CRUCIAL CONFORMATION, PART 2

THE SKELETON

When choosing or evaluating a horse, there are many factors to consider: breed, breed type (how the horse embodies the characteristics of his breed or type), pedigree, colour, temperament and personality. However, the most important element is the conformation, particularly if you want the horse to have an athletic career or breed. Choosing a horse based on an understanding of conformation makes it less likely that you will endure the disappointment or heartbreak of a career-ending injury or early loss of use due to arthritis or injury.

A horse with good conformation has no apparent faults that detract from his general appearance and function. Crucially, however, conformation is not just about looks but also about suitability for the job the horse will be asked to do. Some of the 'rules' of conformation are based on pure physics – structural strength, leverage forces and proper angles, for instance – and these help us understand why some horses stay sound, and others do not.

Of course, some horses with poor conformation go on to be winners, but these are truly the exception to the rule. Most of the best equine athletes possess certain qualities of good conformation that enable them to perform at a higher level. Generally, the horse with good conformation and proper body and leg angles experiences less wear and tear on joints and other structures. He is more apt to stay sound and perform well during a long life of athletic service than a horse with serious conformational flaws.

Bone structure

The horse's bone structure is determined principally by genetics but influenced to some extent by nutrition. Although improper nutrition when a horse is young and growing can damage an inherently well-conformed skeletal structure, adequate nutrition can't do much to improve an inherently poor structure.

Some leg deformities in foals can be helped with surgery or corrective trimming or hooves while the leg bones are still growing, but for the most part, a horse's basic structure is present at birth and cannot be changed. Likewise, no amount of muscle conditioning to try and improve a horse's appearance can change his basic conformation, although some faults can be somewhat disguised by good muscle development or fat covering. For these reasons, the skeletal structure must be carefully evaluated when selecting or judging a horse.

The significance of the spinal column

"If a breeder could breed the perfect spine, they could be certain of breeding the perfect horse." - Unknown

Ultimately, the conformation of any animal depends on the shape and characteristics of the spinal column. The horse's backbone ties the skeleton together, and all other structures attach to the spine, whether directly or indirectly.

Types of vertebrae

The vertebrae vary in shape according to their position within the vertebral column. There are seven cervical vertebrae, 18 thoracic vertebrae (the first nine of which comprise the withers), six lumbar vertebrae, five fused bones in the sacrum and 15-20 small tail bones.

The different sections of a horse's back can vary in length among individuals depending on the shape of these various types of vertebrae, and for this reason, horses may have short or long necks, and short or long backs.

The ribs attach to the thoracic vertebrae. The pelvic bones are connected to the spine between the lumbar vertebrae and the sacrum (at the lumbosacral joint), creating an attachment for the hindlegs. Muscular development of the shoulder, loins and hindquarters, therefore, depends a great deal on the conformation of the spine.

Shape of the vertebrae

Each vertebra in the spine has transverse processes (bony projections, like wings, that stick out to either side) and a dorsal spinous process (a bony projection that sticks out at the top). The dorsal spinous processes are short in the neck bones and along the back where the rider sits, but the 6-10 vertebrae that make up the withers have dorsal spinous processes that gradually increase to about 15cm in height and then diminish. This forms the characteristic curve to the wither and is where the muscles that hold the shoulder blade attach. The transverse (lateral) processes, or side wings, of the lumbar vertebrae, are wide to create an attachment for the large muscles of the back and quarters, which power the horse's actions as he jumps or moves at higher speeds.

Pelvis

The hindlegs attach to the spine through the pelvis, which is a bony girdle made up of several fused bones. Each side of the pelvis is a flat semicircle made up of the ilium, ischium and pubis, which are fused together to appear as one large bone. The hindlegs attach the pelvis at the hip joint. The pelvis also has several projections to which various large muscles attach, giving the hindquarters their shape. The positioning of the pelvis in the horse is slanted, not upright, and the angle of this 'slant' varies with the breed and the individual horse. The degree of angulation influences the shape of the rump and the general conformation of the hind leg.

Shoulder angle

The upper end of the scapula is attached to the backbone along the withers by muscles. The angle the shoulder blade forms with the backbone depends on the position and shape of the vertebrae. If the vertebral bodies are long (from front to back), this creates a long withers area, and the top of the shoulder blade will lie farther back than if the vertebral bodies are short. If the vertebral bodies are short, the top of the shoulder blade will lie closer to the base of the neck. The shoulder will thus be more upright, resulting in more concussion and jarring forces in the front legs.

Spinal flexion

In a horse, the range of movement in the neck is sizeable, but along the rest of the back, the range is very limited. In the thoracic region, there is very little movement at all, and in the lumbar region, there is some up-and-down and sideto-side movement. Ultimately, this is because the horse's spine is designed for rigidity and gives a stable point of reference and leverage for the powerful hindquarters to act through, allowing the force to be transmitted forwards with minimal energy loss.

The three main joints in the spine that allow extensive up-down movement are:

• The occiptoatlantal joint between the head and the neck.

• The cervicothoracic joint between the neck and the thoracic vertebrae.

• The lumbosacral joint joins the last lumbar vertebra to the sacrum.

The occipitoatlantal joint allows the horse to flex at the poll behind the ears to either poke his nose straight out or hold it close to his chest. The cervicothoracic joint enables the horse to lower or raise his head. The lumbosacral joint allows the horse's pelvis and hindquarters to rotate forwards so his hindlegs can reach further beneath his belly when he moves, giving him a longer stride. This junction is of enormous significance for the horse's athletic performance, allowing him to create a strong push when jumping and achieve higher levels of collection.

How the limbs attach to the backbone

The horse's skeleton exemplifies design perfection, embodying basic principles of leverage and physics. The shock-absorbing characteristics and muscular suspension of the front legs and shoulders are remarkably designed to reduce damage to these structures. The shoulders of the horse are not attached via bones to the spine; instead, the body is suspended between the shoulders and supported by muscle attachments that are ideal for minimizing concussive forces.

Conversely, the hindlegs are firmly and directly attached to the spine and pelvis, allowing the horse to have a perfect union of hindlegs and body for creating maximum power and forward propulsion without wasting energy. This means that the hindlegs must be properly constructed and aligned to absorb concussive forces. This requires appropriate angles in the hocks and stifles and a concave sole in the hindfoot that can flatten when the horse bears weight.

Take home message

From all of this, it is clear why the skeleton builds the foundation of conformation and also why some conformation issues cannot be compensated for. For these reasons, it is always a good idea to look at the skeleton, not just the musculature, when purchasing a horse for any discipline.