The Thoroughbred is a horse known for its speed and athleticism in horse racing. Its development stems from a deliberate and extensively recorded selective breeding initiative conducted in 17th and 18th century England. Breeders aimed to create a horse capable of sustained speed over distance, which transformed the burgeoning sport of racing. This process laid the groundwork for the modern Thoroughbred, influencing equestrian sports globally.
The Three Foundation Sires
Modern Thoroughbreds trace their ancestry to three specific stallions imported into England during the late 17th and early 18th centuries. These “foundation sires” were Oriental horses, primarily of Arabian, Barb, and Turkoman breeding, chosen for their inherent speed and stamina. Their introduction marked a significant turning point in horse breeding, as they were crossbred with native English mares to produce faster, more agile offspring.
The Byerley Turk, foaled around 1680, is believed to have been captured by Captain Robert Byerley at the Battle of Buda. He served as Byerley’s war horse, accompanying him during military service in Ireland, including the Battle of the Boyne in 1689. This stallion’s line was preserved through his great-great-grandson, Herod, who became a prominent sire in Thoroughbred history.
The Darley Arabian, foaled around 1700, was a bay Arabian horse purchased by Thomas Darley in Aleppo, Syria, in 1704. Darley shipped the stallion back to Aldby Park in England as a gift for his brother. Though standing at approximately 15 hands, his striking appearance and genetic influence were notable, with some studies suggesting that 95% of male Thoroughbreds trace their male line to him.
The Godolphin Arabian, sometimes referred to as the Godolphin Barb, was foaled in Yemen around 1724. His journey to England involved passing through several owners, including a period in France where he was given to King Louis XV. He was named after his best-known owner, Francis Godolphin, 2nd Earl of Godolphin, and his male line was preserved through his grandson, Matchem.
The Royal Mares
The development of the Thoroughbred involved more than just the imported foundation sires; the mares they were bred to were equally significant. These were not random horses but a collection of approximately 100 foundation mares, many of which were native British stock. Breeds like the Galloway and Irish Hobby, known for their hardiness and racing ability, contributed to this group.
Some of these mares also possessed earlier Barb, Turk, or Arabian lineage, indicating a history of selective breeding for desirable traits. The selection process for these mares was deliberate, focusing on their proven speed, stamina, and overall racing ability. This careful pairing ensured that the resulting offspring combined the imported speed of the sires with the established resilience and racing prowess of local stock, forming the basis of the new breed.
Establishment of the General Stud Book
The formalization of the Thoroughbred breed culminated with the establishment of a comprehensive breed registry, known as a stud book. James Weatherby undertook the meticulous task of compiling the pedigrees of these early horses, publishing the first volume of the General Stud Book in 1791. This publication listed the ancestry records of 387 mares, each traceable back to one of the three foundation sires or their immediate descendants.
The General Stud Book established a closed registry, which meant that to be officially recognized as a Thoroughbred, a horse’s lineage had to be verifiable through the entries in its earliest volumes. This act was crucial in cementing the Thoroughbred as a distinct and official breed, preventing outcrossing with other breeds and preserving the integrity of its unique bloodlines. The ongoing publication of the General Stud Book continues to maintain the purity and documented ancestry of Thoroughbreds worldwide.