First Published in the Trainer Magazine, Breeder's Cup Edition

In an industry that often comes down to the wire, understanding a horse’s performance strengths and weaknesses is crucial when planning their training regimen. Training Thoroughbreds isn’t a one-size-fits-all endeavor—factors like racing age, track distance, and surface type are just a few of the things we have to consider. Over the years, advances in veterinary care, nutrition, and conditioning have shaped the sport, helping us to produce more competitive horses. But imagine tailoring your training plan based on DNA—not just intuition. Now, there's an increasing emphasis on a promising tool that enables you to do just that: performance genetics - the ability to shape training, feed, care and success using a horse’s most basic code.

It isn’t just scientists who feel that equine genetics can change the way we understand horse racing. California Horse Racing Board Vice Chairman Oscar Gonzales said, “California breeding is at a crossroads—if we want to produce top-quality horses, we must embrace new technologies and analytics. By using information from Thoroughbred DNA, we can make better breeding and training decisions that promote health and soundness, ensuring the best horses reach the track. Other sports are using tech to elevate their game, and so should we.”

By understanding a horse’s genetic makeup, trainers can fine-tune both their training programs and racing strategies. In this article, we will explore how key genetic markers—including the myostatin gene (MSTN), height and respiratory health, temperament, and genomic inbreeding values—can influence training, optimize performance, and ultimately increase strike rates while decreasing public tragedy.

Race Length Suitability

Performance genetics aren’t entirely new to the Thoroughbred world. For years, breeders and trainers have been using the “speed” gene, MSTN, to help determine a horse’s optimal racing distance. But how does this gene really affect performance, and why is it an important component for training?

Myostatin is a protein that plays a crucial role in the negative regulation of muscle mass, particularly the balance between fast and slow-twitch muscle fibers. Genetically, horses can have two copies of the “Sprint” variant, two copies of the “Endurance” variant, or one copy of each—known as “Sprint/Endurance” also called “Mid-Distance.”

Sprint-type horses are typically more muscular and compact, equipped with a higher proportion of fast-twitch muscles that enable explosive bursts of speed over shorter distances. These horses generally excel in races under 6 furlongs, physically mature faster, and often earn more as two-year-olds.¹ Therefore, focusing on high-intensity, short-duration training that sharpens acceleration, and avoiding endurance-building exercises that play against the horse’s natural abilities, may help maximize their potential.

In contrast, endurance-type horses possess a greater percentage of slow-twitch muscle fibers, which contract more slowly but can sustain effort without fatiguing quickly. Typically appearing more refined/smaller and less muscular, these horses may reach their peak performance later in life than their sprint-type counterparts, which should be taken into consideration when planning a racing career. They are particularly well-suited for longer races, typically 9 furlongs or more, and incorporating aerobic conditioning exercises into their training regimen may be beneficial to capitalize on their genetic predisposition for sustained effort.

Sprint/endurance horses are versatile, having both abilities, and can perform well across a range of distances, benefiting from both speed and stamina. Therefore, their training might include exercises tailored for both short and long distance, depending on the long-term goals for that particular horse.

Incorporating MSTN testing into a training program enables more precise conditioning based on a horse’s genetic muscle makeup, ultimately reducing the risk of over-training and increasing performance consistency. However, it’s essential to consider many other physical traits with genetic factors, such as height (LCORL) and health; all which come into play.

Connecting Height and “Roaring”

When selecting mating pairs for Thoroughbreds, it’s common practice to evaluate physical traits alongside pedigree. Breeders often seek attributes like increased body size and muscle mass, aiming to produce bigger, faster, and stronger horses. Yet, it’s important to note that larger horses physically mature at a slower rate compared to those of average height. Furthermore, research indicates that horses carrying at least one copy of LCORL may be taller or larger but are also at a higher risk of developing Recurrent Laryngeal Neuropathy (RLN), commonly known as “roaring.”²

Roaring is a disease that results in a paralyzed larynx and ultimately leads to an obstruction of airflow during intense exercise. Horses with RLN struggle to breathe normally at speed, therefore their performance potential could be limited.

In addition to height, several other factors can contribute to a horse’s predisposition to RLN. Fortunately, genetic tests are available to determine a horse’s risk level: ~12x higher risk (RLN/RLN), ~5x higher risk (RLN/n), or has no increased risk (n/n) for developing the disease.

It’s important to realize that knowledge is power. By understanding the genetic risks associated with your horse, you can anticipate physical limitations and adjust training accordingly. This may involve incorporating more respiratory conditioning, closely monitoring oxygen intake under stress, or considering surgical intervention for affected horses.

Managing the Mind

Performance is not just about physicality—temperament plays a crucial role in how a horse handles the demands of training and competition. As more research is done with the assistance of Thoroughbred trainers, we can use genetic analysis to provide insights into a horse’s behavioral tendencies. In this case, let’s look at the temperament gene, DRD4, which tells us whether the hose is more “Curious,” “Vigilant,” or a combination of both.³

Curious horses, defined by a willingness to be interested in or approach novel objects, are often more inclined to engage with new environments, challenges, or stimuli. This means they may be more adaptable to varied training regimes, allowing them to learn faster in new situations or settings, such as different tracks or training facilities.

That is not to say Thoroughbreds who are vigilant about their surroundings do not readily learn or adapt, only that they may benefit from different training methods. These horses often possess heightened awareness of their surroundings, making them valuable assets in racing. This trait may mean they respond more readily to jockey commands and can navigate environmental factors, such as the positioning of other horses, while racing. It's essential to recognize that temperament cannot be attributed to a single gene; other factors, such as environment and stress, also play a significant role in shaping behavior. For instance, more high-strung horses may need additional mental conditioning to cope with the pressures of race day, including exposure to noise and distractions. In contrast, calmer horses might benefit from a more stimulating environment to maintain their focus and sharpness. Trainers can leverage this knowledge to adjust everything from a horse’s daily routine to its training regimen, ensuring that the animal's psychological needs are addressed in a way that enhances performance.

Balancing Talent and Risk

Another critical component of performance genetics is understanding the genomic inbreeding value (GIV). Inbreeding in Thoroughbreds is a double-edged sword—it can amplify desirable traits, but it can also increase the risk of hereditary health issues that negatively impact performance. While more research is needed, these issues may present as lower endurance, slower recovery times, or reduced competitiveness on the racetrack.

Over the past five decades, inbreeding rates have increased significantly, yet we have not observed a corresponding rise in the speed of Thoroughbred horses.⁴ ⁵ In fact, a 10% increase in inbreeding reduces a horse’s likelihood of successful racing by 7%, but what does this mean for performance?

Horses with a high inbreeding coefficient are often more susceptible to injuries and genetic disorders, leading to declines in overall vitality and performance. By understanding a horse's GIV, trainers can refine their conditioning programs to emphasize injury prevention and overall health management. For example, you may consider implementing medical screenings or adopting less aggressive workout routines to minimize the risk of breakdowns related to structural weaknesses.

Conversely, horses with lower inbreeding values tend to have greater genetic diversity, which can enhance their resilience and adaptability. These horses may be able to manage more intense training schedules without the same risk of injury, allowing trainers to push them harder when necessary.

Conclusion: Utilizing Performance Genetics

In Thoroughbred racing, there is no universal training program, nor is there a guaranteed formula for ensuring your horse becomes a champion. However, by leveraging performance genetics, we can increase those odds and refine training strategies in ways that were previously unimaginable.

By understanding key genetic markers such as the MSTN gene, and the connections between height, maturation and respiratory risk, trainers can tailor their methods to meet the unique needs of each horse. Taking into consideration the horse’s temperament and genomic inbreeding value allows for further refinement.

Rocky Savio, Partner and head of track performance for Savio Cannon Thoroughbreds, said, "DNA testing not only helps reduce hereditary disease but also allows for the optimization of breeding and training strategies, leading to stronger, faster, and more resilient horses on the racetrack.” Savio and Cannon’s deep understanding of these strategies is evident in their home-bred stallion, Smooth Like Strait, who achieved remarkable success with six stakes race wins before retiring sound to stand at War Horse Place.

As the science of equine genomics continues to evolve, owners and trainers that incorporate these performance factors into their training programs will be at a distinct advantage—giving their horses the best possible chance to reach the winner’s circle. Performance genetics provide a profound edge, and with the precision of modern DNA analysis, the future of Thoroughbred training is shaping up to be faster, stronger, and smarter than ever before.

Read More at The Trainer Magazine's Breeder's Cup Edition

References

¹ Tozaki, T., Sato, F., Hill, E. M., Miyake, T., Endo, Y., Kakoi, H., Gawahara, H., Hirota, K., Nakano, Y., Nambo, Y., & Kurosawa, M. (2011b). Sequence variants at the myostatin gene locus influence the body composition of Thoroughbred horses. Journal of Veterinary Medical Science, 73(12), 1617-1624.

² Boyko, A. R., Brooks, S. A., Behan-Braman, A., et al. (2014). Genomic analysis establishes correlation between growth and laryngeal neuropathy in Thoroughbreds. BMC Genomics, 15, 259. https://doi.org/10.1186/1471-2164-15-259

³ Momozawa, Y., et al. (2005). Association between equine temperament and polymorphisms in the dopamine D4 receptor gene. Mammalian Genome, 16, 538-544. PMID: 16151699

⁴ Hill, E. W., Stoffel, M. A., McGivney, B. A., MacHugh, D. E., & Pemberton, J. M. (2022). Inbreeding depression and the probability of racing in the Thoroughbred horse. Proceedings of the Royal Society B, 289, 20220487. http://doi.org/10.1098/rspb.2022.0487

⁵ McGivney, B. A., Han, H., Corduff, L. R., et al. (2020). Genomic inbreeding trends, influential sire lines, and selection in the global Thoroughbred horse population. Scientific Reports, 10, 466. https://doi.org/10.1038/s41598-019-57389-5