Variations in Horse Conformation
Thanks to a cornucopia of breeds and disciplines, there is no one ideal equine body type; there are, however, conformation traits that can affect performance.
In architecture, form follows function. But in horsemanship, the reverse generally proves true. Horses come in many shapes and sizes, yet the basic form is remarkably consistent across the species. The relationships within that form, however—the characteristics of various body parts and how they interconnect and work together—can impact and even drive function. Studies of equine conformation often focus on the limbs. However, the proportions of and relationships between the horse’s upper body and its parts can also impact his health and success in a given discipline.
In this article we will identify some conformation deviations in a horse’s upper body that might affect performance.
From Muzzle to Tail
A horse has a relatively small head in proportion to his body, and breeder/owner preferences for head shape and size vary from breed to breed. Compare the refined, dished face desirable in Arabians, for instance, with the wide jowl and straight profile characteristic of Quarter Horses. Less-than-ideal head conformation generally doesn’t cause problems—it just impacts the animal’s aesthetic appeal—but severe deviations from normal in the mouth can present physiological issues. Because horses’ teeth wear and erupt more or less continuously throughout life, how those teeth meet can impact overall dental health and forage consumption. For instance, without intervention, “parrot mouth” (overbite) in foals can worsen as the horse matures, influencing tooth growth and how the cheek teeth wear against each other. Veterinarians can correct this congenital (present from birth) flaw by preventing the upper teeth from outpacing the growth of the lower teeth or, in serious cases, surgically.
Moving toward the horse’s trunk, obvious defects, such as ewe neck (concave over the topline), wry neck (torticollis, or neck twisting), or muscle loss and wasting, can impair the horse’s performance ability or, in severe cases, even his capacity to complete maintenance behaviors such as grazing. More subtle variations in neck length and muscling might impact success at different disciplines. For example, Marvin Beeman, DVM, a Colorado equine practitioner who lectures extensively on conformation, says one ancient Greek writer described horses such as Alexander the Great’s famed Bucephalus as having relatively short, muscular, upright necks. “The reason for this breeding,” says Beeman, “was said to keep necks above foot soldiers … (so horses could) use their chests to knock soldiers around. Those horses didn’t jump and cut cattle.” But for today’s equine sports, Beeman says longer-necked horses typically have an advantage.
Prominent withers likely won’t affect gait negatively or increase injury risk, but they can impact saddle fit and should be considered when choosing tack to prevent rubs and soreness. Flat, mutton withers, on the other hand, will not hold a saddle in place, and owners must call in reinforcements such as breastplates and cruppers.
Length and slope of a horse’s shoulder will influence his gait. Beeman points out that the sloping shoulder characteristic of Morgans and Arabians lends itself to flashy movement, while the more upright shoulder of the Thoroughbred is designed for speed. A straight shoulder combined with a short, upright pastern, however, can increase concussion to the limb and shorten the stride, potentially increasing risk of suffering from muscle fatigue and/or sustaining an injury.
The biomechanics of the equine spine is a fairly new research field, but in a 2010 study Van Weeren et al. found that “… the biomechanics of the lumbosacral region (the loin, between the lumbar vertebrae and the sacrum) region may vary considerably depending on underlying anatomical variations, particularly associated with the dorsal spinous processes in the lumbosacral junction.
“The combination of anatomical variation and altered force generation by the mutifidi (muscle complexes, in this case over the back) may result in altered motion at the lumbosacral junction and potentially have an impact on performance or the risk for pathology and the development of back pain,” continue the authors. Or, simply, the muscling along the back can influence spinal joint movement and, thus, that horse’s risk of back injury.
Different Traits and Types
Through generations of genetic selection, horses have developed a wide array of physical characteristics. Thus, we can’t apply the same conformational ideals for a Clydesdale to a Paso Fino. Even among light horses, traits vary—anyone will tell you a Thoroughbred, though a distant relative, is not an Arabian. This variation raises the question of relativity in conformation standards.
“All horses adapt to conditioning and occupation,” says Sue Stover, DVM, PhD, Dipl. ACVS, of the University of California, Davis. “I think we select for some of these traits, but whether that is a byproduct of conditioning or selection, I don’t know.”
In other words, while we might breed horses for specific types of muscling and conformation, we also enhance those traits through training and exercise.
In a 2010 study Brooks et al. examined the genetic relationship between skeletal traits such as bone length and thickness and discovered that these characteristics vary widely across the equine species, but they differ little within a breed. This might suggest that humans, over time, have selected for and, thus, carefully refined certain breeds’ conformation according to the animals’ intended use.
For instance, riders have long sought horses with traits such as a long neck for jumping. Several studies support this preference:
In a 2006 study in which they compared National Hunt (steeplechase) horses with horses that race on the flat, Weller et al. found significant differences in a number of traits, including various joint angles, wither height, and neck length. “National Hunt horses had the (larger) average values for all of these measurements compared to the flat horses,” they concluded.
Horses with longer backs are likely to perform better over jumps, Beeman says. “Stadium jumpers will be what we consider long in the back,” he says. “But if they’re too long or don’t have the right structure in the hind limbs, they won’t get lift.”
He also notes the value in a long neck: “A long neck, in my opinion, is a virtue in every horse that I deal with in today’s world. Yet, with every good thing comes some responsibility. Those long-necked horses are probably more prone to laryngeal hemiplegia (paralysis of one or both arytenoids—cartilages that form either side of the trachea entrance—resulting in respiratory noise also known as roaring). The left recurrent nerve has to travel long way in those horses.”
While, probably not surprisingly, limb conformation seems to have a greater impact on a horse’s risk of getting injured, researchers have identified at least one upper body trait that has a positive correlation to injury in racehorses. Anderson, McIlwraith, et al. found that the length of the bottom line (underside) of the neck impacted Thoroughbreds’ risk of having fetlock problems. “For every 10-cm increase in length of the bottom line of the neck, the odds of having effusion (excess fluid in the joint space) in the front fetlock increased by a factor of 5.1,” they said. The authors admitted, however, that they did not expect this correlation. “The effect of length of the bottom line of the neck on fetlock problems is interesting and could be related to increased weight.”
In the same study they noted, “Perhaps the most important findings from this study are the conformational variables that did not affect musculoskeletal disease, including wither and croup height; lengths of topline of neck, humerus (a bone in the horse’s forearm), radius (the upper foreleg bone ending at the knee), third metacarpus (cannon bone), femur (the long upper bone of the hind leg), tibia (the inner of the two bones that extends down from the stifle to the hock), third metatarsus (splint bone), and pastern; and angles of scapula (shoulder blade), scapulohumerus (connecting the humerus to the scapula), pastern, and hocks.”
Beeman believes that because horses bear most of their weight on the front limbs, any conformation trait that increases the stress, strain, and concussion on these limbs is likely to increase an animal’s lameness and injury risk. This might explain the association between neck bottom line length and fetlock swelling. If those horses have thicker necks than other horses with the same neck topline length, the additional mass could add to the load on the front end.
When we select horses for performance within a narrow range of conformational qualities, we might inadvertently limit their overall health and function. “The thing that I believe has kept the Quarter Horse, for instance, out of the quagmire of human interference,” says Beeman, “is all the athletic endeavors they have for those horses. Ranch horse competitions are more popular than halter these days; those horses have to work. That helps the Quarter Horse stay one of the leading breeds. Many owners don’t care how pretty the horse looks as long as they can do the job.”
Ultimately, though we breed the horse to suit the job, the job must suit the horse. By watching them closely we can determine their potential. “They’ll attempt to do the job they’re capable of,” Stover says. “That doesn’t mean conformation doesn’t play a role.”
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