Posted on March 19th, 2018
I wanted to write a nice little article on mules, explaining them to those who know horses. There is plenty of conventional wisdom on the subject, but on closer examination it all seems to be the same, and seems to distill down to not much at all. There is not much science at all comparing donkeys, mules, and horses, and many of the topics covered here deserve better than they have been given. And the little science that has been done reveals that some of this conventional wisdom is dangerously wrong. Direct observation can help fill in the gaps, so when there was no science that I could find, I’ve resorted to telling you about my new love, my mule named Freckles.
The domestic horse (Equus caballus) and the donkey (Equus asinus) are members of family Equidae – “equids” – that last shared a common ancestor 1.9–2.3 million years ago. All equids can interbreed and produce vigorous hybrids1, as can many species that diverged so recently. And they seem to enjoy it. Burros are small donkeys, perhaps a breed but not a distinct species. The terms “ass” and “jack ass” refer to the donkey (and sometimes this author). “Zorse” and “zonkey” refer to crosses with zebras.
When a female horse (mare) is crossed with a male donkey (jack), the result is a mule (Equus asinus × Equus caballus); when a male horse (stallion) is crossed with a female donkey (jenny), the result is a hinny. Mules and hinnies are usually sterile, but not always.2 Mules and hinnies inherit the same genetics, and any difference is usually that of size. Both the size of their father and the size of their mother’s womb contribute to a mule or hinny’s size, so coming from a (typically) smaller mother, the hinny is usually smaller than the mule. Mules have been called humanity’s first successful experiment in genetic engineering.
If they were normally fertile, horses and donkeys would not be different species, since “species” is usually defined as the largest group of organisms from which two individuals can produce fertile offspring. But fertility has nothing to do with lust. Female mules (mares) experience the same hormonal surges as do female horses and donkeys and riders; male mules (stallions) are always full of desire, whereas gelded mules are usually half-full. When my mare mule walks by a pasture of gelded horses, they all stare and show off the way we non-gelded boys did in high school, when a Senior girl walked by.
Because a mule is a joint product of horse and donkey, it would seem that they should be an average of the two: mid-way in height, vigor, sense of humor, etc. But the laws of combination don’t favor averaging. They seem to favor weighting and multiplication.
- With weighting, a mule would normally turn out more like one parent than the other. Mules seem more like their fathers when it comes to courage, but because they are larger, they likely are even less fearful. They may also be more like their fathers in preferred diet, reacting to pain, independent thought, strength and stamina, and disposition. Mules have the large white muzzle, wide eyes, long ears, and stiff mane of their donkey fathers, and the long face of their mothers. In mules, body size is “female dominant.”
- With multiplication, a mule would come out better than either parent. Hybrid vigor or “heterosis” (the tendency of a crossbred individual to show qualities superior to those of both parents) accounts for why mules are smarter, healthier, and more long-lived than either of their parents.
Mules have been described as the animal without “pride of ancestry, nor hope of posterity”3. But there is ample reason for pride of ancestry, for a mule can show the best qualities of both parents. Hybrid vigor is the result of outbreeding dissimilar parents – the opposite of the effects of inbreeding suffered by some monarchs. Hybrids are typically fitter than either parent. In the world of dogs, crossbreeds may live longer than pure breeds4 and be able to run faster than their parents5. Hybrid vigor also applies to mules, and they are noted for having sounder feet, fewer medical troubles, and longer life spans than horses.
If you have grown up with the horse as a baseline, you will be stunned when you get to know your first mule. When I’d owned her just a month, I took my mule camping for three days in the mountains. Some of the rocky trails we used had steep sections that could have been traversed by humans only by crawling or hanging on to trees to get up or down safely. We spent our first two days going up and down these trails. On our third day in the mountains, we entered a 17 mile Endurance ride. Without any electrolytes or special treatment, Freckles motored through this too. I am overwhelmed by her stamina.
Hybrid vigor in the mule extends beyond endurance. Compared to horses, they are less prone to sickness and disease. Have tougher hooves. Live around ten years longer – many can be ridden until they are 40 or so. Pound for pound, they seem stronger, and are the normal choice for pack trains or pulling canal barges. Got a 40 ton load that needs pulling over 165 miles in Death Valley? Twenty mules can do that.6
One writer sums it up well: “Mules have greater size, more endurance and stress tolerance, longer work life, and survive on poorer nutrition than their parents. Mules do not overeat or overwork to exhaustion as horses do. Mules have a more acute sense of self-preservation.”7
Those who know both mules and horses are likely to claim that the mules are smarter. But we’re here for an education, and claims don’t count for much.
A study done in the UK which compared horse, mule, and donkey on a discrimination learning task found that mules performed much better than horses or donkeys, learning faster.8 In a study in which equids had to navigate a simple maze, mules learned the route significantly faster than horses or donkeys. When the maze was changed, the researchers found that the mules and donkeys were more flexible in their behavior than the horses, who continued to try the route they had previously learned.9
In another study, “Six of each animal were shown sets of two food buckets, each marked with a different symbol.In order to gain access to the food, the animals had to pick the correct bucket. The mules learned to discriminate between more pairs of symbols than the horses or donkeys, and did so more consistently.”10
As I said, those who know both mules and horses are likely to claim that mules are smarter than horses, but the evidence they offer usually comes down to a few standard observations:
- Thirst. a thirsty mule will drink only enough to replace its lost fluids, while a horse might overdrink, and water founder.
- Hunger. A mule will generally eat what it needs, even if there is an abundance of food available. Miners liked mules because they could leave them for three days with a three day food supply. A horse would have consumed three days rations in two days.
- Refusing to overwork. There are many stories of overloaded mules refusing to move, but when the load was lightened a bit, moving readily. And many stories of mules simply stopping when they’d had enough. Horses may be more eager to please, and more likely to nearly die from exhaustion.
- Quick to bore. Mules seem to bore more quickly than horses in most any task, and need shorter sessions if you are going to teach tricks. Intelligence probably makes boredom happen sooner.
If we are to make any inference from the little science we have, we might suspect that mules are smarter than either parent, and that their fathers are smarter than their mothers. We need much more science here, but more thought and discussion as well: if a mule is “smarter” than her parents, what must she do to prove it? And what if we could prove that a mule was smarter than a horse in some ways: Just how smart is that? And where has this debate gotten us? Horses and mules and donkeys are plenty smart. They are smart enough.
Differences in Appearance
Mules look just like horses, apparently. When Freckles and I meet strangers, I’m likely to hear “What a pretty horse!” (I never hear the stranger say anything to her about me.) But a more careful look reveals many differences. Mane and tail are longest in the horse, shortest in the donkey, and intermediate in the mule. Hooves are largest in the horse, smallest in the donkey. Limbs are thinner in donkey and mule than horse. Donkeys have a straight horizontal back, mules have a slight downward curve, and horses have a substantial curve. Horses have withers, donkeys don’t and mules take after their dads enough that you may need special precautions to keep your cinch/girth from riding up into their armpits. And they don’t call mules and donkeys “longears” for nothing.
Get up close, and you’ll find more differences. The mane of the donkey and mule is not merely shorter than that of a horse, but it is stiffer too, and stands up no matter how long it has grown. Donkey nostrils are smaller than those of the horse. Donkeys and most mules don’t have the horse’s forelock. Pick up their feet, and you’ll be amazed: donkeys and mules have thick strong hoof walls, and small feet. You’ll likely never see the hoof with a chip or crack.
When you compare a similarly sized horse and donkey side-by-side, you’ll see that proportions differ. The donkey has a relatively larger head, with a much larger nasal bone, a thicker, denser, larger mandible, larger nasal cavity, and larger brain case11. Teeth differ, too, with the donkey’s molars more closely resembling human molars.
There are many differences between horses, mules, and donkeys under the hood. A useful summary is provided by Stephen Purdy.12
There is great variation in the size of donkeys and horses, and so great variation in mule size. Donkeys range from “miniature” (about 6 hands at the withers) to over 15 hands, as in the case of the American Mammoth Donkey. The average mule may be about the height of a typical Arabian horse – around 15 hands (60 inches). My mule is 14.3 hands, about the height of a typical mustang. Most mules grow to nearly the height of their mothers.
Horses and donkeys evolved in different environments, and their inner workings reflect this. While the horse was busy dining in grasslands, donkeys likely evolved in arid, desert-like conditions. As a result, digestion in donkey and horse differ, as do food-related behaviors.
Evolution in arid regions forced it to snack on brush and bark, and gave the donkey its powerful jaws. Donkeys evolved to browse and graze and to get by on nutrient-poor food. Given free choice of what to eat, they are likely to be found snacking on dry grass, bark, leaves, twigs, acorns and roots. Donkeys need twiggy foods, and would often prefer straw to hay.
Pound for pound, donkeys eat less than a horse, and need less protein. Where an overweight horse has spread this weight evenly about his body, a donkey will carry it in his crest, rump and pannier region. Given a pasture of alfalfa or lush spring grass, any equid might develop laminitis. But unlike a foundering horse, a donkey will not take a laminitic stance (rocked back, to keep the weight off the inflamed laminae at the front of the hoof). Donkeys generally don’t get enough to eat in the third world, and laminitis is not much of a problem there. But in your barn, experts warn that donkeys should never be given grain, perhaps because they seem to eat faster and may be liable to esophageal obstruction.13
Horses and donkeys evolved differing approaches to water, too. Donkeys can abstain from drinking, and can work hard even when dehydrated. It has been reported that donkeys can lose 30% of their body weight through dehydration without adverse effects, and that they can rehydrate by drinking within five minutes14. When they are given water, they may guzzle. Horses can’t safely abstain or guzzle. Donkeys and mules are less likely than horses to water founder, and seem fussier about the water itself. My mule will not drink from the streams that my thoroughbred was happy to drink from.
From Lisa Preston’s exceptional book on equine nutrition we learn “In the developed world, overfeeding is the greatest nutritional threat facing most donkeys… Donkeys easily overfeed when placed on pasture. They have relatively low protein needs, doing well on straw and … corn stalks … to meet their forage-chewing needs. Horse people can be reluctant to use straw as feed, equating it to poor forage, but a donkey does not need higher quality grass and legume forages.”15 Mules may be more like donkeys than horses when it comes to dining. Treated like a horse, my mule gained weight rapidly. Now, she gets no forage or grain in her stall, just hay and straw in separate hay racks on her wall, and she is free to choose what she eats. Where a horse would never choose the straw, she often does.
When they are finished with dinner, donkeys and mules place their poop in a neat little pile at the wall of their stall – like a stallion’s stud pile, whereas horse mares and geldings behave as if they were not planning on ever lying down again.
Donkeys seem to have boundless courage, and a donkey is often added to a herd of beef cattle in South America, to guard the cattle against jaguars. The evident courage of the little donkey may come from its evolution to fight, rather than flee. This must be how Donkey (in the Shrek movies) got all his courage.
When Freckles and I were on one of our first trail rides together, we were attacked by a large German Shepherd. As the dog charged at us, I expected that I would soon be trampled by my stampeding mule. Instead, Freckles faced it, standing calmly and waiting. At the last second, she reared to kill it. The dog swerved and ran off. Freckles returned to the ground, and we resumed our walk. My gal protected me in the same way her dad might have protected a herd of cattle.
My thoroughbred’s fear impacted his every action on a trail ride. Normally, he would be stressed in a good breeze, and balk at wooden bridges, downed trees, mud puddles, steep banks, stream crossings, or even some new trash along a familiar route. He would freeze or take flight at leaping deer, leaping egrets, low-flying hawks, flapping plastic bags, charging dogs. Sometimes, I think he was back at the barn before I hit the ground. My riding style with him involved a lot of preparation to avoid going over the handlebars on a sudden stop.
My mule balks at nothing because of fear. If Freckles encounters a fallen tree on the trail, she’ll simply step over it or jump it without even slowing. If she encounters a silly jump in an arena, she just walks through it. If our route on the trail takes her to a puddle she’ll go around. If the puddle goes all the way across the path, she’ll motor through it. If it takes her to a steep bank up or down, she’ll simply tractor up or down.
On the other hand, we disturbed a woodchuck yesterday, who went running toward his burrow for safety. That happened to mean that he came running in our direction, and Freckles decided we’d better avoid this predator. We made a swift U-turn. On another occasion, we jumped a 4′ downed tree very nicely, but our descent triggered my air vest with a loud explosion, and Freckles decided we’d better flee these hunters. So she has concerns, and she deals with them. But I am yet to be embarrassed by her judgment. She has always kept me aboard and kept me safe.
Good judgment, good talent, and good courage, if you ask me.
Courage comes from more than a heritage of not running away from trouble. It also comes from knowing where your feet are, where to put them, and how to put them there. I’ve encountered many reports that “a mule, like a donkey, can see all four feet while facing forward, but a horse facing forward can see only its front two feet because of head shape”16 This seems to be a common opinion, but I haven’t found anything that smells like science on this, and I don’t think it is true. What seems more likely is that a mule monitors the changing surface as it passes over it, and remembers the terrain briefly, allowing it to visualize that terrain as its feet reach it, and allowing it to choose where it is putting its feet17. We do this with two feet; doing it with four doesn’t require a change in skull shape – just an improved set of cognitive skills.
What a mule can do with four feet is amazing. The Grand Canyon experience is probably adequate proof of this. Depending on the route taken, the distance from rim to river is about one mile, so a trip to the bottom and back is two miles of elevation change. According to one source, “Since the mule trains started traveling the canyon in 1922, no mule has ever gone over the side. Through the years, more than 800,000 mules and riders have made the trip down and up without a mishap.”18 800,000 trips with a 2 mile elevation change is 1,600,000 total miles of altitude change on narrow, rocky trails. That’s around the earth 64 times.
But “without a mishap” is likely a small exaggeration. I found a story about a mule that fell on a canyon ride and rolled over his passenger, injurying her.19 But this one injury compares with the 770 people who have died in the Grand Canyon while not on a mule.20
You should spend some time looking at YouTube videos resulting from a search of “extreme mule”. It is hard to imagine any other animal carrying a human over this stuff. Climbing a pile of loose rocks takes more than a good pair of sneakers.
Mule skinners – those who can “skin” or “outsmart” a mule21 – have called mules “900 pounds of free enterprise.” And Harry Truman, a U.S. President who grew up with mules, once said “My favorite animal is the mule. He has more horse sense than a horse. He knows when to stop eating — and knows when to stop working.”
Mules can’t be bribed. My horse learned clicker training and target training in a single session, soon learned a dozen tricks, and over our decade together probably scored a thousand pounds of sliced carrots. When I met my mule Freckles, I discovered she didn’t want a carrot slice. Didn’t want an apple. Didn’t want a grape. Didn’t eat most of her grain. At first, I thought this was a defect in her early education, one which experience would overcome. But I’ve tried. While she will sometimes take a snack when offered, she is as likely to turn it down.
It is difficult to coerce a mule, too. I tied Freckles to a fence post the other day while I went into a pasture to visit with another horse. When I came back, Freckles had untied herself, but was standing calmly exactly where I’d left her, waiting for me. Go figure.
Clicker training doesn’t work if you can’t find a reward to give the click meaning. So we aren’t working on our tricks these days. But Freckles can do every single obstacle on any obstacle course, mounted or in hand, pausing at the obstacle or proceeding through it or backing through it. It makes me happy to think that I’m not the boss, and that I’ve partnered with so much free enterprise.
Reacting to Pain
Pain is one of mother nature’s ways of guiding behavior, and there is no reason to think that any equine would be exempt from it, or not experience it. Equids all benefit from not putting sharp objects in their eyes or lounging on barbed wire. So it is not in pain, but in the expression of pain that humans and equids differ. Humans seem very articulate at such expression, but equids remain quiet when the same disturbances affect them. Some of this silence comes from our own deafness, not being able to “read” the signals that our horse is sharing. But most of the silence likely comes from the nature of all living non-human things, who avoid predation by not revealing injury, and who do not live in the company of those who could help if they knew that help was needed. It is true that there are stories about dolphins and dogs helping each other, but the wild world usually works to hide injury.
Horses do, in fact, reveal pain with their facial expression. Horses and People has published a number of reports on the “Equine Pain Face” and the Horse Grimace Scale22. And horses may reveal pain with their behavior. They may show restlessness, agitation, and anxiety; they may assume a rigid stance, and be reluctant to move; they may lower their heads, hold a fixed stare with dilated nostrils and a clenched jaw; and they may show aggression toward handlers, other horses, and themselves. But in a summary of nineteen studies, researchers found that none of these signals is evident or easily detected in a donkey.23 Mules seem to acquire much of their father’s toughness. Mules and donkeys will almost certainly experience pain the way you and I and horses do, but are less likely to reveal it.
This does not work to their advantage. Studies of equine health in underdeveloped countries typically find high rates of wounds in working equines, particularly in donkeys and mules24. Something is not right when over half of the animals examined have obvious wounds.
Adapted to Heat, Not Cold
Donkeys adapt to the heat, in part, by letting their body temperatures rise. In one study, body temperature in cool early morning hours was as low as 35.5°C, (95.9°F). Body temperature reached its maximum at noon, at 39.0°C (102.2°F) with ambient temperature ranges of 16–40°C (60–104°F)25. In one study in which donkeys were dehydrated for 36 hours and then walked for 12 hours in the desert at a rate of 70-80 meters/minute, body temperature did not rise above 39.2°C (102.2°F)26
The cold, on the other hand, may pose more hypothermia problems for donkeys than horses.27 Conventional “wisdom” says that mules and donkeys are tough, and can handle the cold just fine28. But a donkey’s evolution in hot places should not lead to such a conclusion, and some research points to hypothermia risks for donkeys in temperate climates. Researchers in Saskatchewan29 studied admissions of horses and donkeys to their veterinary hospital, and concluded that donkeys were more likely than horses to be suffering from hypothermia. Their analysis found that the hypothermia was apparently unrelated to diet, disease, or management.
Britta Osthaus30 and her colleagues studied the hair coat properties of donkeys, mules, and horses in four seasons in the UK. They found that the hair weight per square inch – a clever way of measuring how thick a coat is – changed through the seasons for horses and mules, but not for donkeys. Horses and mules grow a winter coat, but donkeys do not. While mules grow winter coats like their mothers, in this study the coats were not has thick as those of horses. Per square inch, mule coats were always lighter than those of horses, but the difference was greatest in the winter. The table below simplifies their findings of hair weight in mg. per square centimeter.
Horses, mules, and donkeys may all need blanketing in the winter. Donkeys may need it the most, because they don’t grow winter coats and because their smaller mass generates less heat. Mules don’t grow winter coats as lush as those of horses, and may need blanketing more than horses do.
Strength and Stamina
There is no doubt that equines are strong, and common lore has it that donkeys and mules are particularly strong. According to one source, oxen and buffalo can pull a load that is 12% of their body weight, camels can pull 18%, and donkeys can pull 24%31. This topic quickly gets off into the weeds with discussions of tractive effort, foothold, grade, duration, resistance, training, etc. Larger equines can pull more than smaller ones, and the record pulls in one competition were 7,700 pounds for a mule team, and 10,500 pounds for a horse team32. Considering that the mules likely weighed about half what the draft horses weighed, such results suggest that strong mules are stronger than strong horses, pound for pound. While hybrid vigor likely gives mules more horsepower per pound than either horses or donkeys, the number of variables that affect measures of strength make this topic best suited for bar fights.
Horses are “spirited”. Donkeys are mellow, docile. Their small size makes them easier to manage than a horse.
When I brought my new mule Freckles home from Alabama, I found that several local farms feared that mules and horses wouldn’t mix. But wherever horses and mules are mixed in a pasture, they settle down to solid friendships. Horses don’t hint that they find a mule’s look odd, and mules don’t seem to mind that a horse’s ears are too short. After all, mules loved their mothers. It is the humans supervising the equids, and not the equids themselves, that have the issues.
Add one mule to your band of horses, and your band will grow by one. Mules and horses routinely form strong interspecific bonds.33
This does not mean that a mule in a herd of horses will forget who she is, or would prefer to hob nob with the horses. Researchers who studied a group of 16 mules, donkeys, and ponies found that different equids formed distinct affiliative groups.34.
Mules are famously stubborn, but a closer look leads me to think that humans are famously stubborn. We want a mule to go left. The mule wants to go right. We try to get the mule to go left. The mule tries to go right. Who, exactly, is stubborn? To us, any disobedience is stubbornness. What intimidates a horse may only anger a mule. A different management style is required if you plan to succeed with a mule.
The mule’s opinion is often right. My mule and I have been on many trail rides where I would have missed the turn, but she made it anyway, or where I tried to turn and she (correctly) chose to take another route. I ride without a bit, and don’t use a bitless bridle either. I use a halter, a roping rein, and a rein keeper, and on the trail only ask to influence at intersections. She is my smart travel companion, with good opinions, and I don’t need to do any micromanagement on the trail. Of course, when she thinks we’ve gone far enough – particularly when we are just starting our trip – the libertarian in me gives way to relentless tyranny.
When I bought Freckles, I was told how to catch her in her pasture by luring her with a bucket of grain. It has taken me a little time, but I soon realized that her initial impulse when I was heading in to catch her was to seek the safety of her little band of mares. If I kept coming after her, she kept evading me. But if I could just relax, and be more horse-like, things would change. A minute or two after getting to safety, she’d begin to relax, and a minute or two later she’d walk some yards away from them and wait for me to approach. Now I catch her on her own terms, when she is ready to be caught. And for her concession, this is sometimes less than a minute after I’ve reached the gate of her pasture. The appearance of stubbornness might be
created by our own timetables, our own aggressiveness, our own insistence in always getting our way. Horses are docile and easily intimidated. Mules need a little respect. Mule skinners are not so much mule whisperers as they are mule listeners.
Freckles doesn’t always have a strong view on which way we should go, and neither do I. Yesterday we went for a long walk through dense woods – all six feet on the ground – and we both lost the trail. I could tell that she was lost, and I could tell that she could tell that I was lost. When I made a suggestion that we try this way, she willingly acknowledged that she had no better idea. We got unlost just in time to right this article, thank goodness.
Fear the Mule?
Some folks fear mules, believing them to be good kickers. To hear the stories, a mule can touch any spot in a nearby county with any hoof, even if the farrier has her standing on three legs.
In my experience, mules are just as predictable as horses. They won’t ever injure you without warning you first. I once offered to help a woman with her stressed mule, who had been tormented for an hour in a mule clinic because he didn’t want to do what was being demanded. Remember that mules are independent thinkers, and won’t always think your idea is the best one. They were in a stand off, and judging from the woman’s behavior, the mule was winning. The clinician was growing embarrassed.
This mule was in a sweat, and was sent off with his owner to a round pen, to work it out. I offered to help. The mule felt I needed to know how he was feeling, and the next thing I knew, a front hoof was on my chest. I was amazed that he could reach so high with a front hoof, that he could move so quickly, and that he could plant a hoof with such gentleness. He could have killed me. Instead he warned me.
Half an hour later, he was doing in the round pen all of the exercises they were doing in the clinic, and that afternoon, he rejoined the group as a model citizen.
Anyone who educates a mule with a 2×4 has reason to be concerned about their welfare. Anyone who uses a twitch takes their life in their hands. Mules will remember. They’re bigger than you. They might be smarter. And they may get even. But anyone who loves their mule will be loved back. A loved mule will protect you and take care of you on the trail. You can stand behind her, casually put your feet next to hers, lie down under her, let her take a carrot slice from your lips. Don’t tempt fate on my advice, but do know that a mule can be as trustworthy as your dog – just not as foolishly obedient.
Geographic Distribution and Life Style
The anatomy of a donkey suits it for a life in harsh desert conditions and the third world, where there is little to eat and much work to do. Strong jaws and their digestive system help them get by on roadside brambles in the underdeveloped world where even their owners don’t have enough to eat. Strong hooves that grow at the rate they wear comes in handy for an animal that will never see a farrier or a vet. Studies have shown that donkeys are much more economical than humans at carrying loads or cultivating, and more economical than tractors or oxen at pulling them35. The underdeveloped world knows this.
When Central and Western Australia opened up in the 1860s, donkeys proved valuable for hauling freight through areas where horses and oxen would perish. Donkeys could endure water shortages, and did not seem to be affected by plants that were poisonous to horses. But when cars and trucks came along, the teamsters – those who drove and loved their teams of donkeys – released their teams. Five million feral donkeys now prosper in Australia, and are among the ranks of unwanted introductions, including cane toads, red foxes, feral cats, European rabbits, feral goats, and feral pigs.
Over 95% of all donkeys and mules but only 60% of all horses are found in developing countries36 – primarily in central Asia and North and East Africa. The distributions are likely a result of the distribution of surplus wealth: donkeys are used for work, horses now for pleasure, and mules for some of each.
Life in a developing country is as hard on an equine as it is on the people living there. One study assessing the welfare of working horses, mules, and donkeys found that 70% of the nearly 5,000 animals studied were thin, and over 75% of animals had limb deformities and gait abnormalities.
If you want to learn more about horses, get a mule. You won’t be able to manhandle your mule, and she will force you to move from horse whisperer to horse listener. Once you’ve learned what she’s thinking, and can coax her into sharing her day with you, you’ll be ready to return to your horse and really treat her right. But I suspect that once you and your mule have come to love each other, you won’t have an interest in going back to your horse.
If you do get a mule, be careful in your choice of veterinarian. Mules are not funny-looking horses. There are hundreds of critical differences they may need to be considered to maintain your mule’s health: including anatomic differences, respiratory differences, tolerance of medical procedures, drug metabolism, how drugs should be administered, drug response, saddling, diet37…
If you are shopping for a mule, consider your weight and that of your prospective equine. If you limit the weight on the back of the equine to 20% of its total weight, a large mule or horse might serve you better than a smaller mule. A mule will never complain about your weight, but it might not enjoy it either.
If you are interested in the vast differences in internal anatomy between donkey, mule, and horse, read Suzanne Burnham’s “Anatomical Differences of the Donkey and Mule38”. For a sideways look at the mule, read “The Famous Twenty Mule Borax Team from Death Valley California39”
1. Short, R. V. An introduction to mammalian interspecific hybrids.” Journal of Heredity 88, no. 5 (1997): 355-357.
2. Ryder, O. A., Chemnick, L. G., Bowling, A. T., & Benirschke, K. (1985). Male mule foal qualifies as the offspring of a female mule and jack donkey. Journal of Heredity, 76(5), 379-381.; Rong, R., Chandley, A. C., Song, J., McBeath, S., Tan, P. P., Bai, Q., & Speed, R. M. (1988). A fertile mule and hinny in China. Cytogenetic and Genome Research, 47(3), 134-139.; Zong, E., & Fan, G. (1989). The variety of sterility and gradual progression to fertility in hybrids of the horse and donkey. Heredity, 62(3), 393.
3. Attributed to Robert Green Ingersoll (1833-1899)
4. O’Neill, D. G., Church, D. B., McGreevy, P. D., Thomson, P. C., & Brodbelt, D. C. (2013). Longevity and mortality of owned dogs in England. The Veterinary Journal, 198(3), 638-643.
5. Spady, T. C., & Ostrander, E. A. (2008). Canine behavioral genetics: pointing out the phenotypes and herding up the genes. The American Journal of Human Genetics, 82(1), 10-18.
6. There are many good stories about mule skinners and mules in Death Valley. Here’s a short one: “Twenty Mule Teams”. Death Valley National Park. https://www.nps.gov/deva/learn/historyculture/twenty-mule-teams.htm
7. Clutton-Brock, Juliet. Horse power: a history of the horse and the donkey in human societies. Natural History Museum Publications, 1992.
8. Proops, Leanne, Faith Burden, and Britta Osthaus. “Mule cognition: a case of hybrid vigour?.” Animal cognition 12, no. 1 (2009): 75-84.
9. Osthaus, B., Proops, L., Hocking, I., & Burden, F. (2013). Spatial cognition and perseveration by horses, donkeys and mules in a simple A-not-B detour task. Animal cognition, 16(2), 301-305.
10. The source of this quote is http://scienceblogs.com/cortex/2008/07/31/mules-are-smarter/, but I don’t know what study they are citing.
11. A good photo comparing horse and donkey skulls may be found here: http://www.ivis.org/proceedings/AAEP/2002/910102000102.PDF
12. Purdy, Stephen R. “A Donkey is Not a Horse: The Differences from a Practical Veterinary Standpoint.” https://www.vasci.umass.edu/sites/vasci/files/donkeynotahorse.pdf
13. Mueller, P. J., P. Protos, K. A. Houpt, and P. J. Van Soest. “Chewing behaviour in the domestic donkey (Equus asinus) fed fibrous forage.” Applied Animal Behaviour Science 60, no. 2
14. Purdy, Stephen. op.cit.
15. Preston, Lisa “The ultimate guide to horse feed, supplements and nutrition” Skyhorse Publishing, 2016.
16. Chandley, AC “Why do not the mule and hinny look alike ?.” The Mule (Quarterly Journal of the British Mule Society) 43 (1989): 7-10.
17. I am not alone in this thinking. One internet author writes “Where each mule places each foot is critical. He does it from memory. The mule cannot see his feet, but he anticipates where each foot has to go as he moves forward. Horses do the same, but the mule is much better at it.” – http://saitosdojo.com/whymul.htm
18. Robinson, Betty. “Mules and the Grand Canyon.” in Hauer, John (ed.) The Natural Superiority of Mules. The Lyons Press. 2005. p. 49.
19. Grand Canyon National Park “Woman injured in mule accident in Grand Canyon National Park”. May 5, 2009. https://www.nps.gov/grca/learn/news/mule-accident.htm
20. Metcalfe, John. “Mapping the Grand Canyon’s Gruesome Legacy of Death”. CityLab. May 16, 2015. https://www.citylab.com/environment/2015/05/mapping-the-grand-canyons-gruesome-legacy-of-death/394040/
21. There are many mansplainers out there who think that mule skinning is the business of taking the skin off a mule with a whip. Today, at least, mule skinners could not earn a living by doing this, and out smarting a mule seems a more likely way to receive a pay check. The term muleskinner is the same as “mule skinner” and “mule-skinner”. Use whatever spelling appears in local use. Or swap in the term “muleteer”. Or “mule whisperer”.
22. See https://www.horsesandpeople.com.au/search/node/The%20Equine%20Pain%20Face
23. Ashley, F. H., A. E. Waterman-Pearson, and H. R. Whay. “Behavioural assessment of pain in horses and donkeys: application to clinical practice and future studies.” Equine veterinary
journal 37, no. 6 (2005): 565-575.
24. Seyoum, A., Birhan, G., & Tesfaye, T. (2015). Prevalence of Work Related Wound and Associated Risk Factors in Cart Mules of Adet Town, North-Western Ethiopia. American-Eurasian Journal of Scientific Research, 10(5), 264-271.
25. Burnham, Suzanne L “Anatomical differences of the donkey and mule.” In Proceedings, vol. 48, pp. 102-109. 2002.
26. Yousef, M. K. “The burro: a new backyard pet? Its physiology and survival.” Calif Vet 33 (1979): 31-34.
27. Stephen, J. O., Baptiste, K. E., & Townsend, H. G. (2000). Clinical and pathologic findings in donkeys with hypothermia: 10 cases (1988–1998). Journal of the American veterinary medical
association, 216(5), 725-729.
28. One authority, in a section entitled “Mules can stand the heat and cold better than the horse”, devotes a a couple paragraphs to discussing the better heat tolerance of the mule, but in her only reference to cold tolerance, writes “The reason for their exceptional cold tolerance is yet to be understood.” Attar, C. (2009). The Mule Companion: A Guide to Understanding the Mule. CCB Publishing. p. 91.
29. Stephen, Jennifer O., Keith E. Baptiste, and Hugh GG Townsend. “Clinical and pathologic findings in donkeys with hypothermia: 10 cases (1988–1998).” Journal of the American veterinary
medical association 216, no. 5 (2000): 725-729.
30. Osthaus, Britta, Leanne Proops, Sarah Long, Nikki Bell, Kristin Hayday, and Faith Burden. “Hair coat properties of donkeys, mules and horses in a temperate climate.” Equine veterinary
31. Yilmaz, O., Boztepe, S., & Ertugrul, M. (2012). The domesticated donkey: III. Economic importance, uncommon usages, reproduction traits, genetics, nutrition and health care. Can J App Sci, 3(2), 320-338.
32. See http://leahaven.blogspot.com/2010/08/labor-day-at-leahaven.html
33 . Budiansky, S. (1997). The Nature of Horses: Their Evolution. Intelligence and Behaviour, Phoenix.; Jensen, P. (2006). Domestication—from behaviour to genes and back again. Applied
animal behaviour science, 97(1), 3-15.
34. Proops, L., Burden, F., & Osthaus, B. (2012). Social relations in a mixed group of mules, ponies and donkeys reflect differences in equid type. Behavioural processes, 90(3), 337-342.
35 . Yilmaz, O., Boztepe, S., & Ertugrul, M. (2012). op.cit.
36. Fielding, D., 1991. The number and distribution of equines in the world. In: Proceedings of the Colloquium on Donkeys, Mules and Horses in Tropical Agricultural Development, Edinburgh, 3–6 September, pp. 62–66.
37. Purdy, Stephen. op.cit.
38 . Burnham, Suzanne L. op.cit. Available as a PDF here: http://www.ivis.org/proceedings/AAEP/2002/910102000102.PDF
39. There are a number of publications, new and old, about the Death Valley mules. This citation is to a reprint of “The Famous Twenty Mule Borax Team from Death Valley California” produced by the Pacific Coast Borax Co. in 1900. It is available on Amazon.