CRUCIAL CONFORMATION, PART 10: CHEST CONFORMATION
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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 exceptions 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.
In this issue, we start to look at chest conformation and how this impacts the athletic horse.
Chest conformation
The horse’s ribs form the outer surface of the chest and define the appearance of the horse’s midsection or barrel, the area between the front legs and hindquarters. They serve to protect the heart, lungs, arteries and windpipe.
The shape and curvature of the ribs ultimately determine whether a horse has a well-rounded, deep barrel with plenty of room for the heart and lung expansion or a narrow, flat-sided midsection. Ideally, the ribs should be curved and projected backwards rather than straight down. There should also be relatively large spacing between the ribs to allow for greater movement and lung expansion when the horse takes a breath.
The shape of the chest is, therefore, ultimately significant because it plays a major role in the horse’s level of stamina and endurance. A horse doing a lower level of work may not be hampered by chest conformation that limits lung capacity, but any horse that needs to perform work involving speed, power or endurance needs as much room as possible in his chest for maximum long expansion.
Anatomy
The thorax, or chest, is the front part of the barrel of the horse. The chest cavity is formed by the flexible, curved rib bones, which are attached to the backbone vertebrae at the top. The ribs in the front section of the chest are attached to the sternum, or breastbone, underneath the horse. The sternum lies between the forelegs and consists of six to eight bony segments connected to one another by cartilage to create the floor of the thoracic cavity. The width of the sternum, therefore, partially determines the width of the horse’s front end.
When viewed from the front, the chest, also called the breast, is defined as the area between the bottom end of the neck and the tops of the front legs.
An oval-shaped chest
The horse’s chest is long from backbone to breastbone and narrower from side to side, i.e. it forms an oval shape. The ribs are the skeletal support of the side of the chest. Just to the inside of the ribs are the scapular or shoulder blades. These attach to the humerus, the uppermost bone in the front leg, between the shoulder joint and elbow joint. [end box]
Ribs
Most horses have 18 pairs of ribs, though some have 19, and a few only have 17. The number of ribs depends on the number of thoracic vertebrae because the ribs are attached to these vertebrae. Some Arabians and Thoroughbreds have 19 pairs of ribs but compensate by having five lumbar vertebrae instead of six. This conformation creates a shorter, stronger loin area or coupling. The extra rib gives a well-ribbed-up appearance and depth of flank. The underline of the horse should rise gradually toward the hindquarters, not up sharply towards the flank.
Rib attachments
- The first rib is the shortest and angles slightly forward from its vertebrae.
- The second rib is vertical.
- The remainder of the ribs (after the second)should slope backwards rather than straight down.
- The first six or seven ribs are found behind the scapula.
- The first ten thoracic vertebrae have the tallest dorsal spinous processes, which create the withers.
- The first nine rib pairs provide attachment sites for muscles that activate the shoulders.
- The first eight pairs of ribs, the sternal ribs, are attached at their bottom end to the sternum with cartilage.
- The last ten or eleven pairs are attached only to the backbone and not to the sternum.
- The last eleven pairs of ribs (or ten or nine, depending on the horse and his total number of ribs) are linked together at the bottom by only a band of cartilage and thus have greater mobility. Those last ribs allow for maximum chest expansion when the horse breathes, rotating into their widest position.
- The last one or two pairs are often termed floating ribs because the bottom end may not be attached to the adjacent ribs.
Well-ribbed up
It is important that the ribs extend back along the abdomen to allow for maximum chest expansion. Arabians and horses with Arabian blood, like Thoroughbreds, which may have the extra pair of ribs, often have great lung room and exceptional endurance due in part to the extra ribs.
For a horse to be well-ribbed up, the thoracic vertebrae that carry the ribs should extend back toward the pelvis, leaving no slackness between the last rib and the hip and very little space between the rib and the angle of the hindquarter. The horse with well-sprung ribs that curve out and project backwards has a round barrel and a short loin (short back).
Muscles of the chest
The chest is not rigidly attached to the front legs but is suspended between them, supported between the shoulder blades by muscles. The primary muscle attachments are at the bottom of the rib cage and suspend the chest from the sides of the forelegs. This is an ideal arrangement for minimizing concussion forces for the body, as muscular attachments have more elasticity than bony attachments and can absorb much of the shock that would otherwise be transmitted directly to the body through the feet and the legs. This suspension arrangement also minimizes jarring of the heart and lungs, the principal organs within the chest cavity.
In addition, many of the muscles associated with the neck and front legs are attached to the ribs. When viewed from the front, the chest should be well-defined rather than blending into the neck. Even if the horse has thick muscling, the actual width of the chest is defined by the bone structure. The breast should be wide, with a relatively wide gap between the front legs, but not too wide, or the horse will have less agility and speed.
Next time
In our next edition, we will continue to examine the conformation of the chest, particularly in terms of its shape. The shape of a horse’s chest plays a significant role in his performance ability, so stay tuned for our next edition.