For years the Thoroughbred industry has debated why racing fields are smaller, inventories thinner, and the overall horse population available for racing is down.
The most common explanations are familiar: a reduced foal crop, rising ownership costs, regulatory pressure, or the belief that horses are being pushed too hard too early. While each of these factors plays a role, none fully explains the depth or persistence of the problem. The core issue is not simply how many horses are bred. It is how many remain physically viable long enough to sustain a racing career.
According to statistics compiled by The Jockey Club, about 42% (The Jockey Club Fact Book, looking at foal crop years 2020-2022) of a registered foal crop will make a start at age 2. That figure often is interpreted as evidence of delayed development or conservative training, but it masks a more consequential factor. Roughly half of the remaining 58% eventually will race at an older age. The other half of that unraced-at-2 group—approximately 29% of the entire foal crop—will never make a single start.
That attrition occurs before economics, purse structure, or regulatory pressure come into play. These horses exit the system quietly during training due to physical limitations, soundness issues, or failure to tolerate conditioning. Because they never appear in entries or field-size statistics, they are largely invisible in population discussions.
Viewed as a funnel, the population problem becomes clear. From an already diminished foal crop, 29% of horses never race. Of those that do, a segment disappears from ages 2-3. The racing population therefore contracts far more rapidly than breeding numbers alone would suggest. This helps explain why efforts focused solely on increasing the foal crop or adjusting race conditions have failed to reverse declining field sizes.
Even when breeding stabilizes, the industry continues to lose horses at an unsustainable rate before and immediately after they enter competition. What, then, is driving this early and persistent attrition? Veterinary literature, regulatory reviews, and necropsy findings consistently identify a combination of physical factors that shorten Thoroughbred careers well before catastrophic injury occurs.
Musculoskeletal injury remains the most visible contributor. Stress fractures, condylar fractures, proximal sesamoid disease, and tendon and ligament injuries frequently develop during training and early racing. Multiple studies have demonstrated that catastrophic breakdown is often preceded by cumulative microdamage rather than acute trauma (Parkin et al., Equine Veterinary Journal, 2004; Martig et al., Veterinary Journal, 2014).
Necropsy findings from university diagnostic laboratories, including programs associated with University of California-Davis, have documented evidence of chronic bone remodeling abnormalities and premature skeletal aging in young racehorses. Respiratory disease is an equally important, though less visible, factor. Peer-reviewed studies report that 60%-80% of racehorses in active training show evidence of lower airway inflammation (Couëtil et al., Equine Veterinary Journal, 2007; Allen et al., Veterinary Record, 2011).
Conditions such as inflammatory airway disease and exercise-induced pulmonary hemorrhage impair oxygen exchange during both exertion and recovery. Chronic hypoxia has been associated with delayed tissue repair, impaired bone remodeling, and increased susceptibility to musculoskeletal injury (McKenzie, Rational Therapy of Inflammatory Airway Disease, 2011). These conditions rarely occur in isolation. Veterinary research increasingly emphasizes cumulative systemic inflammation, in which airway disease, repetitive microtrauma, and metabolic stress interact to compromise collagen integrity, tendon resilience, and skeletal repair (Fraipont et al., Veterinary Record, 2011).
Training interruption itself further accelerates attrition. Horses removed from training early are significantly less likely to return to sustained competition, even when the original injury resolves (Perkins et al., Equine Veterinary Journal, 2005). Each interruption increases the likelihood of secondary injury, loss of conditioning, or owner decisions to retire the horse for economic or welfare reasons. Even among horses that remain active, career length has shortened. Average starts per horse and total seasons raced have declined over time, reducing the effective population available to fill races even when starter counts appear stable.
A system built on diagnosis, not prevention
Despite these well-documented patterns, the medical framework of modern racing remains largely reactive rather than preventive. The industry has invested heavily in advanced diagnostic imaging, post-injury testing, and pre-race screening—tools designed to identify pathology once damage already has occurred.
While diagnostic oversight is essential for safety, it does little to address the upstream biological processes that lead to injury and early attrition. Bone microdamage, airway inflammation, and systemic hypoxia develop gradually, often long before they are visible on imaging or severe enough to fail a regulatory exam. By the time these issues are detected, the horse's capacity to adapt and remain in training may already be compromised. In this sense, the industry's medical focus mirrors its population strategy: It measures failure well, but prevention poorly.
There is limited structural emphasis on understanding how environment, respiratory health, recovery physiology, and cumulative inflammation interact to determine whether a horse can withstand training over time. As a result, horses continue to exit the system early—sometimes without a dramatic injury, but with a steady erosion of durability. If the industry continues to rely primarily on post-injury diagnostics rather than preventive health strategies, the outcome is predictable. Diagnostic tools may reduce catastrophic events, but they will not rebuild the racing population.
In fact, as scrutiny increases without corresponding improvements in prevention, the number of horses removed from competition is likely to rise, not fall. Taken together, the data point to a central conclusion: The racing population problem is driven less by participation or opportunity and more by physical durability. Horses are leaving the system not because they are unwanted or unentered, but because they cannot remain biologically resilient through training and early racing.
The industry has framed the population debate around economics, regulation, and breeding volume. Those factors matter. But without addressing the underlying causes of early physical attrition--and without shifting from a reactive medical model to one that emphasizes prevention, adaptation, and durability--efforts to rebuild the racing population will continue to fall short. The population crisis is not only about how many horses are born. It is about how many are able to stay healthy, adaptable, and sound long enough to race.
Christine Sanchez is a Thoroughbred owner and a specialist at Equicibus, a Florida-based provider of flax-based animal bedding and sustainable manure management services.
