Mules result from the mating of a horse and a donkey. While donkeys and horses are closely related, they are different species. Some of the differences between horses and mules are obvious, such as physical appearance. But, as the Alberta Donkey and Mule Society puts it, "Mules are not long-eared horses."
Horses and donkeys both belong to the genus Equus. The horse is Equus caballus, while the donkey is Equus asinus. Ponies and horses are one species, although their sizes are considerably different. Donkeys also vary greatly in size, so how large a mule will be when fully grown depends on the size of the parents. Draft mules, a cross between a draft horse and a large donkey, are huge equines, while miniature mules, a cross between a miniature horse and a small donkey, are tiny. Mules are easily produced in sizes suitable for the type of work they are intended to perform.
To produce a mule, a female horse is bred to a male donkey. If the breeding is the other way around, a jennet bred to a stallion, the offspring is called a hinny. It's not easy to tell the difference between a mule and a hinny, but the hinnies are often somewhat more horse-like in appearance.
Mules and hinnies are sterile; they cannot produce offspring. This is a fundamental difference between a horse and a mule or hinny. This is a consequence of the fact that their parents are each of different species. A fact that defines and differentiates species is that animals of different species, even if the species are closely related, cannot produce fertile offspring. Mules are bred for one purpose: To perform work. The cross between a horse and a donkey produces offspring that possess what is termed "hybrid vigor." Mules generally possess excellent performance qualities of health, endurance, toughness and strength, beyond what either horses or donkeys generally possess. This has made mules highly valuable to humans for thousands of years.
Rarely, a female mule breaks all the rules and gives birth to a foal. If one does, it's such an extremely rare event that it makes national headlines and biology textbooks. Mules have an odd number of chromosomes, 63, while horses have 64 and donkeys have 62. In such rare but confirmed cases, mule females bred by donkeys have produced a donkey foal, while those bred by a horse have produced a baby horse. It's as if the female mule's own genetic contribution didn't exist. No case of a male mule siring offspring has ever been reported. However, sterile doesn't mean lack of the impulse to breed, so male mules are gelded.
Mules generally live longer than horses. Horses may live into their 30s, but mules often live into their 40s. Their working lives are longer, as well. It's unusual for horses in their 30s to still be ridden or driven, at least more than lightly. Mules of the same vintage might still be working relatively regularly.
Mules are usually tougher than horses. Their feet are stronger than those of horses, and less likely to need shoeing. Mules' surefootedness is legendary, and it's the reason they're the animal of choice to ride or use for packing on steep mountain trails. Hybrid vigor tends to give mules the best qualities of both parents. Veterinarian Robert M. Miller, a mule breeder, says the hybridization "accounts for his amazing strength and stamina."
Whether mules are more intelligent than horses is somewhat subjective, but because they inherit a strong sense of preservation from the donkey side of the family, they react differently to perceived threats. Miller states that when horses are frightened, they will usually panic and flee blindly, often injuring themselves in the process. "A frightened mule, on the other hand, will usually assess the situation, and avoid injuring himself," according to Miller. This is a generality, and all horses and mules are individuals.
Mules are generally lower-maintenance equines than the horse side of the family. A mule eats about one-third less per day than a horse of comparable size and workload. Like donkeys, who developed in arid parts of the world, they have less need for water than horses do. That means they can work longer in hot weather, or go on longer rides or drives without needing as frequent rehydration. If they're not working, you don't need to feed them grain. Mules are less prone to laminitis or colic than horses are, as they don't tend to overeat if given the opportunity. They do well on basic forages such as grass hays.
- Rural Heritage: Why Mules?
- U.S. Department of Transportation: Understanding Horses and Mules
- Alberta Donkey and Mule Society: Mules Are Not Long-Eared Horses
- Rural Heritage: Horse + Donkey = Mule
- Denver Post: Mule's Foal Fools Genetics
- Tennessee State Library and Archives: Got Mules?
- Alberta Donkey and Mule Society: A Vet Suggests -- Reconsider the Mule
- Rural Heritage: Mule or Hinny?
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