Variation in conformation in a cohort of National Hunt racehorses

REASONS FOR PERFORMING THE STUDY: Assessment of conformation is commonly used in the selection of horses for performance purposes. Little information is available on the normal range of conformational traits within the Thoroughbred population. OBJECTIVES: To describe variations in conformation in a cohort of racing Thoroughbreds in order to provide a set of baseline standards within which conformational traits can be considered normal. MATERIALS AND METHODS: Ninety-eight conformational parameters were measured in a cohort of 108 National Hunt racehorses using a digital motion analysis system. The measurements consisted of segment lengths, joint angles in 2D and 3D, inclinations, deviations and circumference measurements. The differences between left and right sides were determined to obtain a measure of asymmetry. Conformational parameters were related to each horse's country of origin, preferred race distance and race type. RESULTS: The majority of parameters followed a normal distribution with the biggest relative variation in hoof related measurements and in stifle and coxal angle. All circumference measurements and the majority of the length measurements were significantly correlated with the height of the horse at the withers. No underlying pattern of combinations of conformational parameters was identified. Twenty-five per cent of the parameters showed a significant difference between left and right-sided measurements. A significant difference in girth and intermandibular width was observed between Irish and French horses. CONCLUSIONS: Thoroughbreds differ from other breeds, not only with regard to segment lengths but also with regard to joint angles and deviations. Variation in conformational parameters was relatively small and no distinct pattern of combinations of conformational traits identified. CLINICAL RELEVANCE: The variation in conformational measurements in Thoroughbred racehorses establishes a set of baseline measurements of conformational range against which individual horses can be assessed.     

The effect of conformation on orthopaedic health and performance in a cohort of National Hunt racehorses: preliminary results

REASONS FOR PERFORMING STUDY: There is a lack of scientific data and studies on the effect of conformation on performance or on orthopaedic health. OBJECTIVES: To investigate the relationship between conformation, injury and performance in racehorses used for racing over fences. METHODS: Over 2 years, 108 National Hunt racehorses were followed and their medical and performance data recorded. Conformation was measured in 3D with a computerised motion analysis system. Linear multiple regression models were used to evaluate the effect of conformation on measures of race performance and stepwise forward logistic regression models to assess the effect on risk of injury. RESULTS: An increase in intermandibular width, flexor angle of the shoulder joint and coxal angle (the angle between the ilium and ischium) was demonstrated to have a positive effect on performance. Performance decreased with increasing girth, length of the hind digit and valgus conformation of the metacarpophalangeal joint. The risk of suffering from superficial digital flexor tendon injury increased with increasing metacarpophalangeal joint angle and with carpus valgus conformation. The risk of pelvic fracture increased with valgus conformation of the tarsus and decreased with an increasing coxal angle. CONCLUSION: Valgus deformation was demonstrated to be detrimental to performance or increased risk of injury, perhaps resulting in higher loads on musculoskeletal structures. The coxal angle was the only parameter to have an effect on both risk of injury and performance. An alignment of the muscles with the axis of the pelvis may be beneficial for force transmission and decrease the bending moment of the muscles on the bones. The statistical power of this study is limited, however it provides preliminary data necessary for the planning of a larger scale study on the effect of conformation on performance and risk of injury. CLINICAL RELEVANCE: Studies of the effects of conformation on performance and risk of injury may aid in identifying individuals likely to perform well on the racecourse and avoid risks of injury.     

Descriptive results from a longitudinal study of airway inflammation in British National Hunt racehorses

Reasons for performing study: Rates of airway inflammation in young racehorses decrease with time but it is not clear whether this is associated with increasing age or time exposed to the training environment. The structure of the British National Hunt (NH) population allowed closer examination of this relationship. Objectives: To compare rates of inflammatory airway disease diagnosed by tracheal sampling (trIAD), and its components, in NH racehorses by age and training history and with published rates in young racehorses. Methods: A prospective, longitudinal study was conducted on 5 NH yards over 2 years. Period sample prevalences of nasal discharge, tracheal mucus, airway neutrophilia and trIAD (defined by a combination of tracheal mucus and airway neutrophilia) were estimated and compared between horses with different ages and time in training. Results: Horses new to training had twice the odds of visible tracheal mucus as ex‐flat trained horses (OR 2.0; 95% CI: 1.4–2.8; P<0.001) but no significantly increased odds of airway neutrophilia (OR 1.3; 95% CI: 0.8–1.9; P = 0.3) and inconclusive evidence of increased odds of trIAD (OR 1.8; CI: 0.9–3.5; P = 0.08). However, a lower median time in training was significantly associated with the presence of visible mucus (P<0.001), increased mucus (P = 0.005) and trIAD (P = 0.03). No disease measure varied significantly with age. Conclusions: Tracheal mucus and trIAD, but not neutrophilia detected in tracheal wash samples, were less prevalent in horses that had been exposed to the training environment for longer, explaining previously reported associations with age. Potential relevance: Neutrophil proportion in tracheal wash samples is not as useful a clinical tool as measures of visible tracheal mucus for identifying horses requiring treatment or changes in management. The inclusion of tracheal wash neutrophils in the assessment of equine airways, or at least their relative weighting in definitions of trIAD, should be re‐evaluated.     

The effect of training on stride parameters in a cohort of National Hunt racing Thoroughbreds: A preliminary study

Reasons for performing study: The influence of training on stride parameters is controversial and to date there is no information on how training influences stride parameters during high‐speed locomotion in the field. Objective: To determine the influence of training on stride variables during high‐speed locomotion in Thoroughbred racehorses. Methods: Speed, stride frequency, stance and protraction times were quantified in 8 Thoroughbreds with foot mounted accelerometers and GPS sensors during their first week of canter after the summer break and 6 months into training. Results: At a speed of 11 m/s, stride frequency was (mean ± s.d.) 2.160 ± 0.120 strides/s pre‐ and 2.167 ± 0.083 strides/s post training; mean stance time was 125.3 ± 9 ms pre‐ and 125.9 ± 7 ms post training; protraction time was 340.7 ± 20.4 ms pre‐ and 337.2 ± 14.3 ms post training. The increase in stride frequency and the decrease in protraction time after training were significant. There was no statistically significant difference in the maximum speed reached by each horse pre‐ and post training. Conclusions: Stance time stayed constant throughout the training season in the tested horses. A significant decrease in protraction time and a corresponding significant increase in stride frequency were observed after training. Potential relevance: Training of racehorses could be adapted to maximise the effect on modifiable parameters and reduce the risk of training‐induced pathologies. Further research will be conducted to investigate the effect of different training protocols on a large number of horses.     

Ultrasonographic assessment of the superficial digital flexor tendons of National Hunt racehorses in training over two racing seasons

Reasons for performing study: It is important to ascertain the prevalence of superficial digital flexor tendon (SDFT) injuries and to improve methods of predicting injury in National Hunt (NH) racehorses. Objectives: To establish: 1) the prevalence of SDFT tendinopathy in NH horses; 2) whether routine ultrasonography can be used to predict SDFT injuries; 3) whether previous tendinopathy predisposes to reinjury; 4) a normal range for the SDFT cross‐sectional area (CSA); and 5) the effects of gender, age, background (ex‐flat or exstore), limb, training and rest periods on SDFT CSA. Methods: Routine ultrasound assessment of the palmar metacarpal soft tissues of 263 NH racehorses was performed on up to 6 occasions over 2 NH racing seasons. Results: The prevalence of SDFT pathology detected using ultrasonography was 24% (n = 148), with a nonsignificant variation between yards of 10–40%. No changes in SDFT CSA or ultrasonographic appearance were detected prior to injury. Older horses had a significantly higher prevalence of SDFT pathology compared to younger horses, and horses with tendinopathy were more likely to suffer an acute injury compared to horses with no evidence of pathology. A reference range for normal CSA measurements was established as 77–139 mm² at level 4, from 142 horses with no ultrasonographic evidence of SDFT pathology. The CSA of normal horses did not vary significantly with age, limb or over 2 racing seasons, but did with sex and background. Conclusions: The study confirms that SDFT tendinopathy is common in NH horses, with substantial variation between training yards. Ultrasonography at 3 month intervals did not seem to predict acute SDFT injuries. Potential relevance: Variation in the prevalence of tendinopathy between yards suggests that training methods may influence injury rate. It was not possible to predict injury using routine ultrasonography and therefore other methods must be identified. A normal reference range for SDFT CSA is provided.     

Descriptive epidemiology of fracture,tendon and suspensory ligament injuries in National Hunt racehorses in training

Reasons for performing study: While fractures and tendon injuries are known to be important diseases in National Hunt (NH) racehorses during racing, there are no accurate estimates of their incidence in NH training yards. Objectives: To estimate the incidence of fractures and tendon and suspensory ligament injuries (TLIs) in NH racehorses in training; to describe the injuries incurred and to compare injury incidence rates by horse age, trainer, gender and background (ex‐flat vs. ex‐store horses). Methods: Cohort data were collected from 14 UK NH training yards for 2 racing seasons. Daily exercise regimens and details of fractures and TLIs occurring in study horses were recorded. Results: Data were gathered from 1223 horses that spent 9466 months at risk of injury. The fracture incidence rate was 1.1/100 horse months and varied significantly by trainer (P<0.001) but not by gender, age or background. The pelvis and third metacarpal bone (MCIII) were the most common fracture sites, although this varied between racing and training. The TLI incidence rate was 1.9/100 horse months and varied significantly by trainer (P = 0.05) and age (P<0.001) but not by gender or background. However, exstore horses were significantly more likely to have a TLI on the racecourse than ex‐flat horses (P = 0.01). Superficial digital flexor injuries accounted for 89% of all TLIs, the remainder being suspensory ligament injuries. Conclusions and potential relevance: Fractures and TLIs are important causes of morbidity and mortality in NH racehorses in training in England. This study provides accurate estimates of their incidence in this population and provides a baseline against which to monitor the effect of future interventions.     

A prospective cohort study to investigate risk factors for horse falls in UK hurdle and steeplechase racing

REASONS FOR PERFORMING STUDY: Equine fatalities during racing continue to be a major welfare concern and falls at fences are responsible for a proportion of all equine fatalities recorded on racecourses. OBJECTIVES: To identify and quantify risk factors for horse falls in National Hunt (NH) racing and to report the frequency of falling and falling-associated fatalities. METHODS: A prospective cohort study was conducted on 2879 horse starts in hurdle and steeplechase races on 6 UK racecourses. Any horse that suffered a fall at a steeplechase or hurdle fence during the race was defined as a case. Data were obtained by interview and observations in the parade ring and from commercial databases. Multivariable logistic regression models, allowing for clustering at the level of the track, were used to identify the relationship between variables and the risk of falling. RESULTS: There were 124 falling cases (32 in hurdling and 92 in steeplechasing) identified. The injury risk of fallers was 8.9% and fatality risk 6.5%. Duration of journey to the racecourse, behaviour in the parade ring and weather at the time of the race were associated with falling in both hurdle and steeplechase racing. Age, amount of rainfall and going were also associated with falling in steeplechase racing. CONCLUSIONS: Falls at fences are significant contributors to equine fatalities during NH racing. Potentially modifiable risk factors identified were the condition of track surfaces and journey time to the racecourse. POTENTIAL RELEVANCE: It is hoped that information from this study may be used in future interventions to improve horse and jockey safety in racing. The study has also identified areas requiring further research, such as equine behaviour and its effect on racing performance, and the effect of light conditions on jumping ability.     

Incidence and risk factors associated with exertional rhabdomyolysis syndrome in National Hunt racehorses in Great Britain

A telephone survey of 51 National Hunt racing yards with 1140 horses in training was made in April and May 2003 to establish the incidence of exertional rhabdomyolysis syndrome during the previous year. A case-control study was used to investigate the risk factors for the syndrome in eight yards selected on the basis that cases had been confirmed by the analysis of serum muscle enzymes. The overall incidence of syndrome was 6.1 cases per 100 horses per year, and 55 per cent of the yards reported at least one case. The risk factors identified were sex, the average length of the training gallop, and the type of horse (steeplechaser, bumper/unraced or hurdler). There were no significant associations with the horses' temperament, age or Timeform rating.     

Musculoskeletal injuries in Thoroughbred racehorses: A study of three large training yards in Newmarket, UK (2005–2007)

Musculoskeletal injury is the most common cause of lost training days in the young Thoroughbred horse in flat race training. To date, there has been little investigation of the regional patterns of injury frequently observed by clinicians in racehorse practice. The present study was conducted to determine incidence of musculoskeletal injuries in Thoroughbreds in training in Newmarket, United Kingdom. Veterinary records for all horses resident in three large (>100 horse) training yards were assessed for occurrence of significant musculoskeletal injury.A total of 248 injuries were recorded in 217 individual horses, from a total population of 616 individual horses; fractures of the tibia (20.7%) and proximal phalanx (14.5%) were the most common. Overall injury rates were similar between yards (23–26%/year), with seasonal patterns noted for some injury types. Incidence of certain injuries (P1, metacarpal/metatarsal condylar, pelvic fractures, and superficial digital flexor tendonitis) varied between yards. The majority of carpal, P1 fracture and SDF tendonitis cases were right-sided.     

Characteristics of Thoroughbred and Quarter Horse racehorses that sustained a complete scapular fracture

Reasons for performing study: To determine if scapular fractures occur in racehorses with distinctive characteristics. Objectives: To test the hypothesis that Thoroughbred (TB) and Quarter Horse (QH) racehorses with a scapular fracture have similar characteristics that are different from those of their respective racetrack populations. Methods: Necropsy findings, case details, last race information and career earnings for TB and QH racehorses that had a scapular fracture in California between 1990 and 2008 were retrospectively compared between breeds. Horse signalment, career earnings, career starts and race characteristics were obtained for all California racehorses. Comparisons were made between affected horses, other racehorses that died, and all horses that raced, in California during the 19 year period. Results: Seventy‐three TB and 28 QH racehorses had a similar, complete comminuted scapular fracture with an articular component, and right forelimb predilection. The QHs had a higher incidence of scapular fracture incurred during racing than TBs (0.98 vs. 0.39/1000 starters). The TB and QH incident rates for musculoskeletal deaths incurred racing were 20.5 and 17.5/1000 starters, respectively; however, a greater proportion of TB musculoskeletal deaths occurred training (40% vs. 8%). Horses with a scapular fracture were more likely to be male and aged 2 or ≥5 years than the racetrack population. Most affected QHs (64%) were 2‐year‐olds; most TBs (74%) were aged ≥3 years. Scapular fractures occurred more commonly during racing in QHs (70%) than TBs (44%). Race‐related scapular fracture was more likely to occur in a Maiden race than in a non‐Maiden race. Horses with a scapular fracture had fewer career starts than the racetrack population. Conclusions and potential relevance: Despite breed differences for signalment and exercise distances, both breeds incur a complete scapular fracture that is more likely to occur in the right scapula of young and older, male racehorses, early in their race career or after few races. Quarter Horses sustain a catastrophic scapular fracture more frequently than TBs.     

A survey of racing injuries in the Greyhound

A survey was made of a total of 786 reported injuries in racing Greyhounds during 1968. The most common sites of injury are identified and the results compared with existing data (and clinical experience).     

Effect of tracheal mucus and tracheal cytology on racing performance in Thoroughbred racehorses

REASON FOR PERFORMING STUDY: Accumulations of mucus within the trachea are often found during endoscopic examinations of the airways of poorly performing racehorses, but the clinical importance of this finding is unknown. OBJECTIVES: To determine the effect of tracheal mucus, pharyngeal lymphoid hyperplasia (PLH) and cytological indices of tracheal aspirate on racing performance in Thoroughbred horses assessed by race place and whether the horse was raced. METHODS: Endoscopic examination of the nasopharynx, larynx and trachea was performed, and a tracheal aspirate obtained monthly at Thistledown racetrack from April to December, 2002 and 2003. Horses received a score of 0-4 for the degree of PLH and 0-4 for the amount of mucus visible in the trachea. The tracheal aspirate was assessed for turbidity, and total and differential cell counts. Generalised estimating equations models were used as repeated measures models for each risk factor and the level of association assessed through the risk factor's P value in the model. RESULTS: Moderate to severe tracheal mucus (2-4) was a risk factor for poor racing performance. There was no association between degree of PLH, cell counts or turbidity of tracheal wash fluid and racing performance. However, horses that raced had higher total neutrophil counts in tracheal wash aspirates than horses that did not race. CONCLUSIONS: Grades 2-4 tracheal mucus should be considered a potential cause of poor racing performance in Thoroughbred horses. CLINICAL RELEVANCE: Because moderate to severe tracheal mucus accumulation, and not increased tracheal neutrophils, was a risk factor for poor racing performance, functionally significant airway inflammation may best be confirmed by the presence of mucus rather than increased number of neutrophils in the trachea.