Abstract
Simple SummaryOf common debate among equine professionals and enthusiasts alike, is whether entering race training at two years of age is detrimental or beneficial to the animal’s career and growth. This literature review evaluates epidemiological studies to elucidate that two-year-old horses are not at greater risk of injury compared to older horses. Horses which enter race training at two years of age are, in fact, found to have greater earnings and longer race careers. This review also tackles the impact that exercising an animal at two years of age or younger has on bone, articular cartilage, and tendons. Numerous studies on growing animals have found confinement to be detrimental to normal musculoskeletal growth. However, exercise of dynamic nature in moderate distances, such as that attained with pasture access or prescribed sprints, is beneficial to musculoskeletal development and may prevent injuries when entering race training. Based on scientific evidence, the research cited in this review supports the training and racing of two-year-old horses and advises caution in the use of medications such as corticosteroids.Conflicting research and anecdotal evidence have created disagreement among equestrians as to whether two-year-old horses should be trained and raced. The objective of this literature review is to evaluate epidemiological studies, as well as physiological data on equine bone, articular cartilage, and tendons to better determine the impact of training and racing two-year-old horses. The evaluation of numerous studies on the topic provides evidence that a horse which is trained or raced as a two-year-old has a lower risk of injury and better adapted tissues for the rigors of racing. Unfortunately, the current prolific use of pain-mitigating substances in the racing industry does place horses, including young cohorts, at greater risk of injury, and should be used with caution.
Highlights
In 2018, the Thoroughbred racehorse Justify won the Grade I Kentucky Derby, and subsequently went on to capture the North American Triple Crown by winning the Preakness Stakes (Grade 1 Stakes race—GI) and Belmont Stakes (GI)
In horses that were 19 months of age, high intensity exercise on treadmills increased the cross-sectional area of the common digital extensor tendon but not of the SDFT, suggesting that the SDFT was no longer adaptable to exercise in horses of this age [55]
Training does have a hypertrophic effect on some tendons, but the SDFT and SL of horses as young as 2 years of age do not appear to increase in cross sectional area in response to training
Summary
In 2018, the Thoroughbred racehorse Justify won the Grade I Kentucky Derby, and subsequently went on to capture the North American Triple Crown by winning the Preakness Stakes (Grade 1 Stakes race—GI) and Belmont Stakes (GI). Having never having raced as a two-year-old, social media was filled with opinions that the onset of training should be delayed until horses are more mature. Justify’s win was attempted to be used as evidence of the benefit of not racing until a horse is three years old or older. Justify was the first horse since Apollo, who won the Kentucky Derby in 1882, to have won the race without racing as a two-year-old. In the 136 years between Apollo and Justify winning the Kentucky Derby, over 60 horses who were unraced as two-year-old’s have attempted this feat without success [1]. The question that remains, is whether waiting until the horse is more skeletally mature is beneficial to the soundness and longevity of a racehorse or other equine athletes. Rather than rely on anecdotal evidence, opinions, or traditional beliefs, the best way to answer this is to evaluate the scientific literature for evidence based upon epidemiological studies and an understanding of how the skeleton and other related tissues respond to training and mechanical stress
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