Health Concerns of Mules and Donkeys

The veteran mule breeder eyed me speculatively. I was there to pick up two mares that had been bred to his Mammoth jack.

"I hear you train horses," he said.


"Ever train a mule?"


He inclined his head toward the two pregnant mares. "Plannin' to train those youngsters after they're born?"

"I guess. Any reason I shouldn't?"

He thought a moment and said, "Mules is different."

"Tell me how they're different."

But, in the fashion of the stoical neighbor in Robert Frost's "Mending Wall," he wouldn't go much beyond that saying, "Mules is different."

As I was leaving, he suggested that I consider getting assistance from a knowledgeable mule trainer when it was time to break the youngsters.

Some years and the ownership of a number of pack mules later, I now recognize the veracity of that simple statement: "Mules is different."

Mules and donkeys are a lot like horses, to be sure, but in many ways, including some health concerns, they are most definitely different. First, we should have a basic understanding about what constitutes these unique four-footed creatures. We provide the following nomenclature with the help of the American Donkey and Mule Society.

Ass--The correct term for the animal commonly known as the donkey, burro, or jackstock. The term comes from the original Latin term for the animal that was Asinus. The scientific term for these animals is Equus asinus. The term fell into disrepute through confusion with the indelicate term "arse," meaning the human backside.

Jack--The term used for the male of the ass species.

Jennet--Pronounced JEN-et, it is the correct term for the female of the species. The most commonly used term is jenny.

Burro--A word taken directly from Spain. It means the common, everyday working donkey found in Spain and Morocco. More recently, it has come into common usage in the Western United States. As a general rule, the term burro is used west of the Mississippi and the term donkey east of the Mississippi.

Wild burro--These are the feral (descended from domestic stock, but gone wild through the years) donkeys which roam unfettered in parts of the Western United States.

Donkey--The word, taken from England, has an uncertain derivation. Most authorities think that the name comes from dun (the usual color) and the suffix "ky," meaning small. Thus, "a little dun animal."

Donkey sizes--Donkeys come in all shapes and sizes ranging from the Miniature Mediterranean Donkey that stands 36 inches or less in height to the Mammoth, where males must exceed 56 inches in height and females, 54 inches. In between are three categories of "Standard" donkeys.

Mule--The hybrid animal produced when a male donkey (jack) is crossed with a female horse. The mule is sterile. There have been isolated cases where a mare mule has reproduced, but that is a fluke of nature. The donkey jack generally will pass on its long ears, narrow body, and smaller hooves. The horse contributes size, speed, and muscle. The classic outward difference between a donkey and mule is the tail. The donkey has a tail like a lion or a cow-long tail with a tassel. The mule has a tail like a horse-short tail bone with long hair. The donkey also has a distinctive bray while the mule often seems to combine the bray and the whinny. When the mule gives voice, it starts out like a bray and ends in a whinny.

Hinny--This is the term for the hybrid animal produced when a horse stallion is mated with a jennet. Some hinnies tend to look like horses with long ears, but most can't be distinguished from mules. While hinnies do not differ in form, endurance, or temperament from mules, they are bred less frequently. One of the key reasons is that jennets do not seem to conceive as readily when bred to a horse stallion as when bred to a jack.

Horse mule--This is the proper term for the male mule. It is strongly recommended that all male mules be gelded, as stallion mules, although sterile, are sexually active. (I once owned a horse mule which had been gelded at an early age, but still was so sexually active that he was capable of getting an erection and penetrating a mare in heat.) Many people informally refer to the horse mule as a john mule.

Mare mule--This is the formal term for a female mule, although the common informal term is molly.

Mule colt or mule filly--These terms refer to the young male or female mule under three years of age.

Types--Mules (and hinnies) can be bred from any horse or pony breed. Therefore, they are listed by the using type rather than the size or breed of the horse parent. Included in the types are:

Miniature mule--Bred from various types of pony mares or Miniature Horse mares. The cutoff in size to be considered a miniature is 50 inches at the withers.

Saddle mule--Bred from mares of riding horse breeding. These vary in size from small to very large, but have riding conformation and looks.

Pack/Work mules--Bred from mares with some draft blood or of heavy work types rather than for saddle conformation.

Draft mules--These are the largest mules and are bred from various draft breeds. (One of the most popular crosses, in my observation, is the Belgian mare bred to a Mammoth jack.) The larger and heavier, the better with these mules, but refinement is desired as well.

Gaited mules--These mules are bred from gaited horses, including the Tennessee Walker, Missouri Foxtrotter, Saddlebred, Paso Fino, and Peruvian Paso. Gaited mules have their own registry--The American Gaited Mule Association.

With the above information as a base, let's take a look at some of the similarities and some of the differences among donkeys and mules and horses.

Basics Of The Beasts

Donkeys and mules differ somewhat from horses in conformation. The most noticeable aspect, of course, in-volves the ears. The donkey has the longest ears, while the mule seems to be about midway between the donkey and the horse. The necks of donkeys and mules are characteristically straighter than the necks of horses, and both have far less prominent withers than most horses. The croup and rump of the donkey and mule also have a distinctive shape, usually far less muscular in appearance than those of the horse.

The mane and tail of the donkey are coarse. The mane is stiff and upright, rarely lying over. The mule will have combination hair--usually a thin forelock and coarse mane hair.

Generally speaking, donkey hooves are smaller and rounder than those of a horse, and the pasterns are more upright. The feet of the mule fall somewhere in between horse and donkey. They often tend to be more like the feet of the horse, but are more upright and boxy.

Before we get into some of the other differences, especially those involving health concerns, we should address the delicate topic of temperament.

We all have heard, and perhaps used, the term "stubborn as a mule" or "stubborn jackass." This is a delicate topic, because the true mule aficionado will take instant and serious umbrage when mules are classified as stubborn brutes, while the person who has had only slight and passing contact with them will declare that the term is accurate.

Betsy Hutchins, secretary of the American Donkey and Mule Society, as well as a mule owner and exhibitor, has this to say on the subject of stubbornness:

"Mules are not stubborn. Neither are donkeys, for that matter. Too many mules and donkeys have been carelessly broken or not trained at all and are expected to know what to do and to obey immediately. Too many mules have been treated roughly and frightened when young, instead of made confident in their handlers. And, too many handlers have failed to take into account that strong sense of self preservation that a mule has. Yes, if you want him to work too hard for his well-being, especially in hot weather, he will be 'stubborn,' and, yes, if you try to frighten or hurt him, he will definitely be 'stubborn' and might even fight back."

Mules seem to have an inbuilt protection device that does not allow them to be worked beyond their capacity. There are horses which are so willing that they literally can be ridden to death. Not so, the mule. When it reaches a certain point of exhaustion, it simply shuts down and will go no farther until rested. To some this is classified as stubbornness.

The mule also appears to endure heat much better than the horse.

Hutchins tells this story:

"I will never forget a double show we attended here in Texas on a hot day. There were beautiful palominos in one arena and fine mules in the other. They were all performing in the same classes except that the individual mules would go in many classes, such as Western pleasure, barrels, single driving, coon jumping, halter, and probably egg and spoon and pole bending classes thrown in, whereas the horses were more specialized and only went in one or two classes in most cases.

"The thing that impressed everybody who noticed it was that the palominos were absolutely black with sweat. They were dripping, frothing, and drenched in it. I purposely examined most of the mules. They were sweating--under their browbands and saddlepads. The animals I had at the show drank one bucket of water each full day, and they each went in seven classes.

"If you looked around, you didn't see any mule owner hot-walking his animal. Only in really exceptional cases such as endurance riding or exceptional activity in very hot weather is a mule walked until cool. Most are turned loose to roll in the sand and cool themselves out."

A key difference between donkeys and mules when compared with horses involves water intake. Donkeys, and most mules, have a built-in mechanism similar to that of the camel in which the animal, when water starved, will drink only enough to replace lost body fluids while the overheated horse might drink until it becomes ill. Water founder almost never occurs in the mule.

A personal case in point. When we lived in Kentucky, it was a two-day trip to get to a western destination for a vacation of mountain riding and trout fishing. Our journey took us across the central part of the United States where soaring summer temperatures are common.

One of our pack mules, a lovely buckskin named Tammy, would not consume a single drop of water during the two-day trip. We tried all the ruses, such as flavoring the water and even bringing some from home. Nothing worked. When Tammy traveled, she didn't drink, no matter how hot the day.

She often wouldn't drink until we arrived at the first mountain stream after leaving a trailhead. She never guzzled water, even then, as though suffering from thirst. She merely drank normally and usually was finished well before the horses.

Another difference between horses and mules involves food intake. The average horse, when given free access to grain, will consume it in quantities that will endanger its health. While donkeys and mules are also capable of overeating and foundering, the number of instances will be far fewer when compared with horses, especially in the case of mules.

There appears to be a definite metabolic difference when comparing donkeys and mules with horses. For one thing, there is a difference in protein requirements. Donkeys have been known to founder after eating a single bowl of high-protein (about 27%) dog food. While many commercial horse rations are in the 16% protein range, donkeys and mules seem to do far better on a ration that has 10-12% protein.

Donkeys and mules, pound for pound, also eat less than horses. Generally speaking, when donkeys and mules are working, their grain ration should be about one-third that fed to a horse of similar size doing the same work. Donkeys seem to do best on good pasture with minimal amounts of grain as supplement.

When it comes to physical soundness, mules often seem to excel when compared with horses. They have strong, tough, flexible feet and many are never shod at all. Because they have small, upright, boxy feet, they also are very surefooted. Mules also seem to have fewer leg soundness problems than horses.

In an article entitled "Reconsider the Mule," Robert Miller, DVM, of California, a devoted mule fancier, wrote the following concerning a major mule event he had attended:

"And there are races. Mules run sprints ranging from 50 yards to a quarter-mile and races vary in length up to a mile. Although they are not designated race officials, at the finish line five veterinarians inspect the winners. They look at racing mules seven, eight, 10 years of age; many have been racing since they were two. Some are entered in many events each day. One mule runs several sprints and a mile race in a single day, in addition to barrel racing, stake racing, and a variety of regular show classes. Their legs are clean and sound. Not a splint or windpuff can be seen. There isn't a single big knee, a bucked shin, or an enlarged tendon. None are lame. Why? Why do they stay sound? Seeking answers, the veterinarians, all of whom are equine practitioners exposed daily to the tragedy of lameness in beautiful horses, look at mules, run their hands down the tough little legs and wonder."

One of the answers to the soundness question, it would seem logical to believe, involves hybrid vigor. Perhaps the tough physical and mental qualities of the donkey explain the rest.

Betsy Hutchins adds this thought: "The fact that they are inclined not to panic, to think about what is happening to them, and to take care of themselves physically prevents many accidents that might happen if they were horses."

Mules, as a rule of thumb, live longer productive lives than horses. In farming days, when an animal's value depended in part on how long it could work, it was often estimated that mules averaged 18 years of work compared to 15 for the horse.

A pamphlet published some decades ago titled, "Jacks, Jennets and Mules," which was designed to tout the stellar qualities of these long-eared animals, gave this report: "One of our members employs 160 mules in harness. He buys 3-year-olds and never sells one. When they become unfit for work, they are humanely destroyed. His records are exact. Of 89 mules in 1921, 28 were still at work aged 24 years in 1942. The average age of death of the 61 that had passed away (or had been put down) was 20 years."

Today, when mules are no longer asked to carry that type of workload and perhaps are recipients of superior nutritional and medical care, it is not uncommon to find useful lifespans of 30 years.

Surefooted To The End

Then, there is the matter of surefootedness. I can personally attest that there is no more surefooted riding or pack animal than the mule.

Betsy Hutchins explains it this way:

"The surefootedness of the mule is partly physical and partly psychological. The mule has a narrower body than a horse of the same height and weight. He gets this from the ass side of his family. His legs are strong and his feet are small and neat. This narrow structure and small hoof configuration enable him to place his feet carefully and neatly. His other advantage is psychological. Mules have a tendency to assess situations and act according to their views--most of which have to do with self-preservation."

Her comments recall to mind an incident when we were packing into the Beartooth Mountains of Montana. My lead pack mule at the time was a horse mule who was aptly named Rowdy. He had carried a very heavy load on the ride into the mountains and had settled into a workmanlike pace that was all business.

Because much of what he carried involved food and beverages that had been consumed, his load on the way down was much lighter. Without a heavy workload to occupy him, Rowdy became bored.

We were working our way down a mountain slope on a trail that was very safe. On the right was a very narrow ridge some three or four feet high and to the left was a gently sloping mountainside. However, on the other side of the narrow ridge was a river gorge. Jump over that ridge and you would be on a long death plunge.

I was riding along half asleep with Rowdy on a slacker-than-usual lead line when my wife let out a startled yell. I swung around in the saddle and there was Rowdy casually walking along the top of that ledge as though he were taking a Sunday stroll in the park. I quickly gave a hard jerk on the lead line and down he popped, with the guilty air of a child who had gotten caught with his hand in the cookie jar. He had been strolling in surefooted fashion, gazing down at the river, along a ledge that I never would have asked any horse or mule to negotiate. In fact, I would have declined to walk it on foot.

Health Concerns

When it comes to health concerns, mules are more like horses than are donkeys. Donkeys have more special health concerns.

One of these concerns involves lungworms. The equine lungworm (Dictyocaulus arnfield) is a major parasite of donkeys and a minor parasite of horses. Donkeys generally show no clinical signs of infection, but do pass larvae in their feces. The donkey is the natural host for the mature worm. Horses are considered abnormal hosts.

Many donkeys are infected early in life while grazing. Ingested larvae move through the intestinal wall and are carried to the lung, where they develop into adult worms up to four inches in length. The process takes two to four months, after which time eggs are laid. The eggs are carried to the throat by normal mucus production, then are swallowed and passed in the feces. Once deposited on the ground, they quickly hatch into larvae which, when ingested, begin the whole infective process again.

Surveys have shown that up to 70% of all donkeys are infected. One study at Texas A&M University found that 86% of the donkeys tested had lungworms.

Infected donkeys might not show outward signs of lungworm presence, but considerable damage can be done to lungs. Diagnosis of lungworm infection in donkeys can be done by fecal exam. However, special techniques usually are required. Horses pastured with donkeys are more at risk of being infected with lungworms than those pastured separately.

The good news is that lungworms can be treated effectively with certain dewormers (the one mentioned most frequently is ivermectin). It is advisable to treat donkeys every six to eight months with ivermectin, advises Frederick Harper, DVM, of the University of Tennessee. He also advises that, "If you get a donkey, have your veterinarian treat it with ivermectrin before placing it on your farm with horses."

In addition to lungworms, donkeys can be afflicted with the same internal parasites that attack horses and mules. If one is to tubeworm a donkey, however, special care must be taken. Suzanne Burnham, DVM, special consultant to the American Donkey and Mule Society, which is located in Denton, Texas, gives us this explanation of what can occur when passing a stomach (nasogastric) tube through the donkey's nostril and into the stomach:

"First, the donkey's ventral meatus, which is the appropriate starting place inside the nostril, is narrower proportionately than the horse's. A yearling or foal size tube should be used.

"Second, in the region of the larynx and pharynx there is a blind pouch caudally and dorsally (in a back and high position). This is called a diverticulum. This means that after the donkey has seemingly successfully just swallowed the tube into the esophagus, it suddenly meets a dead end and feels stuck. If it is jammed around and pushed, the donkey will resent any further attempt. The capillaries here are very fragile and excessive manipulation may cause the donkey to bleed from the mouth or nostril.

"Therefore, it is helpful to use a cold, stiff tube that will hold a curve rather than a very limber one. The donkey's head should bend down comfortably at the poll and he should not poke his nose upward. This will help bypass the blind pouch."

A unique health problem that can afflict donkeys is hyperlipemia. It is a serious problem that causes death in 60-85% of the donkeys afflicted. Stored body fat is implicated in the disease.

"The stored body fat is constantly being broken out of storage and placed into circulation," Burnham explains. "The liver processes fat--some is converted to useful substances and some is sent back into storage. If the body's demand for energy exceeds the supply, more fat will be broken out of storage than the liver can process properly. Too many lipids, triglycerides, and other related compounds are in the bloodstream and are trying to find organs to enter. Fat gets 'stuck' in the liver. This infiltration actually stretches the liver capsule and can be a source of pain. The liver, then kidneys, are affected. As the disease progresses, they cannot function properly."

One of the causes of the disease is fasting on the part of the donkey. Not eating for three to eight days can precipitate the problem.

About to 30-50% of reported cases, says Burnham, have a different primary disease such as colic or some other gastrointestinal problem, including parasites.

"Induced fasting as part of the treatment plan for laminitis may set it off," she says. "Sudden dieting to cure obesity may cause it to occur. Other predisposing factors include late pregnancy, abortion, or sometimes just lactation. Most of the reported cases have been female donkeys in foal."

Early in the process, the symptoms of hyperlipemia are vague. The donkey is lethargic, depressed, and has a poor appetite. Abdominal pain, variable increased rectal temperature, increased heart rate, and increased respiratory rate might be seen. As the disease progresses, incoordination, jaundice, bad breath, and ventral edema can be observed. In a few days, severe nervous dysfunction can occur. The afflicted donkey usually will develop diarrhea with mucus, will become recumbent, and might have convulsions. Pregnant jennies frequently will abort, usually in the terminal stages.

"Therapy," says Burnham, "should be aimed at treating the concurrent or primary stress--parasites, colic, or other disease. In some cases, a jenny will be induced to abort to save her life. Next, the energy balance should be restored with force feeding or IV fluid therapy correcting the glucose and acid levels as determined by lab tests. Frequent monitoring of blood values is very important. Antibiotics and vitamin therapy have been very beneficial. The use of insulin has shown variable success. Many of the affected animals are ill because of insulin-resistance, which may have caused the process in the first place. Insulin and heparin and nicotinic acid analogues are all drugs being tried at present, but no sure dosages have been established yet."

Prevention and early diagnosis seem to be key ingredients in preventing and/or treating the disease. Brood stock should not be allowed to get overweight, for example. If the affliction is suspected, an immediate test for triglyceride levels should be made.

External Parasites

External parasites, such as lice, often are more apt to afflict a donkey than a horse. One of the key reasons is that the horse sheds its coat in the spring while donkeys might retain a heavy, coarse coat on into the summer months, thus giving external parasites a better place to set up shop for a longer period.

A skin scraping taken by a veterinarian and examined generally will provide the source of the problem--lice, rainrot, ringworm, or whatever. It might be necessary to clip some of the long, coarse coat in order to treat the problem.


A basic difference between donkeys and horses is the gestation period. For horses, generally speaking, it is about 11 months. For the jennet, the normal span is 12 months and a number of females will carry their foals 13 months and still deliver a normal offspring.

An aspect of the donkey and mule personality that pet owners should be aware of is their natural aversion to dogs. In Wyoming and other Western states, it is not unusual to see a donkey or two roaming the range with a flock of sheep. If a dog or coyote appears near the flock, the donkey will run it off with snapping teeth and flashing hooves.

Mules which are exposed to dogs on a regular basis learn to tolerate them, but with donkeys, exposure might involve a longer period.

So, we can conclude that mules and donkeys need much the same care and attention to their well-being as horses, with a few extra concerns thrown in. If properly cared for and handled appropriately--especially in the case of mules--they can be excellent animals for a variety of disciplines.

Just remember, "Mules is different."

About the Author

Les Sellnow

Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at or by calling 800/582-5604.

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