Published on: October 2, 2024
Thoroughbreds are bred for speed. But what makes one faster than another? As a Thoroughbred owner with over 25 years of experience buying, selling, and racing these incredible animals, I’ve learned that the answer lies in their genes. Understanding these genetic factors can help breeders, owners, and even bettors make more informed decisions.
In this article, we’ll explore the science behind Thoroughbred speed, examining the genetic factors contributing to their athleticism and the modern breeding practices used to create champions. We’ll also examine the ethical considerations and future implications of genetic enhancement in the Thoroughbred industry.

The Genetic Foundations of Speed
Understanding Thoroughbred genetics is crucial for breeders who aim to produce horses with exceptional speed and stamina. Thoroughbreds are renowned for their speed, a trait deeply ingrained in their genetic makeup. But what specific genes and genetic factors contribute to this remarkable athleticism?
The Speed Gene (MSTN): One of the most significant discoveries in Thoroughbred genetics is identifying the “speed gene,” officially known as myostatin (MSTN). This gene plays a crucial role in regulating muscle growth and development. Variations in the MSTN gene can influence a horse’s muscle fiber type composition, affecting its speed and stamina.

Research from the University of Kentucky has shown that certain variations of the MSTN gene are associated with sprinting ability, while others are linked to stamina for longer distances. You can read more about this research here: Gluck Research Center. This discovery has revolutionized Thoroughbred breeding, allowing breeders to make more informed decisions based on a horse’s genetic potential.
Mitochondrial DNA (mtDNA): Another critical factor in Thoroughbred speed is mitochondrial DNA (mtDNA), which is passed down exclusively from the mother (dam). Mitochondria are the powerhouses of cells responsible for energy production. Variations in mtDNA can affect a horse’s energy metabolism and, consequently, its athletic performance.
A study published in the journal Mitochondrion found that specific mtDNA haplotypes (groups of genes inherited together) are associated with increased racing performance in Thoroughbreds. You can access the complete study here: Mitochondrial DNA: an important female contribution to thoroughbred racehorse performance. This research highlights the importance of considering the dam’s genetic contribution when breeding for speed.

Modern Thoroughbred Genetics and Breeding Practices
Modern Thoroughbred breeding combines art and science, combining traditional knowledge with cutting-edge genetic technologies. Here are some key practices used to enhance speed and athletic performance:
- Pedigree Analysis: Analyzing a horse’s pedigree, including its ancestors’ racing performance and genetic background, is crucial for identifying potential strengths and weaknesses. Breeders often focus on bloodlines known for producing fast and successful racehorses. Resources like the Jockey Club’s online pedigree database can be invaluable tools for this analysis.
- Genetic Testing: Advancements in genetic testing have revolutionized pedigree analysis and breeding decisions. Tests for specific genes, like the myostatin (MSTN) gene, can provide insights into a horse’s potential for speed and stamina. Certain variations of the MSTN gene are associated with sprinting ability, while others are linked to stamina for longer distances. However, it’s important to use this information responsibly and ethically, considering the potential impact on the breed’s genetic diversity and the welfare of the horses. For example, the Equine Genetic Diversity Test offered by the University of California, Davis, can help assess a horse’s genetic diversity and potential for athleticism.
- Conformation Evaluation: A horse’s physical structure, or conformation, plays a significant role in its athletic ability. Breeders assess factors like leg length, muscle definition, and overall balance to identify horses with the physical attributes conducive to speed. The American Association of Equine Practitioners (AAEP) provides resources on equine conformation and its relationship to performance.
- Performance Testing: Evaluating a horse’s performance through trials or races provides valuable insights into its speed and athletic potential. This information, combined with pedigree analysis and genetic testing, can be used to make informed breeding decisions.
Real-World Examples:
- Speed Gene Test and “Galileo Gold”: The Speed Gene test analyzes variations in the MSTN gene to predict a horse’s optimal racing distance. “Galileo Gold,” a champion miler, highlighted the complexity of genetic influences and the importance of considering other factors beyond genetics.
- Genomic Selection and “American Pharoah”: While not directly used in breeding “American Pharoah,” his success sparked interest in using genomics to identify future champions. His pedigree and performance data have been analyzed to identify potential genetic markers associated with his exceptional speed.
- Breeding Operations: Many leading Thoroughbred breeding operations, like Coolmore Stud, incorporate genetic testing to inform breeding decisions and optimize the chances of producing high-performing racehorses.
- Genetic Testing for Inherited Diseases: Genetic testing helps identify carriers of inherited diseases, enabling breeders to make informed decisions. For example, the University of California, Davis, offers a test for Hyperkalemic Periodic Paralysis (HYPP), a muscle disorder that can affect performance.

Ethical Considerations in Genetic Enhancement
As genetic technologies advance, it’s essential to consider the ethical implications of genetic enhancement in Thoroughbred breeding. Key concerns include:
- Maintaining Genetic Diversity: Overemphasis on specific genetic traits could reduce genetic diversity, potentially making the breed more susceptible to disease or limiting its adaptability. The Thoroughbred Breeders’ Association (TBA) emphasizes the importance of maintaining genetic diversity in its breeding guidelines.
- Example: A study by the University of Dublin’s School of Veterinary Medicine found that the Thoroughbred population has experienced a decline in genetic diversity over the past century, raising concerns about the long-term health of the breed.
- Animal Welfare: Breeding practices must prioritize the health and well-being of the horses, avoiding any practices that could compromise their welfare. Organizations like the American Horse Council advocate for responsible breeding practices that prioritize equine welfare.
- Example: Concerns have been raised about the potential for genetic enhancement technologies to increase the risk of injuries or health problems in racehorses if not used responsibly.
- Fairness in Competition: Genetic enhancement technologies raise questions about fairness in competition. Regulations and guidelines may be necessary to ensure a level playing field. The Racing Medication and Testing Consortium (RMTC) is involved in discussions regarding regulating genetic enhancement in horse racing.
- Example: If some horses are genetically enhanced for speed, it could create an unfair advantage for those owners and breeders with access to such technologies.
By carefully considering these ethical implications and engaging in open dialogue, the Thoroughbred industry can harness the power of genetic technologies while upholding the integrity of the breed and the sport.

Frequently Asked Questions about Thoroughbred Genetics
What is the “speed gene”?
The “speed gene” refers to variations in the myostatin (MSTN) gene that can influence a horse’s muscle fiber type composition and affect its speed and stamina.
How is genetic testing used in Thoroughbred breeding?
Genetic testing is used to identify potential for speed and stamina, assess the risk of inherited diseases, and make more informed breeding decisions.
What are the ethical concerns surrounding genetic enhancement in Thoroughbreds?
Ethical concerns include maintaining genetic diversity, ensuring animal welfare, and preserving fairness in competition.
What is the future of Thoroughbred breeding?
The future likely involves a balanced approach that combines traditional knowledge with cutting-edge genetic technologies, such as genomic selection.
Conclusion: The Future of Thoroughbred Breeding
The implications of Thoroughbred genetics research extend beyond the racetrack, potentially contributing to advancements in equine health and performance across all disciplines.
The future of Thoroughbred breeding lies in a balanced approach that combines the best of traditional knowledge with cutting-edge genetic technologies. This means integrating time-tested practices like pedigree analysis and conformation evaluation with modern tools like genetic testing and performance data analysis.
One example of this integrated approach is the increasing use of genomic selection. This technique uses DNA markers to predict a horse’s genetic potential for racing performance, allowing breeders to make more informed decisions about mating pairs. The Thoroughbred Owners and Breeders Association (TOBA) provides resources on genomic selection and its potential benefits for the industry.
However, the future of Thoroughbred breeding also faces challenges. Maintaining genetic diversity within the breed ensures its long-term health and adaptability. Overemphasis on specific genetic traits could reduce diversity, making the population more susceptible to disease.
Another challenge is ensuring the ethical use of genetic technologies. It’s essential to prioritize the welfare of the horses and avoid practices that could compromise their well-being. The International Federation of Horseracing Authorities (IFHA) has published guidelines on using genetic technologies in horse breeding, emphasizing the importance of ethical considerations.
Looking ahead, the Thoroughbred industry must continue to adapt and innovate. This includes embracing new technologies, promoting responsible breeding practices, and fostering collaboration between researchers, breeders, and racing authorities. By doing so, the industry can ensure a bright future for the Thoroughbred breed, producing exceptional athletes while safeguarding their health and welfare for generations.
Genetic technologies are rapidly changing the landscape of Thoroughbred breeding. What ethical considerations do you think are most important? How do you think these technologies will shape the future of the breed? Share your insights and join the conversation below!