HBLB Research on Injuries in Flat Racing: Nature versus Nurture

HBLB Research on Injuries in Flat Racing: Nature versus Nurture

  HBLB Research on Injuries in Flat Racing: Nature versus Nurture    Note: This research for this article, reprinted from European Trainer, was performed over a 14-year period in Great Britain and therefore only takes into account racing over turf and all-weather surfaces, but we feel that despite not including dirt statistics, the information is thought-provoking and of interest to our North American readers, especially with the increase in turf racing particularly in the U.S.       Musculoskeletal injuries are an inherent risk of horseracing, and they are the primary cause of Thoroughbreds failing to train and race, or even retiring altogether. In addition to the evident equine welfare concerns, racehorse injuries also have economic consequences and impact on jockey safety. The industry remains committed to investigating causes of injury and associated risk factors, which can inform strategies aimed at minimizing their occurrence. Advancements in methods of identification, management, and prevention of musculoskeletal disease and injury in Thoroughbreds and improved training and racing environments to enhance the safety, health, and wellbeing of racehorses have long been strategic priorities of the Horserace Betting Levy Board (HBLB)’s veterinary research funding program in Great Britain.     In 2014, the HBLB funded a research team at the Royal Veterinary College in London to undertake a detailed study of injuries and other veterinary events occurring in flat racehorses on race day. The purpose of the project was to establish causes of fatal and non-fatal injuries occurring in British flat racing and to examine associated risk factors. The research also set out to measure heritability of common injury types and conditions, and to investigate genetic and environmental correlations between injury and race performance.    The study team had access to detailed race and performance data from all Thoroughbreds racing on the flat in Great Britain over a 14-year study period from 2000 – 2013. These were then linked to veterinary reports of injury or conditions attended to by a veterinary surgeon on race day over the same time period, provided by the British Horseracing Authority (BHA). Finally, extensive pedigree data were added to enable investigation of heritability of race day injury and genetic correlations between injury types, and between injury and performance.     Descriptive findings    The final 14-year dataset included nearly 68,000 horses making over 800,000 starts in around 77,000 flat races. The majority of races -- 67% of them -- were run on the turf, with 33% of races taking place on all-weather tracks.    Just under 8,000 veterinary events were recorded over the study period, from which an incidence of nine events per 1000 starts was calculated. The most common incidents requiring veterinary attention on the racecourse were soft tissue injuries other than tendon and ligament injuries, e.g. wounds, lacerations, or muscle strains. Unspecified lameness and respiratory conditions were also common, accounting for around a fifth of veterinary reports each. Less than 10% of veterinary events had a fatal outcome, and the overall incidence of fatality was 0.8 per 1000 starts. Although bone injury was cited in only 14% of the veterinary reports overall, they accounted for the vast majority (77%) of the fatalities.    All-weather racing    Racing on all-weather tracks traditionally carries a higher risk of injury than racing on turf, which was reaffirmed in the current analyses. Therefore, the researchers also specifically investigated risk factors for fatality, distal limb fracture, and epistaxis (nose bleeds) in all-weather racing. These analyses were restricted to the ca. 258,000 all-weather starts in the dataset and included additionally collected information from the racecourse clerks on surface types and maintenance. The fatality incidence in all-weather racing was 0.9 per 1000 starts. Distal limb fracture occurred in around 1 in 1000 starts and epistaxis in 1.6 per 1000 starts. Risk factors varied for each outcome, although some factors were similar across outcomes including the going, racing intensity, horse age, age at first start, and horse and trainer performance variables. Generally, older horses and those that had started racing at an older age were at higher risk of an adverse outcome although for fatality, older horses that had started racing as two-year-olds were at highest risk. This association may be due to accumulation of microdamage in bone, which increases with increasing age as an effect of exercise accumulation over time and can ultimately lead to failure.  The finding that horses that start racing at an older age may be at increased risk of injury is not novel, and it has been suggested that those which do not race at two may be prevented from doing so due to underlying clinical problems. Injuries, or other clinical conditions, at an early age are also likely to interfere with training programs, which may result in a lack of musculoskeletal adaptation during a time when the skeleton is most responsive to exercise. Increasing firmness of going and first race start were risk factors for both distal limb fracture and epistaxis, a finding that is consistent with previous studies. Also consistent with previous research was that longer race distances increased the likelihood of fatality but reduced the risk of epistaxis. This is likely to be due to the speed of the race, with faster races inducing greater pulmonary vascular pressure and higher peak loading forces. Epistaxis was also more likely to occur on fibersand surfaces and on second generation Polytrack, as compared to first generation Polytrack.     Risk factors for fatality    In addition to the specific investigations for all-weather racing, the research also considered data from all starts available. This confirmed that the risk of fatality was around 1.5 times higher on all-weather surfaces than turf. Increased firmness of the going, increasing racing distance, increasing average horse performance, first year of racing, and wearing eye cover for the first time all increased the risk of fatality. The latter finding has not been reported previously, and it is currently unclear why wearing eye cover for the first time should increase the risk of fatality. Perhaps this could be due to a change in the horse’s depth perception or ability to judge distance, detect changes in the racing surface, or avoid interference by other horses.  Alternatively, it could be that trainers decide to use eye cover in an attempt to enhance performance, with poor performance resulting from subclinical pathology. Such horses would be at higher risk of (fatal) injury, in particular when wearing eye cover for the first time. Further research in this area, particularly investigating when and why eye cover is used in flat racing horses and how eye cover affects the vision and the performance of horses under race conditions, is warranted.     Another novel finding was that horses racing in an auction race were at 1.5 times higher risk of fatality compared with horses not racing in this race type. Auction races are for two- or three-year-olds that were sold at specific public auction sales, and so this finding may reflect aspects of the quality of horses racing in this race type, which is difficult to measure.     It is noteworthy that there was significant variation in horse fatality risk amongst trainers, even after accounting for other risk factors in the analysis. While most trainers with a race day fatality only had one fatality over the study period, other trainers had more. Training practices are likely to play a role and may partly explain this finding, and further research incorporating training and exercise regimens into studies of this nature is sorely needed. Unfortunately, it was not possible to collect and incorporate training data into this large-scale retrospective study, and any such studies would likely have to be prospective and smaller scale, given that the keeping of training records is not compulsory and highly variable between training yards.     Risk factors for distal limb fracture    Separate analyses were also conducted to investigate risk factors for distal limb fracture, the overall incidence of which was 0.8 per 1000 starts. As for fatality, increasing firmness of the going, increasing racing distance, and horses in their first year of racing were at a higher risk of distal limb fracture, 50% of which had a fatal outcome.        Horses from trainers with high average performance but also a high proportion of runners failing to finish were more likely to sustain a fracture than horses from trainers with lower average performance.  As for fatality, training regimens may also play a role in explaining this finding, and it could be that trainers who employ more intense training strategies are more likely to be successful, but also have more injuries to their horses.     Other risk factors for distal limb fracture included sex, with uncastrated male horses being at highest risk, and older age. Race type was also associated with distal limb fracture, with horses in claiming and seller races being at higher risk. The reasons for this are unclear but may be related to the type and quality of horses in such races, or their being entered into these races due to previous poor performance, which may be related to underlying subclinical injury.     Heritability of injuries and other race-day veterinary events    Heritability is defined as the proportion of variation between individuals in a population that is due to genetic variation. This number can range from 0 (no genetic contribution) to 1 (all differences in a characteristic or trait reflect genetic variation). In this study, the heritability of 10 outcomes was calculated: fracture, tendon and ligament injury, joint injury, fatality, cardiac conditions, epistaxis, metabolic conditions, and ‘gait observations’ (unspecified lameness). Heritability estimates were adjusted for all environmental (i.e. non-genetic) risk factors identified from the previous analyses. Results showed that heritability estimates of race day veterinary events ranged from 0.06 for gait observations to 0.19 for tendon/ligament injury. These estimates are considered low to moderate, but they suggest that 19% of variation between individuals in tendon/ligament injury outcome is due to genetic variation.  Genetic contributions to tendon injury have been identified in previous studies, in both horses and man.     Correlations between injuries and between injury and performance    The purpose of this analysis was to establish whether different types of injury were correlated within sires, trainers, or jockeys. In other words, are sires whose offspring is susceptible to e.g. fracture also more likely to have tendon-injury susceptible offspring, or do trainers with more fractures in their horses also have more (non-fracture) joint injury events recorded? Similarly, we also wanted to find out whether there were correlations between performance measures and veterinary events. Results showed that there was a high correlation between fatality and fracture at all levels (sire, trainer, and jockey level, although less so in the latter). This is somewhat unsurprising, given that fracture was the main cause of fatality. All other veterinary-event-to-veterinary-event correlations were low. Career length, career earnings, and race value were considered as measures of racehorse performance. No significant correlations were identified between these performance measures and veterinary events.     Implications of the findings    This large-scale study has provided up-to-date information on veterinary events and causes of fatality occurring in flat racing Thoroughbreds in Great Britain. Results can serve as a baseline for monitoring trends over time and evaluate the effect of potential interventions.     Risk factor analyses confirmed a number of factors that had previously been identified as increasing injury or fatality risk, such as racing on all-weather surfaces, increasing race distance, and firmness of the going. However, novel risk factors were identified for each outcome evaluated, including wearing eye cover for the first time, which increased the risk of fatality; racing in seller or claiming, which increased the risk of distal limb fracture; racing on second-generation Polytrack, which increased the risk of epistaxis in all-weather racing; and measures of trainer performance, which were associated with distal limb fracture. There was also significant trainer variation in race day fatality risk, after accounting for the other fatality risk factors. Although more research would be required to establish the reasons for some of these findings, exploring potential interventions targeted at “higher risk” groups may be warranted. Further work is ongoing to establish whether we can better predict adverse outcomes at the individual level, which could lead to more specific interventions in horses identified to be at particular risk in a specific race.          This study has also, for the first time, established the heritability of various outcomes after adjusting for known environmental risk factors. It is also the first time that correlations between different injury types, and between injury and performance, have been quantified. Given that there were no strong correlations between non-fatal injury events, interventions aimed at reducing one type of injury should not adversely affect occurrence of other injury types. Equally, interventions aimed at reducing injury occurrence should not adversely affect performance, given that the correlation between injury and performance was also low.      Acknowledgements    The authors are grateful to the HBLB for funding this important work and for their ongoing commitment to support veterinary research aimed at improving our understanding of issues affecting racehorse health and welfare. We are also indebted to our collaborators at the British Horseracing Authority and Weatherbys for provision of injury, performance, and pedigree data. Our co-worker Ruby Chang is acknowledged for her invaluable contributions to the ‘Nature versus Nurture’ project.

By Kristien Verheyen & Sarah Rosanowski

Musculoskeletal injuries are an inherent risk of horseracing, and they are the primary cause of thoroughbreds failing to train and race, or even retiring altogether. In addition to the evident equine welfare concerns, racehorse injuries also have economic consequences and impact on jockey safety. The industry remains committed to investigating causes of injury and associated risk factors, which can inform strategies aimed at minimising their occurrence. Advancements in methods of identification, management, and prevention of musculoskeletal disease and injury in Thoroughbreds and improved training and racing environments to enhance the safety, health, and wellbeing of racehorses have long been strategic priorities of the Horserace Betting Levy Board (HBLB)’s veterinary research funding program in Great Britain.

In 2014, the HBLB funded a research team at the Royal Veterinary College in London to undertake a detailed study of injuries and other veterinary events occurring in flat racehorses on race day. The purpose of the project was to establish causes of fatal and non-fatal injuries occurring in British flat racing and to examine associated risk factors. The research also set out to measure heritability of common injury types and conditions, and to investigate genetic and environmental correlations between injury and race performance.

The study team had access to detailed race and performance data from all Thoroughbreds racing on the flat in Great Britain over a 14-year study period from 2000 – 2013. These were then linked to veterinary reports of injury or conditions attended to by a veterinary surgeon on race day over the same time period, provided by the British Horseracing Authority (BHA). Finally, extensive pedigree data were added to enable investigation of heritability of race day injury and genetic correlations between injury types, and between injury and performance.

Descriptive findings

The final 14-year dataset included nearly 68,000 horses making over 800,000 starts in around 77,000 flat races. The majority of races -- 67% of them -- were run on the turf, with 33% of races taking place on all-weather tracks.

Leading image (2).jpg

Just under 8,000 veterinary events were recorded over the study period, from which an incidence of nine events per 1000 starts was calculated. The most common incidents requiring veterinary attention on the racecourse were soft tissue injuries other than tendon and ligament injuries, e.g. wounds, lacerations, or muscle strains. Unspecified lameness and respiratory conditions were also common, accounting for around a fifth of veterinary reports each. Less than 10% of veterinary events had a fatal outcome, and the overall incidence of fatality was 0.8 per 1000 starts. Although bone injury was cited in only 14% of the veterinary reports overall, they accounted for the vast majority (77%) of the fatalities.

All-weather racing

Racing on all-weather tracks traditionally carries a higher risk of injury than racing on turf, which was reaffirmed in the current analyses. Therefore, the researchers also specifically investigated risk factors for fatality, distal limb fracture, and epistaxis (nose bleeds) in all-weather racing. These analyses were restricted to the ca. 258,000 all-weather starts in the dataset and included additionally collected information from the racecourse clerks on surface types and maintenance. The fatality incidence in all-weather racing was 0.9 per 1000 starts. Distal limb fracture occurred in around 1 in 1000 starts and epistaxis in 1.6 per 1000 starts. Risk factors varied for each outcome, although some factors were similar across outcomes including the going, racing intensity, horse age, age at first start, and horse and trainer performance variables. Generally, older horses and those that had started racing at an older age were at higher risk of an adverse outcome although for fatality, older horses that had started racing as two-year-olds were at highest risk. This association may be due to accumulation of microdamage in bone, which increases with increasing age as an effect of exercise accumulation over time and can ultimately lead to failure.  

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