The Real Differences Between Mules and Horses

Saddle mules take a break at Indian Garden in the Grand Canyon. Photo by author.

Mules have a reputation. They’re stubborn, they’re hard to train, and of course they’re only good for pack work. (When people remember they exist, which some fantasy and historical fiction writers are bad at).

But we’ve been breeding mules since at least Roman times, so clearly they have their uses. Let’s talk about some of the real differences between mules and horses.

They’re Infertile — Mostly

You’ve heard the saying “Once in a blue moon.” The Romans had a different saying for a vanishing rare event, “A pregnant mule.”

Because horses and donkeys have a different number of chromosomes, mules generally can’t produce viable offspring. (This, btw, is the likely origin of an assumption that turned out to be incorrect…that species can’t interbreed). John (male) mules are routinely castrated to make them easier to handle.

Molly (female) mules generally can’t get pregnant. However, there have been extremely rare exceptions to this rule documented. The foal can even end up looking like a horse or a donkey. In fact, in 1939, a mule produced two offspring. The first, sired by a jack, was a sterile molly. The second was a colt from a Saddlebred stallion who looked like a horse, exhibited absolutely no donkey characteristics, and sired a number of foals. It appears that Old Bec, the mule, passed on only her horse genes. Somehow. Because mule pregnancies are so vanishingly rare, there’s a lot we don’t know about them.

An increasing number of molly mules, however, are giving birth and raising foals. It turns out that mules are amazing mothers and thus they are now being used as surrogates for high quality mares who have reproductive issues…or simply so the mare can continue to compete and breeders don’t have to choose between showing and breeding her before she gets too old).

Pack string in the High Sierras. Mules aren’t ONLY for pack, but they are pretty good at it. Photo by author.

They Need To Drink Less Often

Ride a horse all day in hot weather without watering it and then give it water? You might kill it. Horses get something called water founder when they become dehydrated and then…