The debate surrounding the optimal age for initiating race training in young horses is a long-standing one among equine professionals and enthusiasts. While some advocate for delaying training until horses reach skeletal maturity to prevent injuries, emerging scientific evidence suggests that early training and racing can actually be beneficial for a horse’s career longevity and overall musculoskeletal health. This review synthesizes epidemiological studies and physiological data on equine bone, articular cartilage, and tendons to provide a comprehensive understanding of the impact of training two-year-old horses.
The Case for Early Training: Epidemiological Evidence
Epidemiological studies consistently indicate that musculoskeletal injuries are the primary reason for racehorse turnover. However, contrary to popular belief, research suggests that two-year-old racehorses are not at a greater risk of injury compared to older horses. In fact, a meta-analysis found that horses with their first start at two years of age had a reduced risk of fatal lateral condylar fractures compared to those starting at three or four years of age. Furthermore, horses that enter race training at two years old tend to have more race starts, greater earnings, and longer racing careers. This early exposure to training, even if not full racing, provides positive stimuli that benefit musculoskeletal development. Studies have also shown that a higher age at first race start can increase the risk of retirement from racing, while a greater number of starts as a two-year-old is associated with a lower risk of retirement and a higher average distance raced.
The seemingly counterintuitive findings regarding injury risk may be explained by how young horses’ bones adapt to mechanical stress. Wolff’s Law posits that bone adapts to its environment, and dynamic exercise during growth can lead to beneficial changes in bone morphology, increased fracture force, and reduced fracture risk at maturity. Conversely, confinement and lack of exercise can be detrimental to musculoskeletal development. Interestingly, even young horses with open growth plates (epiphyseal plates) have shown a higher rate of soundness compared to those with closed plates, suggesting that activity before full skeletal maturity can be advantageous.
Impact on Key Musculoskeletal Tissues
Bone Health and Adaptation
Bone is a dynamic tissue that constantly undergoes modeling and remodeling to adapt to mechanical loads. Exercise, particularly dynamic loading, stimulates osteoblasts to form new bone, increasing bone strength and reducing fracture risk. Short-term dynamic exercise during adolescence can lead to lifelong benefits in bone quality and strength. Conversely, confinement and lack of sufficient strain can lead to bone loss. While conditions like “bucked shins” (dorsal metacarpal disease) are common in young horses, they are often attributed to management practices, such as confinement and lack of adequate sprint exercise, rather than age itself. Introducing short-distance, high-speed work earlier in training, rather than prolonged slow exercise, can help prevent bucked shins and prepare young horses for the demands of racing.
Articular Cartilage Resilience
Articular cartilage, the smooth lining of synovial joints, relies on regular movement and dynamic loads to maintain its structure and function. While strenuous long-term exercise can lead to site-dependent changes in cartilage composition, moderate exercise appears to be beneficial. Inactivity is detrimental to cartilage health, while exercise can lead to increased stiffness and potentially earlier maturation of cartilage components. Studies suggest that excessive sprinting can have deleterious effects, but moderate sprint exercise, when balanced with pasture access, can support joint development. The key lies in finding the right balance of exercise intensity and frequency to promote cartilage health without causing overload.
Tendon and Ligament Strength
Tendons and ligaments act as biological springs, storing and releasing energy to facilitate locomotion and reduce the energetic cost of movement. The superficial digital flexor tendon (SDFT) and suspensory ligament (SL) are particularly prone to injury due to the significant strains they endure. While mature tendons have limited adaptability, young horses’ tendons are more responsive to exercise. Training can increase the tensile strength, stiffness, and cross-sectional areas of tendons. Early exposure to exercise during growth, such as through pasture access or controlled sprinting, can lead to stronger tendons and a lower risk of injury later in life. Confinement without adequate exercise can negatively impact tendon maturation.
Critical Factors in Injury Prevention
While scientific evidence supports the benefits of early training, a significant portion of the equine community remains hesitant. This often stems from a belief that waiting until skeletal maturity is the safest approach. However, injury prevention is multifaceted and extends beyond just the age of training initiation. Flexibility in training schedules, allowing for adequate rest and recovery, and avoiding a “train by the calendar” mentality are crucial.
The use of pain-mitigating medications, such as corticosteroids, presents a significant concern. While these drugs can mask pain and allow horses to continue training through injuries, they interfere with the natural pain signals that warn animals of damage. This can lead to further tissue damage and catastrophic injuries. Studies have shown a correlation between corticosteroid use and an increased hazard for musculoskeletal injury. Implementing cut-off periods for intra-articular injections before races and workouts has been associated with a dramatic decrease in catastrophic injuries, suggesting that managing injuries through rest and healing, rather than masking pain, is paramount.
Conclusion
The available scientific evidence strongly suggests that training and racing two-year-old horses is not only safe but can be beneficial for their long-term musculoskeletal health and athletic careers. Early exposure to dynamic exercise promotes bone adaptation, supports cartilage function, and strengthens tendons and ligaments. However, responsible management, including appropriate training intensity, adequate rest, and cautious use of medications, is essential to maximize these benefits and minimize the risk of injury. Addressing the underlying causes of injury through proactive management and a deeper understanding of equine physiology will ultimately contribute to the well-being and longevity of equine athletes.
