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The enigma of conformation

This article has appeared previously with Equestrian Life. To see what's in the current issue, please click here.

Galloping horse in paddock - Labelled for reuse

 

By Dr Maxine Brain

Conformation of the horse is a very important aspect to evaluate when looking for both lameness and for pre-purchase assessment.

Whilst most horse owners can identify a very poorly conformed animal, there are many subtler conformation problems that are overlooked until the undesirable trait is pointed out by a more experienced horse person. Why is conformation such an important issue? Poor conformation will increase the risk of a horse becoming lame as a result of poor weight distribution, or increase stresses on one part of the body or limb. This does not mean that every poorly conformed horse will break down or that every well-conformed horse will stand up to the rigors of training.  It simply means the odds are greater a problem will occur.

An ideal conformation is desirable as it means that the pressures on the bones and the strains on the soft tissue structures are equally divided both between legs and within legs. Thus the forces created when moving and landing on a limb are dispersed equally.
 
Although many people think good conformation is about having straight legs, there is a lot more to assessing good conformation than just the legs. In assessing conformation, the overall balance of the horse should be evaluated, as should the length of the neck and back, the chest size as well as other attributes such as shoulder and rump angles. It is important to note that different breeds will have different desirable conformation traits, which relate to the work they are required to perform. Therefore, it is difficult to make sweeping claims about the ideal conformation of a horse.

 



To assess a horse’s conformation, the horse should be evaluated both standing and walking on a firm flat surface. Not all conformation defects are visible in the standing horse, hence the benefit in watching a horse walk. When viewed from the side the horse’s body can be roughly divided into the forehand, the mid-body and the hindquarter. Each of these sections should be about equal in their proportion to the other two sections. If mentally a circle is used to encapsulate each of these areas, then they should overlap each other by roughly a third to be balanced. If they overlap too much then usually the horse will appear short in the back. If they don’t overlap or minimally overlap, the horse is usually too long in the back. The horse’s neck length should also be proportional to the body.

The height of the withers should be the same height as the height of the rump. This will not be the case in some growing horses as the rump is often higher during growth spurts, resulting in the expression of horses having to “catch up in the wither”.  The height to the wither should also be similar to the length of the body of the horse.

To assess leg conformation, the legs should be assessed from the front, back and side view.  Ideally with the front limbs, a line dropped from the point of the shoulder should divide the leg straight down the centre of the cannon, pastern and hoof wall. The back legs, when viewed from behind, should be equally divided by a line dropped from the point of the buttocks, down over the point of the hock, straight down the cannon bone to between the outside and inside heel.

When looking from the side, a line dropped from the centre of the elbow joint, should go down through the middle of the carpus (knee) and fetlock to end approximately 5cm behind the sole of the heel. A line from the point of the buttocks behind should drop straight, touching the point of the hock and running down the back of the hind cannon, ending approximately 7.5-10cm behind the hind foot.

Other factors to consider when assessing conformation are the shoulder and the rump. The shoulder should have a nice angle on it (which has been said to be around 45-50 degrees) and the shoulder angle and the angle of the pastern axis should be the same.

These angles are measured relative to the ground surface. The rump should be relatively flat and a have a low rump angle. This angle is measured by a line from the point of the buttocks behind up to the highest point on the lower back (vicinity of the tuber sacrale) relative to a line drawn from the point of the buttocks to the stifle joint.

Once the ideal conformation of a horse is known, it is easier to identify anatomical defects that are less desirable. Not all conformational defects are equally detrimental to the horse: the effect they have on the horse will be influenced by the type of work it is expected to perform and the age at which it is asked to perform.

 



The list of conformation defects is enormous and could fill a book. A few of the more common ones are:

1.    BASE-WIDE: The hooves are positioned wider apart than what they would be if ideally positioned, i.e. to the outside of an invisible line drawn from the point of the shoulder down. Horses with small, narrow chests are more likely to display this conformation. As the horse walks, this conformation results in the horse landing on the inside of the foot first, meaning it bears more weight on the inside of the leg. This constant disparity in weight distribution, and forces applied to the inside aspect of the limb, mean that damage is far more common to the inside structures of the leg. Examples of common ailments with this conformation include medial (inside) heel bruising, ringbone and side bone.

2.    BASE-NARROW: The hooves are positioned closer together than ideal. Often these horses have a wide chest. The horse when walking will land on the outside aspect of the limb, resulting in the outside of the leg bearing the most weight and consequently the most damage is seen here. They are more likely to have lateral (outside) heel bruising, ringbone and sidebone.

3.    TOED-IN: The hooves when viewed from the front should face forward. Toed-in horses, as the name suggests, will have toes facing inward towards each other. This can often accompany other conformation defects further up the limb such as base-narrow conformation, offset knees or varus of the knees or fetlocks. Horses with this conformation tend to paddle when they walk, meaning they often swing the leg outwards as they bring the limb forward.

4.    TOED-OUT: The hooves when viewed from the front typically face outwards. Toed-out horses usually are either base-narrow or base-wide, with the former being the more common combination. When associated with a base-narrow conformation, the horse will often swing its leg inwardly as it walks (winging) resulting in knocking the other limb.  There is a tendency for the horse to land on the outside aspect of the hoof. If associated with a base-wide conformation, then the horse will still swing its leg inwardly as it walks but lands on the inside of the foot. Toed-in horses can damage their inside splint bones and inside sesamoid bones from physically hitting them when swinging the leg inwardly when moving.

5.    OFFSET KNEES: The cannon bone should be central to the carpus or knee. With offset knees, the cannon bone usually sits more under the outside aspect of the knee so that the imaginary line dropped from the shoulder runs down the inside of the cannon bone. This means that the weight is concentrated more on the inside of the cannon, and also on the inside splint bone. Often these horses will develop splints on the inside of the leg, particularly up higher on the cannon and under the knee.

6.    BACK AT THE KNEES: The knee if viewed from the side sits back from an invisible line dropped from the centre of the elbow joint. This conformation can often lead to lameness issues as it increases pressure on the front aspects of the small knee bones - making the knees very prone to chip fractures. The soft-tissue structures, in particular the ligaments at the back of the leg, are also subject to increased straining because of this conformation.

7.    OVER AT THE KNEES: The knee if viewed from the side is usually forward of the line from the centre of the elbow. This does not place the same amount of strain on the knee cones or ligaments of the knee as being back at the knees does. It can be seen commonly in newborn and young foals as a result of contracture of the flexor ligaments behind the knee, and many of these will resolve as the foal ages. In cases of severe contracture of the flexor ligaments, surgery may be required; but this is not really what I would consider a conformation issue but a congenital abnormality, so shall not be discussed any further in this article.

8.    OUT AT THE KNEES: This can also be known as “bow legged” and refers to the legs of horses where the knees are out wider than a line dropped from the shoulder when viewed from the front. Vets will often call this a “varus” of the knees. This conformation places a lot of pressure on the inside of the knee joints as well as extra strain on the outside ligaments of the knee.

9.    IN AT THE KNEES: The opposite to out at the knees, the knees are inward of a line dropped from the point of the shoulder when viewed from the front. They appear to be “knock-kneed’ and may be referred to by the vet as having a “valgus” deviation of the knees. This is commonly seen in young foals and can improve as the foal grows and develops in the chest muscles. It places increased pressure on the outside bones and joints of the limb and increased strain on the ligaments on the inside of the leg.

10.    SICKLE HOCKED: This conformation defect is seen when looking at the hindlegs from the side. A well-conformed horse should stand with his cannon bones straight, not on a sloping plain to the ground causing a more angled appearance to the hock relative to the cannon bone. There places more pressure on the front of the hock bones and increased strains on the ligaments at the back of the hock (curbed hocks being one of the more well-recognised results of this conformation).

11.    STRAIGHT BEHIND: The angle of the stifle and the hock are quite big resulting in the tibia (the bone between the hock and stifle) appearing to be closer to straight up and down than a nice angle. These horses are very prone to locking their stifles, more appropriately called “upward fixation of the patella”.  Horses also tend to place more pressure on the soft-tissue structures of the hock and suffer with increased fluid in their upper hock joints (bog spavin).

12.    UPRIGHT PASTERNS: The pastern angle should ideally mirror the angle of the shoulder and should be in the range of 47-55 degrees (there is not uniform agreement on this angle). When the pastern angle is larger than this the horse is said to have upright pasterns. This type of conformation tends to put more forces through the bone and less on the soft-tissue structures, resulting in degenerative problems of the joints such as arthritis and ringbone.

13.    LONG, SLOPING PASTERNS: The pastern angle is less than the shoulder angle and is typically seen in horses with long toes and low heels. This type of conformation places increased strains on the soft-tissue structures at the back of the limb, in particular the flexor tendons and the suspensory apparatus. 

14.    BROKEN BACK PASTERN AXIS: Ideally when viewed from the side, an imaginary line drawn down the front of the hoof wall should be parallel to an imaginary line drawn down the front of the pastern. When the pastern is broken back, the angle of the hoof is less than the angle of the pastern. This is also seen when the toes are allowed to grow too long and the heels become underrun. This puts strain and pressure on many structures associated with the foot, causing ongoing or chronic lameness issues such as deep digital flexor strain, heel bruising, quarter cracks and coffin joint pain.

15.    BROKEN FORWARD PASTERN AXIS: The angle of the hoof is larger than the angle of the pastern, giving the broken forward appearance. Similarly, this conformation also causes some chronic injury worries because of the uneven loading of the foot, including coffin joint pain, inflammation of the pedal bone (coffin bone) and suspensory ligament injuries.

16.    CLUB FOOT: This condition can be seen both as a congenital issue (something the horse is born with) or it can be acquired as a result of an injury or nutritional imbalance. The angle of the hoof wall is much greater than with a “normal” foot and typically has an angle around 60 degrees or more. These horses are prone to getting bruised toes because they tend to land toe first.

17.    SHORT IN THE BACK: As the name suggests, these horses appear short in the back. When viewed from the side, the back should be about a third of the body length, equal in proportion to the forequarter and hindquarter. Horses that are short in the back tend to be less flexible in their backs and are prone to develop injuries of the vertebrae.

18.    LONG IN THE BACK: When viewed from the side these horses appear longer in the back than either the fore or hindquarter. The back has more flexibility, but as a consequence is more prone to soft-tissue injuries of the back.

19.    ROACH BACK: This can be a conformation fault or it can develop as a result of an injury. If viewed from the side the back has a convex appearance (curves upward) in the lower back region, forward of the sacroiliac area. The vertebrae will often not move well and this will affect the movement of the horse behind.

20.    SWAYBACK: When viewed from the side, the horse’s spine appears to be concaved (curves downward) from the withers back to the pelvis. This can be quite a marked concavity and is more likely to be associated with long-backed horses. Horses are prone to sore muscles and ligament damage along the back.

 

 

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