Animals Pets 12 Astonishing Facts About Horses By Jaymi Heimbuch Writer California Polytechnic State University, San Luis Obispo Jaymi Heimbuch is a writer and photographer specializing in wildlife conservation. She is the author of The Ethiopian Wolf: Hope at the Edge of Extinction. our editorial process Twitter Twitter Jaymi Heimbuch Updated May 31, 2017 Share Twitter Pinterest Email Animals Wildlife Pets Animal Rights Endangered Species Horses have a weird side Photo: canadastock/Shutterstock Horses have been around for around 50 million years, and in that time they've had a chance to develop some really interesting quirks and features to their anatomy. Horses began their history in North America, and spread into Asia and Europe using the land bridge. While they died out in North America, they continued to thrive in eastern Europe and central Asia, continuing to evolve to their new landscape. The species has been domesticated for the last 6,000 years and that, too, has been plenty of time for human influence to play some pretty interesting tricks on horses. Since domesticating the horse, humans have created some 400 different breeds, used for purposes from racing to war, from plowing to pulling carts and carriages. Our own human history has been greatly shaped by our partnership with the horse, and the horse has of course been shaped significantly by us. But many of the odd features of the horse developed well before we had a hand in their evolution. Alongside photos of gorgeous and oddball horses, you'll learn about the more fascinating features of the species that we all know and love. The eyes have it Photo: VICUSCHKA/Shutterstock Horses have some of the largest eyes of any land mammal (the moose takes the trophy), with a diameter of about 2 inches. Like many prey species, horses' eyes are located on the side of their head so they have a wide range of vision — they can see nearly 360 degrees, and have blind spots only immediately in front and immediately behind their bodies. Horses mostly use monocular vision, meaning both eyes are used separately. So a horse can see and process different things happening on different sides of her body. However, a horse also uses binocular vision when looking ahead, so she can focus both eyes on a single object in front of her. A horse will raise her head to increase her field of binocular vision and get a better focus on things in the distance. A horse can't use monocular vision and binocular vision at the same time, but rather switches the type of vision she is using by changing the position of her head to face the object. Horses can do a lot with their eyes. But there's something they can't do with their gut. Continue to the next slide to find out what! Horses can't vomit Photo: Sari ONeal/Shutterstock It is physically impossible for horses to throw up. This mechanism is vital to survival in so many other species, including humans. The ability to get rid of whatever toxic substance is upsetting your stomach, or whatever meal is weighing you down when trying to evade a predator, can save your life. So what keeps horses from having this ability? According to veterinarian Joe Bertone in an article in Equus, "[T]he muscles of the equine lower esophageal sphincter are much stronger than in other animals, making it nearly impossible to open that valve under backward pressure from the stomach. Also, the equine esophagus joins the stomach at a much lower angle than in many animals, so when the stomach is distended, as with gas, it presses against the valve in such a way that holds it even more tightly closed. And, located deep within the rib cage, the equine stomach cannot be readily squeezed by the abdominal muscles. Finally, horses have a weak vomiting reflex---in other words, the neural pathways that control that activity in other animals are poorly developed in horses, if they exist at all." That's the "how" for the inability to vomit. The "why" is a little more vague. Whereas humans and nearly every other vertebrate can vomit, the horse (and most rodents and rabbits) can't. The evolutionary reason for this inability in horses isn't known for sure, though one theory is that it is so they won't vomit when running at a full gallop from a predator, since the back-and-forth motion of their body could induce vomiting. The horse's closest relative is the rhino Photo: Sari ONeal/Shutterstock There is only one surviving branch of the horse family, and that is Equus. This branch includes not only Equus caballus, the domesticated horse, but also the Przewalski's horse, zebras, asses and donkeys. But there are a couple other surprising relatives to the horse — species that few of our domestic horses have probably ever seen. According to the American Museum of Natural History, "Horses belong to a group of mammals with an odd number of toes... Most members of this group, known as perissodactyls, are extinct. But several species survive at present. They include rhinoceroses and tapirs, the horse's closest living relatives. Horses are more closely related to extinct perissodactyls...than they are to cows, pigs, and goats." In other words, though horses spend the most time around cows, pigs and goats on a farm, they share a much closer kinship to the more relatively exotic rhinos and tapirs. Arabian horses aren't built like the others Photo: Olga_i/Shutterstock This breed is famous for its grace, speed and endurance. Arabians are thought to be one of the oldest breeds of domesticated horse, and were critical to the culture and lives of desert tribes in the Middle East. Classic books including "The Black Stallion" and "King of the Wind" feature the ancient and storied breed. However, Arabian horses stand out not just for their long history and particularly good looks. Arabian horses are built differently than other horses. Arabians have a greater bone density than other horses, and also a shorter back with one fewer lumbar vertebrae. Additionally, Arabians have one fewer pair of ribs, and their ribs are set wider. And of course Arabians are known for carrying their tail high, almost like a flag behind them. That might be as much about having two fewer tail vertebrae than other horse breeds as it does with being high-spirited. Ponies, miniature horses are only sort of the same Photo: Rita Kochmarjova/Shutterstock Horse, pony... miniature horse? What's the difference? You probably know that both ponies and miniature horses are smaller versions of the typical domestic horse, but what makes the two different from each other? Well, miniature horses are ponies, but ponies aren't miniature horses. It gets a little confusing and controversial in the horse world. But here's the basic run down: Any horse that is shorter than 14.2 hands, or 58 inches tall at the withers, is considered a pony. Miniature horses are usually 34–38 inches tall, which puts them squarely in the pony category. However, miniature horses are considered by many enthusiasts to be a distinct breed of horse — like the Falabella, for instance — and one that keeps more of the horse body type and proportions. On the other hand, ponies have shorter legs, longer bodies and an overall stockier build than horses. The Shetland pony, Icelandic pony and Dartmoor pony are all examples of the typical pony build. So can you call a miniature horse a pony? Yes, to some people anyway. There will likely be miniature horse registry officials giving you the side-eye if you do, but technically you're correct. But you can't call any pony a miniature horse, because there are breed factors that come into play in miniature horses. Let's get back to something a bit less nebulous: teeth! Click through to find out why different horses have a different number of teeth. Teeth tell the truth Photo: Horse Crazy/Shutterstock There's a lot of crazy stuff to know about horse teeth. There's so much more to it than the whole, "Don't look a gift horse in the mouth" saying (which we'll explain). For starters, male and female horses have a different number of teeth. Males have 44, while females have 36-40 — if they each have a complete set, that is. So, if you're ever looking at just a horse skull, you may be able to tell if the skull came from a male or female by counting the teeth. Those extra teeth in males come in the form of canine teeth, found between the incisors and the cheek teeth. There are two on top and two on bottom. These are also known as fighting teeth, since males fight and bite one another to be the leader of a herd of mares. Horses can also sometimes have what are called "wolf teeth" which are pre-molars that sometimes erupt through the gums. However these are often pulled for health and for comfort when wearing a bit. Think of them as sort of the horse version of wisdom teeth. You can age a horse, somewhat anyway, by the length of their teeth. Horses need to be able to chew and grind up grasses and plants their entire lives to survive, so they have teeth that continue to erupt from the gums for much of their lives. University of Missouri notes, "The art of determining the age of horses by inspection of the teeth is an old one. It can be developed to a considerable degree of accuracy in determining the age of young horses. The probability of error increases as age advances and becomes a guess after the horse reaches 10 to 14 years of age. Stabled animals tend to appear younger than they are, whereas those grazing sandy areas, such as range horses, appear relatively old because of wear on the teeth." And the "gift horse" saying? It comes from when horses were a more common part of life for everyone. If you're given a horse, it would be rude to inspect its teeth to learn more about its age and health. Instead, you just accept the gift for what it is. But as we know now, there's a whole lot to discover about a horse based just on its teeth! The only real wild horses left aren't mustangs Photo: loflo69/Shutterstock There are quite a few horses around the world that are called wild. Mustangs of the American west are perhaps some of the most famous. However, the horses we call wild, from the mustangs to the Exmoor ponies to the "wild" horses of the Camargue marshes are technically all feral horses. They are descendants of domesticated horses that have been living on their own and reproducing for decades, or even centuries, without significant influence from people. So are there any truly wild horses left? Surprisingly, yes. There is one single sub-species of horse that is still entirely wild, having never been domesticated by humans. The endangered Przewalski's horse is native to the steppes of Mongolia. We highlighted this horse recently, noting, "The Przewalski's horse is a subspecies of Equus ferus and is considered the closest relative of the domestic horse. It is cousin to zebras and the wild ass, which all fall under the Equidae family. The split between Przewalski's horse species and the ancestors of domestic horses happened somewhere between 120,000 and 240,000 years ago." The Przewalski's horse had a narrow brush with extinction and is still on the cusp of disappearing forever. It would be a tragedy to lose the last of these horses, since they are a link back in time to horses before domestication. Many-muscled ears help horses hear Photo: mariait/Shutterstock A horse can shift its ear to facing forward to facing backward, and that kind of movement requires a lot of muscles. According to Ashley Griffin, MS, University of Kentucky, "Horses' ears can move 180 degrees using 10 different muscles (compared to three muscles for the human ear) and are able to single out a specific area to listen to. This allows the horse to orient itself toward the sounds to be able to determine what is making the noise." What's interesting is that not only do horses use their twitchy ears to pinpoint sound, but they also use them to communicate. Most people know that a horse with his ears pinned back is indicating anger, but there's a lot more discussed during ear movement. The Washington Post reports on a recent study in Current Biology. "Study author Jennifer Wathan, an associate professor of psychology at the University of Sussex, took life-size photos of horses whose attention was attention focused on something. She then placed the photos between two feed buckets in front of real horses. The horses were able to tell which bucket the ersatz horse was looking at, and chose to direct their attention to it, as well." So all their muscles in a horse's ears are for more than just directional listening, but also for sending a variety of messages to other horses. That horse isn't laughing Photo: Rita Kochmarjova/Shutterstock When a horse curls his upper lip and raises his head in the air, many people think this is little more than a funny expression. When the behavior is shown on television shows or in movies, it is often used to say the horse is laughing. But this is no laughing matter. The behavior is called the flehmen response and it's all about getting a better whiff of an interesting smell. Kentucky Equine Research Inc. reports, "Sharon Crowell-Davis, DVM, PhD, Dipl. ACVB explains that horses display the flehmen response to facilitate transfer of inhaled scent molecules (pheromones and possibly some other substances) into the vomeronasal organ (VNO), a specialized chemosensory structure found in many mammals. Once known as Jacobson's organ, the VNO has different physical forms and locations in various species of animals. In general, it is connected with the mouth, nasal passages, or both. When certain scents impact the VNO, signals are transmitted to centers in the brain's accessory olfactory bulbs. Depending on the scent detected, various physiologic and behavioral reactions may then be triggered." In horses, that is a curled upper lip at the end of a stretched-out neck. Stallions show the flehmen response most often as they pick up the pheromones of mares. Mares will flehmen shortly after birth as a response to the pheromones of their newly born foal. All horses can flehmen, and it's just a matter of wanting to learn more about a particular scent — sometimes it happens as a response to coming a cross a brand new, or particularly strong scent. It may look like a horse's smile but it's all about a horse's smell. This breed of horse has a metallic coat Photo: Olga_i/Shutterstock The Akhal-Teke horse is particularly famous for its coat. This "supermodel" of the horse world was listed in our 10 strange and beautiful horse breeds article. While many well-tended horses have a beautiful sheen on their coat, this breed takes it to a new level by boasting a metallic shine. It is particularly apparent on the buckskin, palomino, cremello and perlino coat colors. Akhal-Teke.org explains why the shimmering effect of the coat happens: "This is caused by the structure of the hair; the opaque core is reduced in size and in some areas may be absent altogether. The transparent part of the hair (the medulla) takes up this space, and acts like a light-pipe, bending light through one side of the hair and refracting it out the other side, often with a golden cast." The lanky, athletic breed began in Turkmenistan, perhaps as far back as 3,000 years. However, the breed suffered a significant decline in modern history when the Soviet Union ordered horses to be slaughtered for meat, and the breed hit a low of only 1,250 horses. Now there are some health issues that arise due to a lack of genetic diversity. This includes, sadly and ironically, a fatal disease called Hairless Foal Syndrome in which a foal is born without a coat, mane or tail, along with other significant health problems. Horses are smarter than we realize Photo: Lenkadan/Shutterstock Many people that think horses are not the brightest crayon in the box, that they are simple-minded animals without much in the way of intelligence. But researchers are proving this widespread notion wrong. A 2010 study by Carol Sankey of the University of Rennes and colleagues revealed more about the horse's memory and intelligence than we previously thought. With 23 horses in their study, the scientists tested the horses' response to positive reinforcement by a trainer. A female trainer worked with the horses on 41 different actions. The researchers found that horses getting positive reinforcement picked up training faster and had fewer "bad" behaviors than other horses. What's more, even after spending eight months apart, the horses would gravitate toward that original trainer, remembering the positive association with the specific person. Another study by Jessica Lampe, James Madison University psychology alumni, found that horses use input from several of their senses to identify familiar and unfamiliar people. "During these tests," reports James Madison University, "Lampe examined differences in horse behavior during 'congruent' and 'non-congruent conditions.' When there is congruency, the voice, smell, image, taste, and sound of a person matched, while during non-congruency, one of these senses was not consistent. Lampe found that horses were more interested in instances of non-congruency... Like humans, they looked at interesting stimuli longer. The results showed that horses integrate information they receive from all of their senses to recognize individuals." Meanwhile, Evelyn Hanggi of the Equine Research Foundation in Aptos, California has proven a long-standing assumption about horse intelligence wrong. Horse and Rider reports, "The long-held theory is that horses lack interocular transfer -- they can't transfer information from one side of the brain to the other. But Hanggi has proven differently. 'We found that horses had no trouble recognizing objects with one eye that they had previously only learned about with the other (interocular transfer),' Hanggi says... Their ongoing research continues to redefine how horses learn." The notion of horses as unintelligent beasts of burden is long being continually eroded by research, and we are finding that this species is far more clever than often assumed. Mules and hinnies Photo: Papa Bravo/Shutterstock A mule is a hybrid between a male donkey (jack) and a female horse (mare). They've long been a desirable hybrid because they're considered to have some of the best physical characteristics and personality traits from both species. They have the size, strength, sure-footedness, patience, intelligence and an overall good nature that make them great working animals. Mules are typically infertile; however, a molly mule is a female mule that has an estrus cycle and so can technically reproduce. It is very rare for a molly mule to become pregnant, but it sometimes happens. On the other hand, there hasn't been a single fertile male mule in the record books. So even if a molly mule does get pregnant with a foal, it wouldn't be by a male mule. Her offspring is sired either by a jack or a stallion. But there's another type of hybrid you may be less familiar with: a hinny. This is the offspring of a female donkey (jenny) and a stallion. Hinnies are often smaller than mules, primarily because the donkey mother is smaller than a mare and thus the growth potential of her foal in the womb is limited. Like mules, hinnies are infertile. Though female hinnies can sometimes have an estrus cycle, there has only been one case of a female hinny producing an offsping. Other hybrids in the horse family branch include a zeedonk or zonky, which is a zebra crossed with a donkey; a zorse, which is a zebra crossed with a horse; a zony, which is a zebra crossed with a pony; and even more specifically, a zetland, which is a zebra crossed with a Shetland pony.