Equine conformation evaluates a horse's bone structure, musculature, and its body proportions in relation to each other. Undesirable conformation can limit the ability to perform a specific task. Although there are several faults with universal disadvantages, a horse's conformation is usually judged according to its intended use. Thus "form to function" is one of the first set of traits considered in judging conformation. A horse with poor form for a show jumper could have excellent conformation for a cutting horse or draft horse. Every horse has good and bad points of conformation and many horses excel even with conformation faults.
The following is a list of desirable or faulty characteristics of the 'points' of a horse, or its anatomical parts, concentrating especially on North American breeds.
Head and neck The standard of the ideal head varies dramatically from breed to breed based on a mixture of the role the horse is bred for and what breeders, owners and enthusiasts find appealing. Breed standards frequently cite large eyes, a broad forehead and a dry head-to-neck connection as important to correctness about the head. Traditionally, the length of head as measured from poll to upper lip should be two-thirds the length of the neck topline (measured from poll to withers). Presumably, the construction of the horse's head influences its breathing, though there are few studies to support this. Historically, a width of 4 fingers or 7.2 cm was associated with an unrestricted airflow and greater endurance. However, a study in 2000 which compared the intermandibular width-to-size ratio of Thoroughbreds with their racing success showed this to be untrue. The relationship between head conformation and performance are not well understood, and an appealing head may be more a matter of marketability than performance. Among mammals, morphology of the head often plays a role in temperature regulation. Many ungulates have a specialized network of blood vessels called the carotid rete, which keeps the brain cool while the body temperature rises during exercise. Horses lack a carotid rete and instead use their sinuses to cool blood around the brain. These factors suggest that the conformation of a horse's head influences its ability to regulate temperature.
Face The front of a horse's face when viewed from the side will usually be straight from the forehead to the nostrils. A Roman nose is a facial profile that is convex, and is often associated with draft horses. A dished face is a concave profile with a dip in the face between the eyes and nostrils, usually associated with Arabians. The muzzle is the lower end of the head, and includes the nostrils, upper and lower lips, and the front teeth.
Eyes
A horse with pig eye has unusually small eyes. This is primarily an aesthetic issue, but claimed by some to be linked to stubbornness or nervousness, and thought to decrease the horse's visual field.
Jaw size The lower jaw should be clearly defined. The space between the two sides of the jawbone should be wide, with room for the larynx and muscle attachments. The width should be 7.2 cm, about the width of a fist. The jaw is called narrow if the width is less than 7.2 cm. The jaw is called large if it is greater than 7.2 cm. A large jaw gives head a false appearance of being short and adds weight to the head. Too large a jaw can cause a reduction to the horse's ability to flex at the poll to bring his head and neck into proper position for collection and to help balance.
Jaw position
A parrot mouth is an overbite, where the upper jaw extends further out than the lower jaw. This can affect the horse's ability to graze. Parrot mouth is common and can be managed with regular teeth floating by a veterinarian. A monkey mouth, sow mouth, or bulldog mouth is an underbite, where the lower jaw extends further out than the upper jaw. This is less common than parrot mouth. This can affect the horse's ability to graze. Monkey mouth is common and can be managed with regular teeth floating by a veterinarian.
Ears Ears should be proportional to the head. They should be set just below the level of the poll at the top of the head. Ears should be a position where they can be rotated forward and backward. Ears that are too large or too small may make the head seem too small or large in proportion with the body.
Neck length and position A neck of ideal length is about one third of the horse's length, measured from poll to withers, with a length comparable to the length of the legs. An ideally placed neck is called a horizontal neck. It is set on the chest neither too high nor too low, with its weight and balance aligned with the forward movement of the body. The horse is easy to supple, develop strength, and to control with hand and legs aids. Although relatively uncommon, it is usually seen in Thoroughbreds, American Quarter Horses, and some Warmbloods. Horizontal neck is advantageous to every sport, as the neck is flexible and works well for balancing. A short neck is one that is less than one third the length of the horse. Short necks are common, and found in any breed. A short neck hinders the balancing ability of the horse, making it more prone to stumbling and clumsiness. A short neck also adds more weight on the forehand, reducing agility.
A short, thick, and beefy neck with short upper curve is called a bull neck. The attachment to its body is beneath the half-way point down the length of shoulder. Bull neck is fairly common, especially in draft breeds, Quarter Horses, and Morgans. Bull neck makes it more difficult to maintain balance if the rider is large and heavy or out of balance, which causes the horse to fall onto its forehand. Without a rider, the horse usually balances well. A bull neck is desirable for draft or carriage horses, so as to provide comfort for the neck collar. The muscles of the neck also generate pulling power. A horse with bull neck is best for non-speed sports. Bull neck is not considered a deformity. A long neck is one that is more than one third the length of the horse. Long necks are common, especially in Thoroughbreds, Saddlebreds, and Gaited Horses. A long neck may hinder the balancing ability of the horse, and the horse may fatigue more quickly as a result of the greater weight on its front end. The muscles of a long neck are more difficult to develop in size and strength. A long neck needs broad withers to support its weight. It is easier for a long necked horse to fall into the bend of an S-curve than to come through the bridle, which causes the horse to fall onto its inside shoulder. This makes it difficult for the rider to straighten. A horse with this trait is best used for jumping, speed sports without quick changes of direction, or for straight line riding such as trail riding.
Neck arch and musculature
A neck with an ideal arch is called an arched neck or turned-over neck. The crest is convex or arched with proportional development of all muscles. The line of the neck flows into that of the back, making for a good appearance and an efficient lever for maneuvering. The strength of the neck with proportional development of all muscles improves the swing of shoulder, elevates the shoulder and body, and aids the horse in engaging its hindquarters through activation of the back. An arched neck is desirable in a horse for any sport.
A ewe neck or upside-down neck bends upward instead of down in the normal arch. This fault is common and seen in any breed, especially in long-necked horses but mainly in the Arabian Horse and Thoroughbred. The fault may be caused by a horse who holds his neck high (stargazing). Stargazing makes it difficult for a rider to control the horse, who then braces on the bit and is hard-mouthed. A ewe neck is counter-productive to collection and proper transitions, as the horse only elevates its head and does not engage its hind end. The horse's loins and back may become sore. The sunken crest often fills if the horse is ridden correctly into its bridle. However, the horse's performance will be limited until proper muscling is developed. A swan neck is set at a high upward angle, with the upper curve arched, yet a dip remains in front of the withers and the muscles bulge on the underside. This is common, especially in Saddlebreds, Gaited horses, and Thoroughbreds. A swan neck makes it easy for a horse to lean on the bit and curl behind without lifting its back. It is often caused by incorrect work or false collection. A knife neck is a long, skinny neck with poor muscular development on both the top and bottom. It has the appearance of a straight crest without much substance below. A knife neck is relatively common in older horses of any breed. It is sometimes seen in young, green horses. It is usually associated with poor development of back, neck, abdominal and haunch muscles, allowing a horse to go in a strung-out frame with no collection and on its forehand. It is often rider-induced, and usually indicates lack of athletic ability. Knife neck can be improved through skillful riding and the careful use of side reins to develop more muscle and stability. A knife necked horse is best used for light pleasure riding until its strength is developed.
Crest
A large crest can be found in any breed. It is most often seen in stallions, ponies, Iberian breeds and draft breeds. There is often a link to the animal being an easy keeper. An excessively large crest puts more weight on the forehand, and is associated with insulin resistance. Crest enlargement is caused by fat deposits above the nuchal ligament. In most horses, the crest can be reduced with a controlled diet.
Shoulder, forearm, and chest
The horse's shoulder includes the shoulder blade and the upper arm. Its angle and length influence stride length, smoothness of movement, and the ability to absorb concussion. A shoulder may be described as upright or sloping. A sloping shoulder allows for a longer, smoother stride and better shock absorption, where horses may move with more reach and may be more comfortable to ride. An upright shoulder tends to shorten the stride and increase concussion on the front legs. Horses with upright shoulders may have higher knee action and a less elastic gait.
The upper arm (humerus) connects the point of shoulder to the elbow. Its length and angle affect how freely the horse can move the foreleg. An upper arm that is somewhat shorter than the shoulder blade, and forms an open angle with it, allows good reach and freedom of movement. A short upper arm can restrict the stride and make the horse appear to move with a shorter, choppier action. A very long upper arm may place the forelegs farther under the body, which can limit the forward swing of the leg.
The elbow is the joint at the back of the upper arm. The elbow should point straight back and sit close to the body without being tight against it, allowing the foreleg to move straight and freely. Turned‑in elbows may cause the toes to turn out, and turned‑out elbows may cause the toes to turn in and can produce paddling or winging.
The forearm runs from the elbow to the knee and contains the major muscles that extend and flex the foreleg. An ideal forearm is long, well‑muscled, and aligned straight with the knee and cannon bone. A long forearm is often associated with a longer stride and more efficient movement. A short forearm can shorten the stride and increase knee action.
The chest (usually viewed from the front) is formed by the ribs, breastbone, and shoulder region. Its width and shape influence lung capacity, stamina, and the placement of the forelegs. The chest should be well defined, with enough width between the shoulders to allow lung expansion and straight movement of the forelegs. A narrow chest may place the forelegs too close together, increasing the chance of one leg interfering with the other. A wide chest may set the forelegs farther apart, which can reduce agility.