Mules and Donkeys

AAEP added a new dimension at the annual convention this year. An entire afternoon session was devoted to a discussion of mules and donkeys. The fact that Tom Lenz, DVM, president-elect, was in charge of the program might have had something to do with it--Lenz is from Missouri, a state long noted for its mule population. Lenz moderated the session, telling the large crowd in attendance that he would have a hard time explaining himself back home if he hadn't featured mules and donkeys on the program. The mule, he said, is Missouri's state animal.

In the wake of his introduction, four speakers set forth to explain the many intriguing attributes of the long-eared critters. One message seemed to pervade all of the presentations--you often can't transfer what you know about, and do with, horses, to mules and donkeys.

Leading off the session was Suzanne Burnham, DVM, of Burnham Veterinary Hospital in Graham, Texas. Burnham is a mule owner and has given numerous presentations on mules and donkeys.

"Very little of what is known about the mule comes from scientific research," she said. "Folklore and muleskinners teach us that a mule is a creature of habit; that mules enjoy a good roll at the end of the day's work; and that mules recover from a hard day's work faster than a horse."

People handling mules through the years have learned to work around their peculiarities without injury, she said, and while scientific knowledge might be lacking, veterinarians should learn from muleskinners.

"Veterinarians who work around mules," Burnham said, "need to be wary because mules are very agile; a mule can strike with any other hoof even if a man is holding one up. Veterinarians need to be patient and work quietly and gently around a mule, but they need to work with purpose and conviction. For the veterinarian working on mules, it is not only important to be a good horseman, but also to know the ways of a good muleskinner."

She also offered this bit of advice, which was almost a warning: "Donkeys and mules are exceptionally revered by their owners, and in recent years, in some parts of the world, their value has increased to equal or exceed that of the horse. These owners are looking to you (the veterinarian) for competent advice."

Burnham then provided her listeners with a bit of a history lesson. In 1785, she said, George Washington sought to purchase a good jack (intact male donkey) from Spain. He was told that the King of Spain had forbade the exportation of jacks. However, when the King heard that Washington wanted a good jack to produce work mules, he relented and sent a jack and a jennet (a female donkey) to Washington as a gift.

The following year, Burnham said, the Marquis de Lafayette sent Washington a Maltese jack, which became an excellent sire of mules. Thus, she said, Washington played a major role in the development of the mule industry in America. By 1840, Burnham told her listeners, a quality jack used for mule breeding could sell for as much as $5,000 in Kentucky, a state more known for its Thoroughbreds, but still a leader in mule production.

Because mules vary so much in genetic makeup, she said, they do not make good subjects for scientific research. (A mule results from breeding a donkey jack to a mare. Conversely, the offspring resulting from breeding a stallion to a jennet is known as a hinny.) Because of the genetic diversity of mules, she said, we must turn to the study of the donkey in an effort to understand both mules and donkeys.

"What do we know about donkeys and how do they differ from horses?" she asked rhetorically. "A donkey brays and has long ears, but those are not the only differences. He has a completely different outlook on life, drinks water differently, reacts to frightening situations differently, has very different nutrient requirements, and has some unique physiological responses. For instance, the normal ration for a horse will make a donkey obese, possibly cause him to founder, and may result in decreased fertility."

Burnham then described some physical differences between donkeys and mules versus horses. In addition to long ears, she said, donkeys have a short, upright mane and have finer, lighter hair around the eyes and muzzle when compared to horses. Donkeys have no forelock and have a switch for a tail. Mules normally will have a full tail, but might not have a forelock. The hair in the flank of a donkey has no upward whorl as is the case with horses, and the donkey has chestnuts only on the front limbs. Mules will have half a whorl on the flanks and variable chestnuts. Donkeys have small, boxy hooves with thicker hoof walls than does the horse. The hoof angle is also more upright. And, of course, donkeys bray while horses nicker or whinny.

The reason they bray, says Burnham, is because there are key differences in the anatomy of the larynx and pharynx when compared to the horse.

Another difference, she said, involves a donkey having heavy muscle covering the jugular furrow, which can make it difficult to draw blood or to administer drugs intravenously.

There is also a difference in the number of chromosomes. "The diploid number of chromosomes for the domestic horse," she said, "is 64. For the domestic ass, it is 62, and for the Asiatic wild ass, it is 54 to 56. Gestation for the domestic horse ranges from 335 to 346 days, and for the domestic ass, it is 365 to 370 days."

Donkey Reproduction

D.G. Pugh, DVM, MS Dipl. ACT, Dipl. ACVN, of Auburn University, continued the discussion on donkey reproduction. Pugh raises donkeys on his Alabama farm.

Both the male donkey and the male mule, he said, have penises and testicles that are a good deal larger than the horse. One peculiarity noted when breeding with donkeys, he said, is the longer time it takes for the jack to achieve an erection and ejaculate. Jacks, he explained, usually need five to 30 minutes in the breeding process, compared to 10 to 11 minutes for the horse.

Because of the large size the donkey's and mule's testicles, it was pointed out by Burnham in her presentation, care must be taken when castrating them because of the potential for copious bleeding. "Castrating the donkey or mule by the routine method used in horses--without ligation (stitches)--may result in excessive bleeding, and some have died as a result," Burnham explained.

The jennet, Pugh told his listeners, is similar in many reproductive aspects to the horse mare, but there also are differences. For one thing, he said, donkeys seem to display less seasonality than mares. Puberty in donkeys usually is attained between one and two years of age. The jennet's cervix is usually longer than that of the mare, Pugh said, with a smaller diameter. The donkey cervix, he pointed out, protrudes into the vagina, and this protrusion might preclude intrauterine ejaculation, make artificial insemination more difficult. He said the anatomy might be associated "with a high incidence of post dystocia cervical adhesions."

Jennets, he added, seem to be more prone to dystocia than horses, probably because they don't have delivery muscles that are as strong as those in the horse.

Anesthesia of Mules and Donkeys

Nora Matthews, DVM, Dipl. ACVA (anesthesiology), of Texas A&M University, discussed how donkeys and mules differ in their reaction to anesthesia when compared to horses.

"In many ways," she said, "donkeys are more like cattle; stoic about not showing distress and pain and easier to restrain (than a horse) with hobbles or ropes if securely applied. Many procedures could probably be performed in donkeys with sedation and appropriate use of local anesthesia as is common in cattle. It is, however, a major mistake to underestimate their intelligence; they are very capable of fighting effectively when not outnumbered, and they are very canny about recognizing when they are."

The donkey, she said, might have a greater capacity to metabolize certain drugs. This can mean in some instances that donkeys will require more of the drug or need to have it administered at shorter intervals to maintain effective drug concentrations.

Mules, she said, seem to be either the intermediate between donkeys and horses or closer to the horse in their response to drugs.

When it comes to inhalant anesthesia, she said, donkeys and mules seem to respond about the same way as horses. However, she said, the stoic nature of the donkey seems to allow it to recover from the anesthesia without trauma or excitement.

"Our usual procedure," she said, "is to simply leave donkeys unattended, but not unobserved, in recovery." She showed a film of a donkey recovering from anesthesia. The donkey was in sternal recumbency and was nibbling at grass around it. Finally, it simply stood up without a struggle.

"They almost never fall down," Matthews said. "They're too smart to attempt to get up until they are able to stand."


The final speaker was Tex Taylor, DVM, Dipl ACVS, of Texas A&M University. Taylor breeds mammoth donkeys at his farm.  Mammoth donkeys are animals that stand more than 14 hands. With tongue in cheek, he told his listeners that he was going to present a talk on "Assology."

There has been a change in health concerns for mules and donkeys --especially mules--in recent years, he said. Prior to the 1960s, he explained, mules were working animals from draft-type mares and sired by draft-type jacks. Most of the work they did, he said, was done at a walk and trot, and in a straight line. Rarely were they required to work at speeds greater than a walk.

That all changed, he said, when draft mules and horses were replaced by tractors. In recent years, the mule has been tapped for various performance events and activities in the equine recreational world.

Today's mules, Taylor said, are produced from saddle-type performance horses and sired by smaller, more refined jacks.

"We are asking the mules to duplicate the maneuvers of our racehorses, roping horses, reining horses, driving horses, cutting horses, and others," he said. "We have changed our expectations of our mules as well as their pedigree. We are infusing all of our lameness predispositions into our mules and following up with the appropriate training programs to insure development of the same lamenesses seen in horses."

Because of a higher tolerance for pain on the part of the donkey and mule, he said, lamenesses are often advanced before the animal demonstrates a degree of lameness that demands examination and treatment. Also, because of this higher pain tolerance, he said, hoof testers often aren't as valuable a diagnostic tool as they are with horses.

Restraint of mules (and to a lesser degree donkeys) often requires a two-phased approach. "First," he said, "you have to keep the mule in the general vicinity where you plan to treat him." This could require use of a small pen, a chute, stocks, a snubbing post, or the use of swinging gates or panels. Once the animal is so confined, he said, a twitch, war bridle, scotch hobble, or foreleg strap can be used as further restraint. It has been his experience, he said, that the foreleg strap which imprisons a front leg by folding back at the knee with the hoof strapped to the upper foreleg, is a highly effective restraint.

When using any restraint appliance other than the twitch, Taylor said, time should be allowed for the mule or donkey to get used to it before the practitioner proceeds with treatment.

He added this warning: "With mules, it is very important that you get it right the first time. Unsuccessful attempts to restrain a mule are positive rewards for bad behavior that rapidly become learned skills."

Taylor also pointed out that severe respiratory distress in donkeys demands immediate treatment. Donkeys, he explained, often have severe secondary bacterial infections after or along with equine influenza virus. The same problem is not seen in mules, he said.

When donkeys are removed from the herd setting and treated for a malady or injury, he said, one must be aware of the strong bonds that exist between an individual and the herd. He described one of his mammoth jennets which had been injured and was being kept in a stall as part of the recuperative process. She stopped eating and nothing worked to entice to begin eating again. Finally, he said, he simply returned her to the pasture and her companions.

"She walked over to that hay bale, started eating, and never looked back," he said.

The speakers also pointed out that mules and donkeys on the average live longer than horses, with some reaching 45 years of age.

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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