Breyer models are sculpted, not simply to represent some abstract idea of physical perfection, but to represent real horses (many actually are modeled to resemble famous equines both past and present). No horse if free from some kind of physical imperfection. Conformation flaws are even found in champions of every breed. Good conformation is desirable trait, it is not an absolute indicator of what makes a "good" horse.
To have a discussion about breeds, it is more helpful to begin with the basics of good conformation. A horse’s conformation isn’t just a collection of physical traits that makes it more aesthetically pleasing to the eye, but often good conformation goes hand in hand with rideability. Correct conformation makes a horse less likely to suffer injury, breakdown or be unable to perform its "job" adequately and enables the horse to perform with maximum efficiency and ease.
To add complexity to the topic of conformation there are "fashions" within the horse breeding world. Such as a preference for ever-taller horses or flashy coloring, even in breeds which don’t normally display such extremes. There are also "fashions" within each breed, some of which have radically changed the look and/or use of a particular breed. Many breeds have decreased in quality due to the "fashion" of a single trait regardless of its merit to the breed's over all usefulness.
You may not know it, but the custom of breeds itself is a "fashion". At one time there was no such thing as a breed. All horses were classified into only a few general types depending on their use. Saddles were different then as well, the stirrups were longer and the cantle higher than on modern saddles. The rider’s knees were not bent and did nothing to absorb the shock of the horse's gait and posting was unknown. Anyone who has ever sat the trot knows how uncomfortable that can be, so for the most part, the trot was considered unrideable. Most people walked, cantered or galloped or, had horses that were taught to "amble" (The amble may have been pacing or some other kind of artificial gait.). If they were wealthy enough owned a Spanish jennet,which may have been a gaited type of horse.
Breeds developed in a region (many European breeds are named for the location in which the breed was developed) where horses were bred. Horse breeding was originally the pastime of the nobility.
The literature of many breed societies would like you believe that every individual of that breed carries all of the desired traits of that particular breed. This is not only misleading, but impossible. No two horses are exactly alike (just as no two people are exactly alike) even if they have the same sire and dam.
Much research has been done to uncover the mystery of the genetic code which determines coat color, but other than that and research into the hereditary diseases of horses, there is little information about what other physical or mental traits are dominant or determined mostly by the sire or mostly by the dam. The fact is, even if two physically perfect equine specimens were paired, the result is not guaranteed to be as perfect as either parent. This could be due to genetic variation or to differing methods of training or other unknown factors. There are also variable that effect the foal while its still in the womb, such as stress, illness or inadequate diet for the mare.
Breed specifics:
Though Man O’ War, Secretariat and Seabiscuit are all Thoroughbreds, each differs slightly in conformation. In some individuals the differences are slight, but others have differences that are quite significant. Yet, all of these horses are the same breed.
Taking the Thoroughbred as an example:
(The Encyclopedia of Horses and Ponies)
"In appearance, the Thoroughbred should have excellent conformation having a finely modeled head set onto an elegant and arched neck. The shoulder should be sloping with a defined wither and a short strong back. The (hind) quarters should be muscular with clean legs and low hocks."
That’s it. All of the physical characteristics Thoroughbreds should have in common, but what is to be done with a Thoroughbred model that does not (or any other model of a breed which does not conform well to its breed characteristics or actually displays undesired traits of that breed). Maybe (in the case of models of common breeds like the Thoroughbred) you don’t want to show your model in crowded classes where he/she will be ignored.
The first thing you need is more than a single reference book ofhorse breeds. One book is not enough, even though it may have all of the world’s breeds in it. Most books of this kind only have one picture example of each breed; more books mean more examples and a more realistic idea of what this breed really looks like. The most helpful books go into detail as to the history and origins of breeds, typical coat coloration of each breed and the notable physical traits of each breed. The Internet is also a good place to look for examples of a particular breed. Ideally, you want to find a picture which most closely matches your model in physical traits and color. (For certain breeds, pictures of exotic colors, such as gruella, albino, liver chestnut with a flaxen mane and tail or pinto might be more difficult to find as they are exceedingly rare, so you may have to settle for an example of one or the other.)
Good conformation:
Keep in mind that all domestic horses were originally bred with for specific use and though today those differ from uses in the past, horses still need the physical conformation that makes them most useful and successful. These general guidelines for good conformation apply to every breed of domestic horse.
The head: Of course, the size of the head needs to be in proportion to the body no matter the breed. Some breeds (draft and pony breeds in particular) are known for a tendency toward large heads. The adding of Arabian blood to many breeds has added to the refinement of that breed and improvement of the proportion and shape of the head.
When you take a close look at the head of this Thoroughbred model, you can't help notice certain characteristics also found in the Arabian breed: Large eyes, fine skin, a tight muzzle and finely shaped ears. Other characteristics: Large nostrils, a slightly convex profile on the bridge of the nose, is more typical of Thoroughbreds and other European breeds. Though this model depicts a Thoroughbred, it also could be shown as an Anglo-Arab. It is not uncommon for Thoroughbreds to display certain Arabian characteristics as Oriental blood (That is horse breeds from the regions of the Middle East and China) was used in the development of the Thoroughbred breed.
The head of this Thoroughbred model of a shows a lesser degree of refinement than the previous example. Like the head of the previous example, the muzzle of this horse is tight, its eyes are large and the ears are delicate, though the head is shorter, more snub and with a slightly more pronounced convex profile, which is more common in breeds of European origin.