Equine conformation

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 by what its intended use may be. Thus "form to function" is one of the first set of traits considered in judging conformation. A horse with poor form for a Grand Prix show jumper could have excellent conformation for a World Champion cutting horse, or to be a champion draft horse. Every horse has good and bad points of its conformation and many horses (including Olympic caliber horses) excel even with conformation faults.
Conformation of the 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.
Conformation of the shoulder, forearm, and chest.
The Shoulder.
Straight, upright, or vertical shoulder
Laid-back or sloping shoulder
The humerus (a.k.a. the arm bone)
The arm bone is from the point of shoulder to the elbow, it is covered in heavy muscle and serves as a leverage point for the muscle of the front leg attached near the elbow.
"Ideal"
Conformation of the Ideal Humerus (all measurements are while the horse is standing squarely)
Faults
"Too long humerus"
note "standing under" simply means that the horses legs are too far under his body and his chest sticks out.
"Short humerus"
note: that is the shoulder is too angled (less than 45 degrees) then the horse's front legs will be stilted and stiff.
The Elbow
Conformation
"Possible faults"
"Turned-in/tied-in elbow"
"Out-turned elbow"
The Forearm (radius).
Conformation
"Long forearm"
"Short forearm"
The Chest.
The conformation of the horse's chest plays a significant role in his level of endurance and stamina. A horse that will do work requiring speed, power, or endurance needs as much room as possible for maximum lung expansion. 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.
The thorax of the horse is flatter from side to side, as compared to the human thorax, which is flatter from back to front. The horses thorax is also deeper from the breastbone to the spine. This gives the horse a greater lung capacity, and thus greater endurance.
Conformation
Chest shape
When viewing the chest from the front, the chest should be wider at the bottom than at the top. The shoulder blades should be much closer together at their tops, toward their withers, than at the points of shoulders where the front legs attach.
Well-sprung ribs
Slab-sided ribs
Barrel chest and deep chest
"Chest faults"
Narrow chest
Too-wide chest
[All information is derived from "The horse Conformation Handbook" written by Heather Smith Thomas]
Narrow breast
Pigeon-breasted
Conformation of the body.
Withers.
Mutton withers
Hollow behind withers
High withers 
Back.
Long back 
Short back 
Saddle-, hollow-, low-, sway-backed/ down in the back 
Loin and coupling.
Roached back 
Long or weak loins/weak coupling 
Short –coupling
Rough coupling/widow's peak
Croup and "hip".
The croup is from the lumbosacral joint to the tail. The "hip" refers to the line running from the ilium (point of the hip) to the ischium (point of the buttock)of the pelvis. After the point that is made by the sacrum and lumbar vertebrae, the line following is referred to as the croup. While the two are linked in terms of length and musculature, the angle of the hip and croup do not necessarily correlate. But it is desirable for a horse to have a square to slightly pear shaped rump. A horse can have a relatively flat croup and a well-angled hip. Racehorses do well with hip angles of 20-30 degrees, trotting horses with 35 degrees. Once a horse is developed, the croup should be approximately the same height as the withers. In some breeds a high croup is hereditary trait.
Steep Croup or Goose Rump
Flat or Horizontal Croup
Short croup
Short "hip"
Flat "hip"
Jumper's Bump (also known as Hunter's or Racking Bump) 
Tail.
High Tail Set
Low Tail Set 
Wry Tail/ Tail Carried to One Side
Ribcage and flanks.
Wide Chest and Barrel/Rib Cage
Pear-Shaped Ribcage/Widens Toward Flank
Well-Sprung Ribs
Slab-Sided
Tucked Up/Herring-Gutted/Wasp-Waisted
Good Depth of Back
Conformation of the hindquarters and hips.
"The Hindquarters"
Short Hindquarters
Steep-Rumped
Goose-Rumped
Cat-Hammed/Frog's Thighs
Thighs
"The Hips"
Narrow Hips
Rafter Hips/Wide Hips
One Hip Bone Lower/Knocked-Down Hip
High Stifles/ Short Hip
Low Stifle/ Long Hip
Conformation of the front and hind legs.
"The Cannon and Tendons"
Long Cannon Bone 
Short Cannon Bone
Rotated Cannon Bone 
Bench or Offset Knees/ Offset Cannons
Tied-in Below the Knee
"The Front Legs- The Knee"
Medial Carpal Deviation/ Carpus Valgus/ Knock-Kneed 
Bucked, Sprung, or Goat Knees/ Over at the Knee 
Calf-Kneed/Back at the Knee 
"The Front Legs- The Fetlock"
Toed-Out/Lateral Deviation of Pastern from Fetlock/ Fetlock Valgus 
Toed-In/Medial Deviation of Pastern/Fetlock Varus
"The Hindlegs"
Short Gaskin/Hocks High
Long Gaskin/Low Hocks
Hocks Too Small
Cut Out Under the Hock
Camped Out Behind 
Sickle- or Sabre-Hocked/ Overangulated Long Hind Legs 
Post-Legged/Straight Behind
Bow-Legged/Wobbly Hocks
Cow Hocks/Medial Deviation of the Hocks/Tarsus Valgus
Conformation of the pasterns.
The angle of the pasterns is best at a moderate slope (between 50-55 degrees) and moderate length.
Pasterns Long and Sloping 
Pasterns Short and Upright 
Conformation of the feet and base.
The hooves bear all the weight of the horse. As each foot hits the ground, a concussive force passes through the foot up to the leg. The complex structure of the hoof is designed to absorb this impact, preventing injury. The internal hoof structure also aids circulation. When a horse is ridden, the weight of the rider adds to the force absorbed by the legs and feet. Poor conformation of the feet may lead to uneven or ineffective distribution of these impacts, in some cases increasing the risk of injury. Therefore, the hoof conformation is important to soundness.
Toe-Out/Splay Footed
Toe-In, Pigeon-Toed
Base Narrow in Front: Toed-Out or Toed-In
Base Wide in Front: Toed-In or Toed-Out
Stands Close Behind/Base Narrow Behind
"The Hoof"
Feet Too Small 
Feet Large and Flat/ Mushroom-Footed 
Mule Feet
Coon-Footed 
Club Foot 
Contracted Heels 
Thin Walls
Flared Hoof Wall 
Overall balance and bone.
Insufficient Bone
Light-Framed/Fine Boned 
Coarse-Boned/Sturdy-Framed 
Withers Higher than Croup 
Withers Lower than Croup/Rump High/Downhill Balance 
Too Tall or Too Short (in context to rider) 