Horse-level risk factors for fatal distal limb fracture in racing Thoroughbreds in the UK

Department of Veterinary Clinical Science, University of Liverpool Veterinary Teaching Hospital, Leahurst, Neston, Wirral CH64 7TE, UK.
Equine Veterinary Journal (Impact Factor: 2.37). 10/2004; 36(6):513-9. DOI: 10.2746/0425164044877332
Source: PubMed


Fractures below the level of the radius or tibia (distal limb fractures) are the most common cause of equine fatality on UK racecourses; however, little is known about their epidemiology or aetiology. Identification of risk factors could enable intervention strategies to be designed to reduce the number of fatalities.
To identify horse-level risk factors for fatal distal limb fracture in Thoroughbreds on UK racecourses.
A case-control study design was used. Fractures in case horses were confirmed by post mortem examination and 3 matched uninjured controls were selected from the race in which the case horse was running. One hundred and nine cases were included and information was collected about previous racing history, horse characteristics and training schedules. Conditional logistic regression was used to identify the relationship between a number of independent variables and the likelihood of fracture.
Horses doing no gallop work during training and those in their first year of racing were at significantly increased risk of fracture on the racecourse. Case horses were also more likely to have trained on a sand gallop, i.e. a gallop described by trainers as being primarily composed of sand.
Modifications to training schedules, specifically within the first year of racing, may have a large impact on the risk of fatal distal limb fracture on the racecourse. Horses should do some gallop work in training and our results suggest that the minimum distance galloped should be between 805-2012 m (4-10 furlongs)/week.
The information from this study can be used to alter training schedules in an attempt to reduce the incidence of fatal distal limb fracture in Thoroughbred racehorses. Training should include some gallop work, and further studies, recording the exact level of work, will help to identify an optimum range of training speeds and distances which will reduce the liklihood of catastrophic fracture on the racecourse.

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    • "In addition to genetic differences between the populations there are also differences in the environmental risks experienced. The risk of fracture depends on the type of racing: flat turf racing is the safest (0.4 fatal fractures/1000 starts) whilst National Hunt racing is associated with the highest risk (2.2 fatal fractures/1000 starts) [11]. The increase in environmental risk for National Hunt racehorses could make the ascertainment of genetically susceptible horses from this population more difficult, potentially decreasing the power of a genetic study. "
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    ABSTRACT: Thoroughbred racehorses are subject to non-traumatic distal limb bone fractures that occur during racing and exercise. Susceptibility to fracture may be due to underlying disturbances in bone metabolism which have a genetic cause. Fracture risk has been shown to be heritable in several species but this study is the first genetic analysis of fracture risk in the horse. Fracture cases (n = 269) were horses that sustained catastrophic distal limb fractures while racing on UK racecourses, necessitating euthanasia. Control horses (n = 253) were over 4 years of age, were racing during the same time period as the cases, and had no history of fracture at the time the study was carried out. The horses sampled were bred for both flat and National Hunt (NH) jump racing. 43,417 SNPs were employed to perform a genome-wide association analysis and to estimate the proportion of genetic variance attributable to the SNPs on each chromosome using restricted maximum likelihood (REML). Significant genetic variation associated with fracture risk was found on chromosomes 9, 18, 22 and 31. Three SNPs on chromosome 18 (62.05 Mb - 62.15 Mb) and one SNP on chromosome 1 (14.17 Mb) reached genome-wide significance (p < 0.05) in a genome-wide association study (GWAS). Two of the SNPs on ECA 18 were located in a haplotype block containing the gene zinc finger protein 804A (ZNF804A). One haplotype within this block has a protective effect (controls at 1.95 times less risk of fracture than cases, p = 1 x 10-4), while a second haplotype increases fracture risk (cases at 3.39 times higher risk of fracture than controls, p = 0.042). Fracture risk in the Thoroughbred horse is a complex condition with an underlying genetic basis. Multiple genomic regions contribute to susceptibility to fracture risk. This suggests there is the potential to develop SNP-based estimators for genetic risk of fracture in the Thoroughbred racehorse, using methods pioneered in livestock genetics such as genomic selection. This information would be useful to racehorse breeders and owners, enabling them to reduce the risk of injury in their horses.
    Full-text · Article · Feb 2014 · BMC Genomics
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    • "In TBR, age and gender have been shown to be specific risk factors for injury development, with older animals being at increased risk of tendon and ligament traumas [13-17] and females being more at risk of stress fractures [3,5]. Racetrack surface [2,3], age [1,3,6], gender [1,6,16,17], season [3,5,16], trainer [4,5,15-17], pre-existing pathologies [18-20], accumulation of exercise at racing speed [21,22], average distance run per week [23,24], laying-up periods [2,22] and inter-race interval [2,22] have all been studied in TBR populations, with contradictory results. Also, shoeing techniques received great attention [19,25,26]; particularly one of them, the toe grab, is a recognized risk factor for MSI in TBR due to the alteration of the horse’s gait at high speed [19,26]. "
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    ABSTRACT: There is a substantial paucity of studies concerning musculoskeletal injuries in harness Standardbred racehorses. Specifically, little is known about the epidemiology of exercise-related musculoskeletal injuries. Most studies on this subject involve Thoroughbred racehorses, whose biomechanics and racing speed differ from Standardbred, making comparisons difficult. Here, a population of Standardbred racehorses trained at the same racecourse was studied over four years and a classification system for exercise-related musculoskeletal injuries was designed. The incidence rates of musculoskeletal injuries causing horses' withdrawal from training for 15 days or longer were investigated. A mixed-effects Poisson regression model was used to estimate musculoskeletal injury rates and to describe significance of selected risk factors for exercise-related injuries in this population. A total of 356 trotter racehorses from 10 different stables contributed 8961 months at risk of musculoskeletal injuries. Four-hundred-and-twenty-nine injuries were reported and classified into 16 categories, based on their aetiology and anatomical localisation. The overall exercise-related injury rate was 4.79 per 100 horse months. When considering risk factors one by one in separate univariable analyses, we obtained the following results: rates did not differ significantly between genders and classes of age, whereas one driver seemed to cause fewer injuries than the others. Racing speed and racing intensity, as well as recent medical history, seemed to be significant risk factors (p < 0.001), while being shod or unshod during racing was not. On the other hand, when pooling several risk factors in a multivariable approach, only racing intensity turned out to be significant (p < 0.001), since racing speed and the racing intensity were partially confounded, being strongly correlated to one another. Characterizing epidemiology of exercise-related musculoskeletal injuries in trotter racehorses provides baseline incidence rate values. Incidence rates of stress fracture are lower in Standardbreds compared to Thoroughbreds, whereas the opposite is true for tendon and suspensory ligament injuries. In addition to identification of risk factors for musculoskeletal injuries among Standardbred racehorses, results suggest that racing intensity seems to be a protective predictor of risk and recent medical history could be used to identify horses at risk of injury.
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    • "The frequency and severity of MSC create a substantial financial burden for the racing industry, compromise equine welfare and create negative publicity for the sport. Many previous studies have attempted to identify risk factors for MSC in racehorses (see, for example, Stephen et al., 2003; Ely et al., 2004; Parkin et al., 2004a; Pinchbeck et al., 2004; Jacklin and Wright, 2012). These studies varied in many ways, including case definition, identity of the target population, and whether diagnoses were made in racing and/or training. "
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    ABSTRACT: A retrospective cohort study of important musculoskeletal conditions of Thoroughbred racehorses was conducted using health records generated over a 15 year period (n = 5062, 1296 sires). The prevalence of each condition in the study population was: fracture, 13%; osteoarthritis, 10%; suspensory ligament injury, 10%; and tendon injury, 19%. Linear and logistic sire and animal regression models were built to describe the binary occurrence of these musculoskeletal conditions, and to evaluate the significance of possible environmental risk factors. The heritability of each condition was estimated using residual maximum likelihood (REML). Bivariate mixed models were used to generate estimates of genetic correlations between each pair of conditions. Heritability estimates of fracture, osteoarthritis, suspensory ligament and tendon injury were small to moderate (range: 0.01–0.20). Fracture was found to be positively genetically correlated with both osteoarthritis and suspensory ligament injury. These results suggest that there is a significant genetic component involved in the risk of the studied conditions. Due to positive genetic correlations, a reduction in prevalence of one of the correlated conditions may effect a reduction in risk of the other condition.
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