Thoroughbreds Inherit Their Speed from a Handful of Ancestors

The horse, one of the world's fastest land animals, can gallop up to 40 miles (64 kilometres) per hour, a breathtaking pace compared to a human runner. This speed has made horse racing a beloved sport globally. The finest racehorses possess long legs and powerful muscles, traits that evolved in the wild to help horses escape predators and travel long distances in search of food. Over time, breeders selected the longest and leanest horses to develop racing breeds known for their sleekness, slenderness, and swiftness.

Genetic Legacy of Thoroughbred Horses

A recent genetic study of thoroughbred horses indicates that their exceptional sprinting capabilities can be traced back to a few key ancestors. The research points to a speed-related genetic variant that emerged from a single mare in the mid-17th century. This variant became prevalent in modern thoroughbreds, largely due to the Nearctic, a stallion who sired the most prolific breeding stallion of contemporary times.

Emmeline Hill, a genomics scientist at University College Dublin, noted that the evolution of racing practices since the Thoroughbred's inception has impacted the distribution of 'speed gene' types across various racing regions and periods.

Historical Roots and Founding Fathers

Thoroughbred horses, known for their strength, long legs, and sensitivity, are the most prestigious racehorses today. The breed originated in England in the 1700s after three legendary stallions—Darley Arabian, Godolphin Barb, and Byerley Turk—were brought to Europe from North Africa and the Near East. All thoroughbreds are descended from these "foundation sires."

Interesting Fact: The Darley Arabian, one of the foundation sires, was purchased for a mere 300 gold coins and went on to sire 100% of the male-line thoroughbred population.

Historical Moment: Eclipse, a legendary racehorse born in 1764, was so dominant in his races that he often finished far ahead of his competitors, giving rise to the phrase "Eclipse first and the rest nowhere."

The Science of Speed: The MSTN Gene

In 2010, Hill and her colleagues discovered how variations in the genetic code of Thoroughbreds influence their speed. A gene called MSTN, associated with muscle growth, comes in two alleles: C and T. Horses with two C alleles are fast sprinters, those with one C and one T allele are strong middle-distance runners, and T/T horses have less speed but greater stamina.

The researchers traced the history of these alleles to understand their origins and spread as breeders' demands changed. They found that the C allele was absent in distant horse relatives like zebras, indicating that the stamina-bestowing T allele was common in ancestral wild horses. This makes sense as wild horses needed stamina for long-distance travel.

Interesting Fact: The thoroughbred breed has remained genetically closed since 1791, meaning all thoroughbreds today can trace their lineage back to the three foundation sires without any external breeding.

Modern Breeding and the Influence of Northern Dancer

The widespread presence of the C allele in modern thoroughbreds was further examined by analysing the pedigrees of elite-performing horses. The data pointed to Nearctic, a horse born in 1954, as a significant contributor. Nearctic, sired by the renowned stallion Nearco, produced Northern Dancer in 1961.

Northern Dancer had an impressive racing career, winning 14 of 18 races and never finishing lower than third. After retiring, he became the most influential stud horse of his era. In the 1980s, breeding with Northern Dancer cost $1 million, allowing the C allele to spread widely among Thoroughbreds.

Interesting Fact: Northern Dancer's offspring have dominated the world's leading races, including the Kentucky Derby, the Epsom Derby, and the Prix de l'Arc de Triomphe.

Environmental Factors and Training

British scientists have been studying the DNA of successful thoroughbreds, including the champion racehorse Eclipse, who never lost a race after being born in 1764. Genetics play a significant role in a horse's success, but factors such as the environment, diet, training, and the jockey are also crucial.

Interesting Fact: The famous thoroughbred, Secretariat, who won the Triple Crown in 1973, had a heart that was nearly three times the size of an average horse's heart, contributing to his incredible stamina and speed.

The Future of Thoroughbred Breeding

The study highlights how racing trends influence the genetics of racehorses. Hill noted that breeders have significant power to shape the genetic makeup of their horses, with decisions about race patterns and commercial demands rapidly affecting the population's genetics.

Hill co-founded Equinome, a company that tests for the C and T alleles to determine the optimal racing distances for Thoroughbreds. This genetic trait has significant financial implications for breeders and owners. For example, Northern Dancer's 635 registered foals earned over $26 million by the time of his death in 1990.

Interesting Fact: The Kentucky Derby, one of the most prestigious horse races, was first held in 1875 and has been run every year since, making it the oldest continuously held sporting event in the United States.

Conclusion

From their evolutionary roots to their genetic advancements, thoroughbred horses have captured the fascination of breeders and racing enthusiasts alike. The blend of speed, stamina, and strategic breeding has created a legacy that continues to evolve with each generation, influenced by both scientific discovery and the ever-changing demands of the racing industry.