The Effect of Combined Training and Racing High-Speed Exercise History on Musculoskeletal Injuries in Thoroughbred Racehorses: A Systematic Review and Meta-Analysis of the Current Literature

Abstract

Despite over three decades of active research, musculoskeletal injuries (MSI) remain a global problem for the Thoroughbred (TB) racing industry. High-speed exercise history (HSEH) has been identified as an important risk factor for MSI. However, the nature of this relationship remains unclear, with an apparent protective effect of HSE against injury, before it becomes potentially harmful. Many MSI cases and fatalities occur during training rather than during racing, resulting in an underestimation of injury from studies focused on race day. The objective of this study was to examine the current evidence of the effect of combined training and racing HSEH on MSI in TB flat racehorses, through a systematic review and meta-analysis. A systematic search of the relevant literature was performed using PubMed®, Scopus®, Web of Science®, and Embase® online databases and the gray literature using sites containing “.edu” or “.edu.au”. Studies included in the review had explored seven different measures of HSE, including total career HSE distance, cumulative HSE distance in the 30 and 60 days before MSI, average HSE distance per day, per event and per 30 days, and the total number of HSE events. The total cumulative career HSE distance significantly affected the odds of MSI, with every 5-furlong increase, the odds of MSI increased by 2% (OR = 1.02; 95% CI 1.01, 1.03; p = 0.004). The average HSE distance per day also affected the odds of MSI, with every additional furlong increasing the odds of MSI by 73% (OR = 1.73; 95% CI 1.29, 2.31; p < 0.001). Other measures of HSE were not found to be consistently associated with risk of MSI, but these results should be interpreted with caution. Significant methodological limitations were identified and influence the comparability of studies. Standardizing the measures of HSE in studies of MSI, and describing training conditions in more detail, would support a more thorough investigation of the relationship between HSE and MSI. An improved understanding of this relationship is critical to mitigating the impact of MSI in the Thoroughbred racehorse.

Date of birth and purchase price as foals or yearlings are associated with Thoroughbred flat race performance in the United Kingdom and Ireland

“…This seems counterintuitive because expensive horses might need to race more often to recover the investment; as suggested in a previous study, which observed a positive association between purchase price as yearling and the number of race starts 11 . Our findings might therefore suggest that in the UK, expensive horses are purchased with a view to entering them in selected prestigious, higher value races, a strategy that may also reduce the risk of injury due to race overload 24 …”

“…11 Our findings might therefore suggest that in the UK, expensive horses are purchased with a view to entering them in selected prestigious, higher value races, a strategy that may also reduce the risk of injury due to race overload. 24 Despite the lower number of races run by expensive compared with less expensive horses, purchase price as foals and yearlings was positively associated with race performance by the end of the third year of life. The most expensive foals and yearlings earned more prize money and prize money per start as 3-year olds than the less expensive ones.…”

Factors Associated with Mortality in Ontario Standardbred Racing: 2003–2015

“…Our performance indices emphasized cumulative work and examined their relationship to general mortality odds. Effects depended on unit of interest, while the relationship between work, age and career stage is complex in the horse [ 18 , 60 , 61 ]. At the work-event level, increasing annual work duration and frequency were associated with decreasing mortality odds for young horses, indicating horses were at greatest risk when first entering training [ 62 ], and possibly response to training for successful horses.…”

Factors Associated with Fatality in Ontario Thoroughbred Racehorses: 2003–2015

“…Associations are then examined between horse, work, and racing environment factors and these adverse outcomes to gain insights into causation and identify preventive strategies. This approach has been particularly useful for MSI, the greatest source of loss [7,[9][10][11][12][13], and many risk factors have been identified. Among other discoveries, it has led to recognition of the importance of bone strength and density and the manner in which this accrues, the importance of micro fractures, accumulated strain and the time required for adequate healing or adaptation to take place, and the overall impact of cumulative wear and tear [13][14][15][16][17].…”