What Fuels Performance at the Kentucky Derby

As the Kentucky Derby nears, Churchill Downs is once again the center of global attention. Beyond the spectacle and long-standing tradition lies a deeper focus: the physical and biological makeup of the thoroughbred horse. With years of selective breeding, rigorous training, and scientific observation, these animals reflect a complex combination of strength, stamina, and instinct.

On a cool morning in Louisville, the sound of hooves striking the dirt track breaks the quiet as thoroughbreds pass in quick succession. From a raised vantage point, Dr. Will Farmer, equine medical director at Churchill Downs Inc., observes their pace. “They’ve always had to run, it’s how they survived,” he said. Horses, as prey animals, developed this ability as a means of staying alive. That same characteristic plays a major role in how they move today.

Contemporary identifies Cardiff ties thus far with trainers and breeders connected to the Kentucky Derby for decades. According to them, all athletic ability is chalked up to the heart and lungs. The Kentucky Derby horses almost always have hearts of extraordinary size, exceeding 20 pounds in weight, as in the case of Secretariat. Such large hearts facilitate speedy blood circulation so necessary in a race run at such breakneck speed as the Kentucky Derby. With these lungs that can take up to 60 liters of air, the entire system is suited to providing for the sheer physical demand placed by the Kentucky Derby and similar top-notch events.

The advantage doesn’t stop there. Horses can also store red blood cells in their spleens and release them during physical stress. Dr. Hilary Clayton explains that adrenaline triggers this release, improving oxygen delivery right when it’s needed most. She compares this natural response to blood doping ,  though in this case, it’s built-in.

From a structural standpoint, horses are equipped for speed. Long, thin legs act like levers. Their tendons and ligaments function like springs, helping them push forward with each stride. Strong hindquarters assist in driving that movement. Dr. Farmer notes that these are common characteristics among large prey animals, all adapted for running over long distances.

The brain also plays a role. Although their frontal lobes are smaller compared to those of humans, horses are quick to react and often show an eagerness to move. Dr. Scott Bailey of Claiborne Farm believes this responsiveness contributes significantly during races. “They’re able to stay focused and engaged without hesitation,” he said.

While these traits support performance, they also come with risks. Thin legs must absorb the force of repeated impact, especially on tracks where speed is pushed to the limit. Over time, stress injuries can occur. This issue gained widespread attention in 2023 when 12 horses died at Churchill Downs during a single season. The incident raised questions about safety and prompted changes across the industry.

In response, Churchill Downs updated the dirt surface and brought in a dedicated safety veterinarian. The Horseracing Integrity and Safety Authority also introduced stricter race-day checks and uniform medication guidelines. Their 2024 report showed a 27% reduction in race-related deaths at accredited tracks, a sign that the new measures are having an effect.

Still, the question remains: what separates an average racer from a top contender? Genetics, environment, and consistent training all contribute,  but there is no simple formula. “People try to find that perfect mix of parentage and conditioning,” Bailey said. “But no one really knows what sets a winning horse apart.”

Farmer agrees. While elite breeding helps, champions have also come from modest backgrounds. “Some of the most memorable winners weren’t the most expensive horses at the sale,” he said. “They just had the right mix of health, timing, and will to compete.”

As Churchill Downs prepares for another Kentucky Derby, attention will be on more than just who crosses the finish line first. Each horse on the track reflects generations of human-animal partnership and the ongoing study of how nature and training influence athletic achievement.