Anomalous Incidence of Fatal Musculoskeletal Injury in North American 2-Year-Old Thoroughbred Racehorses in the Year 2020

SIMPLE SUMMARY: In the early stages of the global COVID-19 pandemic, many countries implemented strong anti-infection mitigations. In the United States and Canada, these measures affected the training regimens of Thoroughbred racehorses—pandemic mitigations meant that ‘normal’ training schedules could not be followed. These circumstances led to a natural experiment: many 2-year-old Thoroughbreds, who would normally have begun intensive preparation for starting their racing careers in early 2020, had the beginning of their training delayed. Meanwhile, horses aged 3 years and older also experienced an interruption to their normal or expected training programmes. On full analysis of the 2020 annual statistics on behalf of The Jockey Club, an increase in the number of fatal musculoskeletal injuries among 2-year-old horses compared to previous years was observed. No similar increase was seen among horses aged 3 years and older in 2020. In 2020, 2-year-olds were the age group with the highest risk of fatal injury. In 2021 and 2022, the incidence of fatalities in 2-year-old horses returned to the previous trend. In all previous (to 2020) and the two subsequent years, the risk of fatal musculoskeletal injury has been lowest in 2-year-old horses, compared with 3- and 4+-year-olds. This result emphasises the importance of racehorses following a suitable training schedule, especially for racehorses at the beginning of their career. ABSTRACT: Racehorse training and racing schedules in many parts of the United States and Canada were interrupted or otherwise reduced during the first three to six months of 2020. This was an indirect consequence of mitigations to prevent the spread of the pandemic virus COVID-19. Data from the Equine Injury Database, a census-level survey of all race starts made in the USA and Canada, were used to analyse the incidence of fatalities in 2009–2022 among three age cohorts of racehorses within each year. There was a statistically significant increase in the incidence of musculoskeletal fatalities among 2-year-old Thoroughbreds in 2020, compared to the period 2009–2019. In 2021 and 2022, the training schedules of 2-year-old horses returned to pre-2020 levels, as did the incidence of fatalities. The delayed start to training for 2-year-old horses was associated with an increase in risk of fatal musculoskeletal injury for those horses during 2020, but the risk for the same horses in 2021—when they were 3 years old—was not significantly different to the risk for 3-year-olds in any other year. The increased risk of fatal musculoskeletal injury in 2020 was only found among horses that were 2 years old in 2020—horses aged 3 years or more in 2020 were not at increased risk.