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Leg Conformation

Good leg conformation in a horse is a must if that animal is to remain serviceably sound for a lifetime of work and performance.

Photo: Thinkstock

Good leg conformation in a horse is a must if that animal is to remain serviceably sound for a lifetime of work and performance. No matter how beautiful or well-pedigreed a horse, it will matter little if the animal suffers from chronic lameness. No legs, no horse.

Often when discussing good leg conformation, we use the term "straight legs." If that term is taken at face value for all parts of the leg, it is totally inappropriate. For certain parts of the leg, we should, instead, be discussing correct angle.

Oldtimers loved to use the term "flat bone" when talking about good leg conformation. Technically, there is no such thing as a "flat" bone in a horse’s leg. The bones are round, or oval-shaped. What these horsemen are referring to is a lower leg with solid, round bones backed by appropriately sized tendons and ligaments. When viewed from the side, such a healthy leg will give the appearance of being flat.

Proper leg conformation for the equine is highly important in all of its endeavors. This is especially true of horses in the wild, where nature is a ruthless culling agent. The wild horse whose legs give out because of poor conformation might wind up being an evening meal for a predator. While wild horses in general might not look like show ring models, it is seldom that one will find wild horses with serious leg conformation problems. Most wild horses with poor leg conformation don’t make it to adulthood.

The domestic horse doesn’t face that type of brutal culling. Expensive therapeutic shoes and procedures might be involved in straightening out a foal’s crooked legs. In a friendly environment, helped by modern science, it has a much better chance of growing up and becoming a useful horse than would its wild counterpart with the same problem.

This is always a good news/bad news scenario. The good news is that the horse can be turned into a serviceable animal which will survive its malady and provide its owner with many enjoyable outings. The bad news is that if this horse becomes part of a breeding program, the problem, if heritable, could be passed on to another generation, sometimes without the knowledge of the people breeding to the horse.

Even when we breed a horse with good leg conformation to another which has good legs, we are not guaranteed that the foal will have proper conformation. However, the odds are much more on our side than they are when one of the parents has poorly conformed legs.

Horses must be able to move forward if they are to be useful to man. For some trail horses, all that might be asked is to move forward at a walk over gentle terrain. Others, however, might be asked to move forward while climbing a rocky trail that leads to the top of a mountain. For still others, moving forward means cantering across an arena and sailing over obstacles on a jumping course. There are those which are asked to run at speed around an oval track with money, honor, and glory awaiting the winner. Still others will race in a cloverleaf pattern around barrels, putting tremendous torque on bones, tendons, and muscles as they scramble through the tightest of turns.

Whatever the use to which it is put, it's unlikely that a horse will remain sound and serviceable for performance after performance or ride after ride if it doesn’t have properly conformed legs. Even horses which have properly conformed legs often can wind up being lame as the result of over-exertion or injury. When the leg is poorly conformed, the problems are compounded.

We should always bear in mind that there are many things about a horse we can change, but some things we cannot. If a horse is thin, we can provide extra nourishment so that it gains weight. If it is out of shape, we can launch an exercise program for it that will strengthen muscles and tendons. If it has bad teeth, we can help correct the problem by calling in a dental specialist.

If, however, the horse was born with improper leg conformation, there really is nothing we can do about it by the time the horse is an adult. Corrective shoeing might help somewhat, and corrective devices can be effective in straightening crooked legs in a foal, but that is about it. Despite taking these steps, nothing will have changed the fact that the horse was born with improper leg conformation and continued soundness is at risk.

There are, of course, exceptions to every rule. Some horses perform well with conformation faults. I remember a three-gaited National Show Horse which won national championships even though he had a serious conformational fault in one leg. I have mentioned in the past that one of my very best trail horses traveled up and down mountains for years and never took a lame step, even though one of his front legs was cocked at an angle. There also have been racehorses which have beaten the odds and won stakes money despite being born with poor leg conformation.

However, for every exception to the rule there will be a thousand others with similar problems which are unable to perform. If one is in the market for a horse, it is far better to start with good leg conformation rather than hope you might have bought an exception.

Front End Conformation

When talking leg conformation, the discussion normally starts with the front end. There is a valid reason for that. The front limbs support as much as 65% of the horse’s weight when at rest. That’s just when the horse is standing still. When it is running at speed or jumping, strong concussive forces are added to the weight bearing. At one point in every stride when a horse is galloping, all of the weight comes to bear on the leading foreleg. Near the end of a race, when fatigue is becoming a factor, the poorly conformed foreleg is in jeopardy every stride.

We are indebted to Professor Byron Good for the phrase "form to function" when discussing proper conformation. Good was not saying that every horse should be constructed alike. Far from it. The best "form to function"is vastly different if you are looking for a racehorse which can run a mile as compared to a cutting horse which only makes short spurts, sliding stops, and quick turn-arounds in a relatively small pen. The legs of the cutting horse will typically be shorter and stouter than its counterpart which is asked to run a mile or more at speed.

Thus, there should be differences in leg types for horses which are used for various events. But no matter what the use, correct leg conformation remains the same, whether we are discussing a 17-hand, long-legged racehorse or a 15-hand stout, short-legged cutting horse.

When we take a look at the horse’s front legs to determine whether they have good conformation, we will use the aforementioned terms "straight" and "angle." When looking at the horse’s front legs from a head-on position, we want to see a straight leg. When viewing it from the side, we want to see proper angle at certain points, such as the fetlock.

If all of the bones, tendons, and ligaments, as we view the horse from the side existed in a perfectly straight line from bottom to top, the horse’s leg would be unable to serve its function of shock absorber. The perfectly straight leg would send direct concussion from ground level up and into the horse’s body without impediment during each step.

When foot, fetlock, and shoulder are properly angled, however, much of the concussion is dissipated along the way.

Before we get any further into the discussion on proper angle, let’s take a look at the rest of the bone structure from shoulder to foot. The horse’s shoulder bone or scapula is a broad bone that connects to the next bone in line—the humerus. The humerus angles down and rearward and joins the radius or forearm at the elbow. The radius, in turn, extends downward to the knee or carpus. Connecting to the bottom part of the carpus is the metacarpus or cannon bone, which runs down and into the pastern. The long pastern bone is known as the first phalanx or P1. It fits into the second phalanx or P2, also known as the short pastern bone. The second phalanx fits into the third phalanx or P3, more commonly known as the coffin bone.

Just behind the cannon bone, where it joins the long pastern bone, are the sesamoid bones, which serve as pulleys for the superficial and deep flexor tendons. Another bone of the foot that is heavily involved with the suspensory ligaments is the distal sesamoid bone, located at the junction of the short pastern bone and the coffin bone. Its common name is the navicular bone.

There are two other bones in each of the front legs. They are located on either side of the cannon bone and are known as the splint bones. They support the bones of the knee and help to dissipate energy transmitted to the metacarpal region. The general belief is that they are evolutionary remnants from the prehistoric three-toed horse. Although they serve little practical purpose today, they can, nevertheless, be involved in lameness problems.

Let's start with the side view of the front leg, seeking to establish just what are appropriate angles.

Angles

A horse with good conformation will have a front shoulder that is laid back or angled at an appropriate degree. Just exactly what the degree is will vary from horse to horse. Having the proper angle is key to the horse’s stride. If the shoulder is steep and straight, the horse’s stride will be short and choppy, which translates into discomfort for the rider. The horse’s front feet will hit the ground more often over a given distance, with the concussion from each stride traveling all the way up the leg and into the body.

When looking at the horse from the side, check the angle formed by the ground under the hoof and the slope of the pastern. As is the case with the shoulder, this angle will vary from horse to horse.

Often a horse will have about the same degree of angle to its pastern as it does in its shoulder. Many old timers used to claim that horses with the best conformation had front pasterns at a 45-degree angle to the ground. That theory is no longer considered valid. There is no universal degree for all horses. Today, 45 degrees would be considered the minimum acceptable angle in front for most horses.

One thing is a must if a horse is to have properly conformed front legs—the slope of the pastern must be identical to the slope of the foot. If identical, there will be a precise and smooth insertion of the long pastern bone into the short pastern bone and of the short pastern bone into the coffin bone. If these bones do not mesh correctly, strain is placed on tendons and ligaments and lameness often results.

So what should we be seeing when viewing a properly conformed leg from the side? When a horse is viewed in profile, one with good conformation will appear to have a straight, vertical alignment from the middle of its forearm all the way to the ground just behind its heel. The angles should be at the shoulder and pastern. The rest of the leg should be straight.

Now let’s step in front of the horse. Here, again, we can use the term "straight leg." When looking at the horse from the front, superimpose a mental vertical line. It should travel in a straight path from the point of the shoulder, through the middle of the forearm and down the cannon bone, pastern, and foot. No angles there. Just a straight line. Any deviations are aspects of poor leg conformation.

We also want to see the same distance between the forearms at the chest as between the two feet on the ground. If the distance is narrower at the feet, the horse is said to be base-narrow. If the reverse is true, the horse is said to be base-wide.

One of the most serious front leg conformational defects is called toeing out. When looking at the horse with our straight vertical line imposed, we will observe that the toes are turned outward and the line, instead of traversing the center of the foot, will be to the inside. A horse with this fault is gong to put extra stress on the inside of its knee with every stride. There is another problem when dealing with this fault. As the horse travels, particularly at the trot, it will wing in. This poses a constant danger to the horse of striking the sesamoids, the splint bones, or the coronet band of its opposite foreleg.

The reverse problem occurs in a horse which toes in or is pigeon-toed. In that case, our line will be to the outside of the foot, rather than straight down the middle. Such a horse will have a tendency to wing out or paddle when it moves, but at least it generally isn’t in danger of striking itself.

A fault that is in the same category for severity as the toed out horse is one that has bench (or offset) knees. This means that the forearm and cannon bone do not line up. Instead, the forearm will enter the knee on the inside or medial aspect while the cannon bone will exit more on the outside or lateral aspect of the knee (or vice versa). Such a horse is likely to develop knee trouble when asked to perform in a stressful discipline. Another is back-at-the-knee. When viewed from the side, the knee takes on a dished appearance. When placed under stress, especially if the tendons and ligaments are fatigued such as at the end of a race, the knee will overextend backward and can cause permanent injury.

The knee is something of a precarious structure at best and needs all the help it can get to avoid injury. When looking at an illustration or model of the knee bones, I always am reminded of children’s building blocks that are balanced in rows, one on top of the other. With that illustration in mind, it might become easier to understand why deviations from normal conformation, such as bench knees, can create serious soundness problems. Unless one bone blends smoothly into another at the joints, the effects of weight and concussion are not properly handled.

The key to checking front leg conformation is to observe the horse in motion as well as at rest. Corrective shoeing or trimming might diminish the appearance of some conformational defects, but man-made solutions to poor conformation cannot change the bone structure that caused the problem in the first place. The problem horse whose hooves have been modified to cover up a toeing-in or toeing-out problem might look straight and correct when standing, but the problem will often surface at the trot, sometimes in dramatic fashion.

Hind Limbs

We started with the front because that is where the most weight is borne. However, proper rear leg conformation is as important as proper front limb conformation if a horse is to remain sound. A horse which is unable to propel itself forward at the pace desired because of poorly constructed rear legs will not be suitable for riding or driving.

As with the front legs, good rear limb conformation is a must, no matter what the discipline. Trail horses traveling across mountainous terrain need strong, durable rear legs that can propel them up steep slopes and slow the rate of descent when coming back down. Jumpers need strong, sound rear legs to launch their bodies into the air. A cutting horse or reining horse has continuous need of strong, rear limbs for power, turning, and stopping. The same is true of upper level dressage horses. The list goes on.

As we did with the front legs, we will take a look at all of the bones involved in a horse’s rear limbs. We start at the spine where the ilium, the largest of three bones in the pelvis, connects with the spinal column. The angular shape of a the horse’s pelvis determines whether it has a flat croup or a sloped croup.

The ilium angles down and back to blend into the femur or thigh bone. The femur angles slightly forward to the stifle. Beginning at the stifle is the tibia, which continues down to the hock. From the hock to the pastern is the metatarsus or rear cannon bone, which flows downward into the long pastern bone, short pastern bone, and coffin bone.

Two areas at risk of lameness in the rear legs are the hocks and the stifles. The stifle is the joint at which the femur ends and the tibia begins. Relating it to human anatomy, the stifle serves the same function as a human’s knee.

The hocks play a key role because tendons pass over them to transmit energy from the muscles to provide propulsion. Unless the hock is properly conformed, each step produces undue stress.

How do we determine if a horse has good rear limb conformation? We’ll start by stepping directly behind the horse (at a safe distence, of course) for an assessment. First of all, we want to see the same distance between the hocks as we see between the feet on the ground. When observing from behind, the horse’s rear legs should be straight. If a vertical line were drawn on a photo taken from behind, the line would go as straight as a plumb line from the center of the buttocks downward through the center of the entire rear leg, including pastern and foot.

Now, let’s step to the side and take a look. When you look at the rear legs from this view, keep the term angulation in mind. The angle of the stifle and the hock should not be too straight or too angular, but should present a well-balanced picture with muscles running smoothly down the leg to the hock.

Using an imaginary plumb line again, we should be able to start it at the rear of the buttocks and drop a straight line downward to the hock and then along the cannon bone until it reaches the ground three to four inches behind the heel.

Any deviations indicate poor rear leg conformation that can range from one of the worst, being wide at the hocks, to one not quite so severe, being too narrow or cow-hocked.

Take-Home Message

So, go out and take a good look at your horse from the front and the side. Learn what is normal for him, and discuss his conformation with your veterinarian and farrier to learn what you should expect from him based on the sport or discipline in which you participate.

Good leg conformation is no guarantee that a horse will never take a lame step, but the chances are much more in our favor than they are with the horse that has poor limb conformation.

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 www.exclusivelyequine.com or by calling 800/582-5604.

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