Your Horse's Limbs: Does Form Follow Function?

No hoof, no horse is a time-tested adage. So, too, is the advice -- given in countless books, articles, and videos -- to scrutinize a horse's conformation carefully before you buy. No doubt you've seen the photos and illustrations of "good" and "bad" conformation, and you've studied them carefully and tried to measure prospective mounts against the ideal.

But just what constitutes "ideal?" To some people, ideal might mean "prettiest" or "most pleasing to the eye." To others, it might mean "best suited to my chosen discipline," regardless of how it looks. To still others, it might mean "most likely to remain sound" or a combination of all three.

As anyone who has ever bought a young horse as a "prospect" can attest, at times there seems to be no relationship among so-called good conformation, performance success, and career longevity. Many is the sales-topper at the fancy Thoroughbred yearling sale which has gone on to accomplish zilch on the track, and the in-hand sport-horse champion two- or three-year-old which never makes a victory gallop in the jumping or dressage arena. Yet yearlings still bring big money at the sales, and the popularity of sport-horse breeding classes continues to increase.

We asked several leading experts for their take on the conformation-performance-soundness issue. We were surprised to learn that, despite the abundance of conventional wisdom in this area, the effects of conformation -- in particular, limb conformation -- on soundness and performance have received little scientific study. We asked our experts to share what they've learned in their years of treating and "vetting" horses. What they had to say might surprise you.

A Look At Limb Structure

In "Understanding Leg Conformation" (Back To Basics, July 1999), The Horse gave you an overview of the equine skeletal limb structures and introduced you to the leg bones, their functions, and what are commonly considered conformational limb defects. Let's review some of the key concepts here from a biomechanical perspective.

A horse's front legs serve quite a different purpose than do his hind legs, says Bill Moyer, DVM, head of the Department of Large Animal Medicine and Surgery at Texas A&M University's College of Veterinary Medicine in College Station. The powerful hindquarter muscles are the horse's "engine," generating energy as their fibers contract and release. The hind limbs provide that energy, and their angled structures -- hips, stifles, hocks, and fetlocks -- allow the joints to close and open to provide propulsion. The front legs are "more of a prop," says Moyer. "They have some propulsive capability, but their function is more that of steering and support." The front legs support the weight of the head and neck, creating a sort of "cantilever effect," according to Moyer, with the head and neck projecting from a vertical support (the front legs) and a degree of tension required to hold the projection in place. Thus burdened, the front legs support 60% to 65% of the horse's weight -- meaning that all horses, in effect, are naturally "on the forehand."

The more angular hind limbs have a "mechanical advantage" in terms of their ability to produce power and speed, says Moyer. The angles (joints) can close or "fold" on impact, absorbing shock; then deliver energy as they open during the next phase of the gait to propel the horse forward. A limb's ability to close is essential in order to prevent injury to the joints, he adds. Imagine the pain you would feel -- and the damage you would inflict to your knees and ankles -- if you jumped off a wall and landed with your legs straight and rigid instead of flexed and relaxed. This flexing allows the ligaments and tendons that support the joints to absorb a good deal of the shock; without the flexion, the bones and cartilage themselves take the brunt of the pounding.

The Form-To-Function Issue: Pretty Is As Pretty Does?

Most equine breed registries maintain certain conformational standards. Some standards, such as for the profile of the head, vary considerably from breed to breed and might be equal parts aesthetic and utility. Others, like general standards of "harmony of parts," might remain fairly uniform, whether the equine in question is a Shetland pony or a Shire. Still, horse people tend to emphasize different builds and attributes, depending on the sport or use for which the horse is intended.

We use overall conformation as a general indicator of suitability for our intended discipline, and many of us have been taught that limb structure plays an important role in athletic ability. In other words, we think of conformation as an indicator of performance potential. But is it?

Harry Werner, VMD, whose North Granby, Conn., private practice specializes in sport-horse lameness and prepurchase exams and who has spoken on the subject of lameness to the American Association of Equine Practitioners, says that he does consider conformation in terms of intended use when he conducts a prepurchase exam. He adds, however, that "looking at conformation and attempting to predict performance success are more of an art than a science that can be learned in a class or out of a textbook." (He modestly claims not to have mastered the art.)

"Much has been written, but little has been proven about the relationship of conformation to performance," adds Werner. That might be changing, he says, thanks to the application of technology to the studies of equine biomechanics and gait analysis. Researchers today are using videotape, force plates (which measure the manner and force with which hooves strike the ground), and other methods to conduct scientific analyses of gait and movement. Werner and other experts hope that such studies will show valid links between conformational attributes and performance characteristics, and offer new insights into age-old soundness problems.

Research already has disproven a few pieces of conventional wisdom, Werner says. "For years it was accepted that a long toe, especially when it was attached to a long, sloping pastern, increased stride length," he offers by way of example. "In racehorses, long toes were desirable, the thinking being that a longer stride would translate into more speed. Gait analysis has since suggested that it doesn't actually work that way -- stride length, in fact, does not appear to correlate with the way in which the hoof is trimmed."

Equine researchers are learning more about biomechanics and performance, but they've learned far less than what is known about human athletes, says Moyer. "There is a correlation between very bad conformation and injury, but I'm not sure there's a correlation between conformation and ability to excel in certain disciplines."

Moyer points out that "various phenotypes (physical types) have been identified in humans. For instance, we know that the successful male marathoner is likely to be 5'9" or shorter, less than 140 pounds, and leggy. The hundred-meter sprinter probably has huge thighs and is "bulked up" for the explosive action and power his sport requires. The offensive tackle in football is physically the opposite of the marathoner: usually at least 6'4" or 6'5" and weighing more than 300 pounds.

"Gross measures exist in the horse world, but they haven't been studied and refined as thoroughly as human phenotypes," Moyer continues. "We know that not many Quarter Horses could run the Belmont Stakes at a mile and a half. Why? Because most Quarter Horses are the football running-back phenotype, built low to the ground and for explosive power and speed over a quarter of a mile. The Thoroughbred, on the other hand, tends to be more 'greyhound-y,' like the marathoner, with a leaner build that favors stamina over sprinting ability."

Moyer goes so far as to dispute the very notion of "ideal" conformation. "Who described the ideal to begin with?" he asks. "What scientific evidence is there to support the accuracy of these ideals?" He points out that the very concept of "ideal" is itself subjective. "Ideal" to one expert could mean "able to win the Triple Crown" (or an Olympic gold medal). To another, "ideal" could mean "able to remain sound and serviceable for a long period of time."

In judging conformation with regard to performance, Moyer says, most people fall into the trap of "what I look for is only as good as my memory. If I'm looking for a racehorse, I remember what Secretariat looked like; so that's what I like to see. Unfortunately, that might be a totally false premise. I could also use as my standard the fact that the Standardbred harness racing champion Rambling Willie was the plainest-looking thing you've ever seen, yet he raced until the unheard-of age of 14. Rambling Willie's conformation was not what you would call ideal. Does that mean all racehorses should look like him? Of course not."

Gayle Trotter, DVM, MS, Dipl. ACVS, a professor of clinical sciences at Colorado State University's College of Veterinary Medicine and Biomedical Sciences in Fort Collins, holds a moderate viewpoint on the subject. He agrees with Werner and Moyer in that don't think there is an ideal equine conformation," but he says he recognizes the fact that "purported ideals for the various breeds were developed by individuals who have observed those breeds doing what they're supposed to do." In other words, excellence in performance gave rise to the establishment of physical attributes as desirable in achieving that performance.

He, too, believes that "evaluating conformation is always going to be a bit of an art form." He says that the limbs are the most important aspects of a horse's conformation ("all that mass that sits above them gets transmitted down to the limbs," he explains), but adds that he critiques the horse as a whole when he's assessing build and suitability.

"Does the horse look balanced? Do his parts look as if they go together? I look at the way his limbs move and the quality of his gait. Stiff, stilted action, which may or may not result from ‘post-legged,' upright conformation, generally is not good in terms of athleticism."

Can Conformation Predict Soundness?

Athletic performance is just part of the equine-suitability equation. The other part is the horse's ability to withstand the athletic demands placed on him. Most people don't want to buy an unsound horse, nor do they want to buy a horse which they believe is likely to become unsound. Again, conformation traditionally has been viewed as an indicator of the potential of such possibilities. Although our experts deny that the odds of a horse's staying sound or going lame can be predicted by his conformation, they pointed to many of the same faults as red flags -- conditions that, in their experience, are associated with a greater frequency of soundness problems. We'll look at each defect and explain why it might predispose a horse to physical difficulties, with the caveat that every veterinarian knows of horses whose conformation is a textbook example of terrible, yet who have led sound and productive lives.

Straight hind legs. Moyer, Trotter, and Werner agree that a hind limb whose angles exceed the normal range (and that range, they admit, is difficult to hang specific numbers on) might be more susceptible to certain unsoundnesses. A straight hind leg usually incorporates a straight stifle, says Trotter, and a straight stifle might be prone to upward fixation of the patella ("stifle lock"), a condition that occurs when the ligament inadvertently hooks over the bottom of the femur, causing the leg to straighten and lock in place, much as it does when the horse goes to sleep standing up.

A straight limb's reduced ability to flex also might render it more subject to concussion-related injuries and unsoundnesses, adds Werner. Excessively straight (as viewed from the side) front or hind limbs "can't absorb impacts well" and might be prone to degenerative joint disease (DJD) or other conditions.

Excessively angled limbs. Too much angle apparently can be as bad as not enough. As Werner explains it, a limb's supporting structures (the suspensory ligaments and digital flexor tendons) have a certain normal range of motion and degree of elasticity and "memory." If the limb is forced to flex beyond its normal range of motion, the suspensory apparatus might be stretched too far and sustain damage. Horses which regularly place great strain on their joints, such as racehorses and jumpers, are at above-average risk levels for such injuries in the first place; if those horses also have long, steeply angled pasterns, they might be at even greater risk.

Are excessively angled hocks (sickle hocks) as bad as too-straight ones? Trotter says he's observed a relationship between sickle hocks in yearlings and the development of juvenile bone spavin (arthritis), and believes that the correlation might be due to the "terrible compressive forces on the bones at the front of the hock" caused by the angularity. Werner, however, says, "I don't like to see horses that are overly sickle-hocked, but I'd rather see that than a very straight hock." As for Moyer, "I've seen sore hocks in every shape and size horse you could imagine: sickle-hocked, cow-hocked, straight, and pleasing. I've seen racehorses, barrel horses, Shetland ponies, and pasture ornaments alike with arthritic hocks -- and the same is true, by the way, with navicular disease."

Misaligned front legs. Our experts agree that they like to see front legs in which the forearm, knee, and cannon bone are in alignment. Faults such as being "back in the knee" or "calf-kneed" (in which the knee is set slightly behind the line of the forearm and the cannon bone, as viewed from the side) or "bench-kneed" (in which the cannon bone is set slightly to the outside of the knee, as viewed from the front) produce unequal loading on the bones, joints, and supporting structures and might lead to bone chips or other unsoundnesses. (These faults can be compared to an imperfectly mounted tire on a racecar, says Moyer; the misalignment produces a sort of "wobble" and a load imbalance that eventually will affect the related structures.) "Over at the knees," the opposite of calf knees, also is a fault, but seems less likely to lead to problems, says Werner.

Small or poorly shaped feet. As Werner puts it, "I can't remember the last time I saw a horse whose feet were too big; but on a daily basis I see horses with problems, such as chronic heel lameness, caused by too-small feet." Hoof shape itself is important, says Moyer, who notes that he's seen more cases of sole and heel bruising and of navicular syndrome in horses with long toes, low heels, and flat soles.

Conformation Implications

Werner acknowledges that gross conformational defects might indeed be the "seeds of disease." "The trick as a practitioner, he says, is to judge whether a fault is significant enough to warrant notifying the buyer who has hired him to conduct a prepurchase exam. "When does a cow-hocked horse become a clinically significant cow-hocked horse?" he asks by way of example. In his own practice, he says, he evaluates conformation in terms of "ranges of normals" and tells his clients that "every conformational fault fits into a whole horse; you have to consider the whole picture."

That picture, of course, includes evaluating the horse in motion as well as "stood up" for inspection, say our experts, all of whom have seen examples of horses with terrible-looking legs who moved with grace and elegance, and animals with textbook-perfect limbs whose movement rivaled an eggbeater's for awkwardness and inefficiency. When he conducts a prepurchase exam, Trotter pays particular attention to the way in which the feet land. If the foot does not land flat, he says, the limb structures might be subjected to unequal concussive forces that might lead to unsoundness.

Our experts agree on one final piece of advice: Before you buy a horse, bone up on conformation and learn what's generally considered "normal" or "ideal" for your breed or discipline. Have a reputable veterinarian who's experienced in evaluating and treating that breed or type of horse conduct a prepurchase exam. Get a knowledgeable horseman -- your instructor might be ideal -- who's associated with neither buyer nor seller to evaluate the horse's suitability. Keep in mind that "it's not the vet's job to predict how well or poorly any given horse will suit your intended use," as Werner puts it. "His job is to give you information so that you can make an informed decision about the horse's suitability." If, as our experts hope, researchers continue to study gaits and movement -- and especially if some future study focuses on the long-term effects of conformation on performance and soundness -- veterinarians and buyers alike will be that much better informed.

About the Author

Jennifer O. Bryant

Jennifer O. Bryant is editor-at-large of the U.S. Dressage Federation's magazine, USDF Connection. An independent writer and editor, Bryant contributes to many equestrian publications, has edited numerous books, and authored Olympic Equestrian. More information about Jennifer can be found on her site,

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