Horse breeding is the process by which humans interfere in equine reproduction to produce an offspring that has certain desired qualities. Over time horse breeding has produced breed or phenotypes in horses; it has also benefited the domestic horse whose chances of a successful conception, gestation and foaling are improved by selective mating.
It is known that horses were domesticated around 4,500 BCE but the origins of horse breeding are less clear. The first documentation of horse breeding is seen in the records of the Bedouin tribes of the Middle East. Their pedigrees of Arabian horses are dated 1330 AD but it can be assumed that the breeding of these horses took place for some time before they were written down. Breeding is also known to have taken place for thousands of years in western central Asia where the Akhal-Teke was developed, and in the nomadic Mongolian steppe tribes.
Equine breeding has always been dictated by the use the horses were to be put to and the environment they were born into as can been seen in a more close look at historical breeding. In medieval Europe horses were heavy and thick coated, bred for farming, war, cold climates and movement in relatively small areas. On farms these horses pulled loads, plows and wagons, and were bred for size and power. Warhorses were called destiers and are the ancestors of our present day heavy coldbloods. Their size gave them the strength to carry a knight in full armor and the force to drive a lance in war, these horses were powerful weapons.
In contrast to European horses, Asian horses were bred for speed and agility. Muslim warriors in Africa and the Middle East and Bedouin tribes conducted war through raids and it was important for their horses to be able to out maneuver the enemy. The Arabian horses of the Middle East were also very well adapted to their vast dry land and hot climate which can be seen in their endurance, and speed. Later, as Europeans began to explore and crusade, Arabians and other Asian horses including Barbs were "outcrossed" with European horses to create more agile and faster warhorses and messenger horses.
During the Renaissance the risen state of the nobility gave birth to the haute ecole style of riding in which fancy athletic movement was the ideal. In this age horses were further refined for dexterity and structure, distinctive of this time is the Lipizzaner which to this day is known for its characteristic stylized and movement.
In the late 1600s in England the Thoroughbred was developed for racing. These horses were sired by three foundation Arabian stallions and to this day every purebred Thoroughbred can be traced back to those three stallions. Thoroughbreds remain the ideal racing horse today. Also in the 17 and 18 centuries the warmblood was developed in Europe for pulling carriages. These horses had a size and strength that allowed them to pull heavy loads but were more refined than the draft horses of earlier times.
The industrial revolution negated the need for horses industrially and most draft horses are now seen only in competitions and rarely on working farms. Warmbloods have been outcrossed with Thoroughbreds to produce sport horses for competition and leisure and these warmblood mixes of draft horses and thoroughbreds have produced the breeds that are now seen in competitive showing. As a side note there are still a large number of breeds that were adapted to certain work and are still bred today. Included in these is the American Quarter Horse (originally used in ¼ mile races and western events), ponies originally bred for mine work, and other specialized breeds.
In breeding horses the dam (mother) and the sire (father) are equally genetically important - each contributes 50% of the foals genes. However there is some question as to the real impact of each parent, the sire can have more impact on the breed as he can sire many foals, however the dam has more impact on the individual foal as her temperament and habits form the foals personality during early life.
When choosing to breed, mares and stallions must be looked at in conjunction. Horses are judged by their bloodlines, temperament, conformation, performance record, and health. All of these elements are believed to be inherited by offspring. In looking at bloodlines it is important to check historical records, certain bloodlines have worked more successfully with others. Temperament must be considered in order to judge a foal's fitness for a certain discipline, in a racehorse aggression could work to an advantage, while for a child's recreational pony docility would be important. Conformation (the horses' physical structure) is strongly inheritable and it is important that horses' complementary conformation is taken into consideration in breeding. In sires performance success in a certain discipline is crucial as foals seem to inherit their sire's performance abilities. Also a sire's other offspring can be considered with regards to a foals probable abilities. For mares health is a special concern as stud fees make it important for a pregnancy to be successful and it can be detrimental to a mare's well being to abort a pregnancy.
In the wild mares mate and foal in late spring, domestically, horses destined for competition are mated as close to January 1st as possible so that they will have size and maturity advantage in competition with horses of their age. Horses come into estrus about once a month in spring and summer, and in order to stimulate early estrus stalls are lit to simulate longer daylight. Once in estrus a mare is brought into the presence of a stallion where she will urinate and raise her tail showing her vulva. The stallion will then approach with a high head, nickering, nipping, nudging and smelling her.
There are two different ways of "covering" a mare. These are called live cover and artificial insemination. In live cover a mare is brought to a stud farm where the stallion will mount her. AI is a less stressful way to mate horses and it is safer than live cover - incurring less damage from wound up horses. It also allows for international breeding and breeding from studs that may not be able to mount a mare. Despite said pros of AI Thoroughbreds must be conceived through live cover in order to be registered. Surrogate dams, and embryo transfers are also possible in conception for mares whose bloodlines and conformation are desirable but who are not able to carry a foal.
If the mare becomes pregnant, she will bear a foal after a gestation period of 11 months. She is in labor for about thirty minutes; the baby stands within ½ hour and nurses immediately. After 4 - 8 months the foal is weaned and begins the training that will bear out the success of its breeding and begin to shape its possible future as a broodmare or stud stallion.
Horse breeding is a product of human history and environment and it is through the manipulation of equine reproduction that we now have the hundreds of special horse breeds that we see around us today. Though horses are no longer important in industry or economy I hope that individuals will continue to breed them for sport and leisure so as to maintain and develop the breeds, continuing in an age old tradition.