Frequency of and risk factors for epistaxis associated with exercise-induced pulmonary hemorrhage in horses: 251,609 race starts (1992-1997)

Field-training in young two-year-old thoroughbreds: investigating cardiorespiratory adaptations and the presence of exercise induced pulmonary hemorrhage

BACKGROUND

Comparatively little is known regarding the initial cardiorespiratory response of young racehorses to training. The objectives were to compare physiological parameters before and after introductory training and determine whether young Thoroughbreds show endoscopic signs of exercise-induced pulmonary hemorrhage (EIPH). Ten Thoroughbreds (20-23 months) underwent 12-weeks of introductory training, including weekly speed sessions. Two 600 m high-speed exercise tests (HSET) were performed following weeks 4 and 12 while wearing a validated ergospirometry facemask. Peak oxygen consumption (V̇O2pk) and ventilatory parameters (tidal volume, VT; peak inspiratory and expiratory flow, PkV̇I, PkV̇E; respiratory frequency, Rf; minute ventilation, V̇E) were measured. The ventilatory equivalent of oxygen (V̇E/V̇O2) and the aerobic and anaerobic contributions to energy production were calculated. Maximal heart rate (HRmax) and HR at maximal speed (HRVmax) were determined. Post-exercise hematocrit, plasma ammonia and blood lactate were measured. Evidence of EIPH was investigated via tracheobronchoscopy post-exercise. Results were compared (paired t-test, P < 0.05).

RESULTS

Horses were faster following training (P < 0.001) and V̇O2pk increased 28 ml/(kg total mass.min) (28 ± 16%; P < 0.001). Ventilatory (V̇E, P = 0.0015; Rf, P < 0.001; PkV̇I, P < 0.001; PkV̇E, P < 0.001) and cardiovascular parameters (HRmax, P = 0.03; HRVmax, P = 0.04) increased. The increase in V̇E was due to greater Rf, but not VT. V̇E/V̇O2 was lower (26 ± 3.6 vs 23 ± 3.7; P = 0.02), indicating improved ventilatory efficiency. Anaerobic contribution to total energy production increased from 15.6 ± 6.1% to 18.5 ± 6.3% (P = 0.02). Post-exercise hematocrit (P < 0.001), plasma ammonia (P = 0.03) and blood lactate (P = 0.001) increased following training. Horses showed no signs of EIPH.

CONCLUSIONS

Young two-year-old Thoroughbreds responded well to introductory training without developing tracheobronchoscopic evidence of EIPH.

Risk Factors for Epistaxis in Thoroughbred Flat Races in Japan (2001-2020)

We investigated the risk factors for epistaxis in Japanese flat races over a 20-year period. The veterinary records of horses identified as having epistaxis by endoscopy on the race day, and the official racing records of all flat races from April to September between 2001 and 2020, were reviewed. The racecourses (n = 10), surface type, surface condition, race class, race distance, race year, sex, age, two training centers, ambient temperature, and body weight on race days were assessed using multivariable logistic regression (p < 0.05). Of 475,709 race starts, 616 (1.30 cases per 1000 starts; 95% confidence interval [CI], 1.20-1.40) included an epistaxis event. Nine variables were significantly associated with epistaxis. Seven of the variables have been reported in previous studies: lower ambient temperature, soft surface conditions, shorter racing distances (≤1400 m), increasing age, females and geldings compared to males, training center, and race year. However, two novel variables were identified as significantly associated with epistaxis, increasing body weight per 20 kg (p < 0.001, odds ratio [OR], 1.33; 95% CI, 1.25-1.41) and the racecourses that the horses were running at (p < 0.001, especially Sapporo [OR; 4.74, 95% CI, 3.07-7.31], Hakodate [OR, 4.66; 95% CI, 3.05-7.11], and Kokura [OR, 4.14; 95% CI, 2.65-6.48] compared to the reference racecourse [Kyoto]). These results can facilitate developing interventions to reduce epistaxis in flat racing.

Risk Factors for Exercise-Associated Sudden Cardiac Death in Thoroughbred Racehorses

Cardiac arrhythmias resulting in sudden cardiac death (SCD) are an important cause of racehorse fatalities. The objective of this study was to determine risk factors for SCD in Thoroughbreds by evaluating a sample with a policy of mandatory post-mortem following racing or training fatalities. Risk factors were compared between case horses with SCD (n = 57) and control horses with other fatal injury (OFI, n = 188) by univariable and multivariable logistic regression. Survival in years for horses with SCD was compared to OFI using the Kaplan−Meier method with log rank test. The following variables were most important in the multiple logistic model: Horses with SCD were more likely to die during training than during racing, SCD (42/57, 74%) vs. OFI (82/188, 44%; odds ratio [OR], 95% confidence interval [CI], 2.5, 1.2−5.4; p = 0.01), had fewer lifetime starts, median (interquartile range [IQR]), SCD (3.0 [0.0−9.0]) vs. OFI (9.0 [0.0−22.8]; OR, 95% CI, 0.96, 0.9−1.0; p = 0.02 and were less likely to be entire (uncastrated) males, SCD 9/57 (16%) vs. OFI (46/188, 25%; OR, 95% CI, 0.47, 0.1−0.9; p = 0.03). Survival in years (median (IQR)) for horses with SCD was 3.6 (3.1−4.4), which was shorter than OFI (4.5 [3.1−6.0], hazard ratio, 95%CI, 1.6,1.2−2.3; p < 0.001). SCD occurs more commonly in training than racing, which suggests exercise intensity is less important in precipitating this fatality. In this study, SCD occurred early in the careers of affected horses.

Associations between Exercise-Induced Pulmonary Hemorrhage (EIPH) and Fitness Parameters Measured by Incremental Treadmill Test in Standardbred Racehorses

Simple Summary

Exercise-induced pulmonary hemorrhage (EIPH) frequently affects racehorses worldwide and has been widely associated with poor performance; however, scientific evidence supporting this observation is low. The present retrospective study aims to evaluate objectively whether the presence and grade of EIPH could affect some fitness parameters, measured during an incremental treadmill test, in poorly performing Standardbred racehorses. For this purpose, the association between EIPH and the results of a treadmill metabolic test (including blood lactate analysis and venous blood gas analysis) were evaluated in 81 Standardbred racehorses. No relationship between EIPH and aerobic/anaerobic capacity was observed, suggesting that EIPH may affect performance in a different manner. However, EIPH-affected horses were shown to reach higher hematocrit values during exercise compared to EIPH-negative horses; therefore, it may be hypothesized that hemoconcentration may take part in the pathogenesis of EIPH by increasing the pulmonary capillary pressure.

Abstract

Exercise-induced pulmonary hemorrhage (EIPH) is a condition affecting up to 95% of racehorses, diagnosed by detecting blood in the trachea after exercise and/or the presence of hemosiderophages in the bronchoalveolar lavage fluid (BALf). Although EIPH is commonly associated with poor performance, scientific evidence is scarce. The athletic capacity of racehorses can be quantified through some parameters obtained during an incremental treadmill test; in particular, the speed at a heart rate of 200 bpm (V200), and the speed (VLa4) and the heart rate (HRLa4) at which the blood lactate concentration reaches 4 mmol/L are considered good fitness indicators. The present retrospective study aims to evaluate whether EIPH could influence fitness parameters in poorly performing Standardbreds. For this purpose, data from 81 patients regarding their V200, VLa4, HRLa4, peak lactate, maximum speed, minimum pH, and maximum hematocrit were reviewed; EIPH scores were assigned based on tracheobronchoscopy and BALf cytology. The association between the fitness parameters and EIPH was evaluated through Spearman’s correlation analysis. No relationship between EIPH and V200, VLa4, and HRLa4 was observed. Interestingly, EIPH-positive horses showed higher hematocrit values (p = 0.0072, r = 0.47), suggesting the possible influence of the hemoconcentration on the increase of pulmonary capillary pressure as a part of the pathogenesis of EIPH.

Training related risk factors for exercise induced pulmonary haemorrhage in British National Hunt racehorses

BACKGROUND

Exercise induced pulmonary haemorrhage (EIPH) is an important condition of horses performing high intensity exercise, with reported prevalence among racehorses of up to 95%, based on the detection of blood on tracheobronchoscopy. Previously identified risk factors include age, sex, season, race type, years spent in racing and lower airway inflammation.

OBJECTIVES

To estimate the prevalence of EIPH in British National Hunt racehorses as indicated by two outcome measures: presence of tracheal blood on tracheobronchoscopy, and presence of moderate-large (significant) proportions of haemosiderophages in tracheal wash (TW) fluid; and to identify training-related risk factors for these indicators of EIPH.

STUDY DESIGN

Prospective longitudinal study.

METHODS

Data from tracheobronchoscopy and TW cytology were analysed using univariable and multivariable mixed-effects logistic regression.

RESULTS

1184 observations, from 177 horses, were analysed. The prevalence of tracheal blood was 7.2% (95%CI: 5.8, 8.8) and significant haemosiderophages in TW fluid was 36% (95%CI: 33.3, 38.8). Increased time in training was significantly associated with increased odds of EIPH. For each additional year spent in training the odds of tracheal blood and presence of significant proportions haemosiderophages increased approximately 1.5-fold (OR = 1.5; 95%CI: 1.1-2.0; P = .005; and OR = 1.5; 95%CI: 1.3, 1.8; P < .001, respectively). Current inflammation was associated with previous haemorrhage, but not current haemorrhage.

MAIN LIMITATIONS

There are no standardised measures for quantification of TW cytological parameters for EIPH diagnosis. Few horses were examined following jumping. Recent racing dates were not included in analysis.

CONCLUSIONS

Increasing time in training was a risk factor for both indicators of EIPH. Current inflammation was associated with previous haemorrhage, but not current or future haemorrhage, suggesting that haemorrhage leads to inflammation but not that inflammation leads to haemorrhage. Overall, our findings are consistent with the capillary stress failure theory of EIPH. The development of standardised measures for TW cytological diagnosis of EIPH is warranted.

Results of racetrack examinations of Standardbred horses at race meetings in New South Wales

This study analysed the race day veterinary reports from harness racing meetings controlled by the New South Wales Greyhound and Harness Racing Regulatory Authority between 1 September 2008 and 30 June 2009. The findings of all prerace and postrace examinations were analysed, and the frequency of observations was recorded. Chi-square testing was used to determine whether the incidence of abnormalities differed between age groups and tracks. A total of 542 meetings were conducted during the period of the study, with veterinary examinations conducted at 395 of these meetings. A total of 520 veterinary examinations (60 prerace and 460 postrace) were conducted. During the period of the study, 3685 horses started 31,393 times. Injuries occurring during the warm-up or start were the most common finding on prerace examination (11 reports) followed by lameness (6 reports). Lameness was the most common problem identified during postrace examinations, occurring at a rate of 2.10 cases per 1000 starts. Other problems identified at a rate of more than 1 per 1000 starts were poor postrace recovery/heat stress (2.04) and lacerations (1.75). Falls occurred at a rate of 1.72 cases per 1000 starts. Two-year-old horses were less likely to be lame than 3, 5 and 6-year-old horses. There was no difference in the rate of falls or lameness between tracks. This study provides a benchmark against which ongoing improvements in welfare can be assessed.

Exercise-induced Pulmonary Hemorrhage: Is It Important and Can It Be Prevented?

Exercise-induced pulmonary hemorrhage (EIPH) occurs commonly in horses undergoing strenuous exercise. Reported risk factors include racing in cold temperatures and wearing of bar shoes. In horses with documented moderate to severe EIPH, increasing the interval between races and adopting a negative race pace strategy may reduce the severity of EIPH in subsequent races. EIPH seems to have an impact on performance only when moderate to severe. This occurs in a small number of starters, approximately 6%. EIPH often is erratic in severity from race to race, although across a population it is weakly progressive over increasing race starts.

Risk factors for race-day fatality, distal limb fracture and epistaxis in Thoroughbreds racing on all-weather surfaces in Great Britain (2000 to 2013)

The incidence of race-day injuries in Great Britain (GB) is higher on all-weather (AW) surfaces than on turf. However, to date no studies have focused on identifying risk factors for injury specific to AW racing. Therefore, the objective of the current study was to determine risk factors for fatality, distal limb fracture (DLF) and episodes of epistaxis in flat racing Thoroughbreds racing on AW surfaces in GB. Data included all flat racing starts on AW surfaces (n=258,193) and race-day veterinary events recorded between 2000 and 2013. Information on additional course-level variables was gathered during face-to-face interviews with racecourse clerks. Horse-, race- and course-level risk factors for each outcome were assessed using mixed-effects multivariable logistic regression including horse as a random effect. A classification tree method was used to identify potential interaction terms for inclusion in the models. During the study period, there were 233 fatalities resulting in a fatality incidence of 0.90 per 1000 starts; 245 DLF with a resultant DLF incidence of 0.95 per 1000 starts and 410 episodes of epistaxis resulting in an epistaxis incidence of 1.59 per 1000 starts. Risk factors varied for each outcome, although some factors were similar across models including the going, racing intensity, horse age, age at first race start, 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, albeit with an interaction between the two variables in the fatality model. Faster going increased the odds of epistaxis and DLF but not fatality. Increasing race distance increased the odds of fatality but reduced the odds of epistaxis. Epistaxis was associated with type of AW surface (Fibresand versus Polytrack^®), but DLF and fatality were not. This study provides further evidence of the association between the risk of race-day injuries and fatalities and current age, age at first start, race distance, going and horse performance. These findings provide the racing industry with information to develop strategies to reduce the occurrence of race-day events on AW surfaces.

Exercise-induced pulmonary hemorrhage: where are we now?

As the Thoroughbreds race for the final stretch, 44 hooves flash and thunder creating a cacophony of tortured air and turf. Orchestrated by selective breeding for physiology and biomechanics, expressed as speed, the millennia-old symphony of man and beast reaches its climax. At nearly 73 kilometers per hour (45 mph) over half a ton of flesh and bone dwarfs its limpet-like jockey as, eyes wild and nostrils flaring, their necks stretch for glory. Beneath each resplendent livery-adorned, latherin-splattered coat hides a monstrous heart trilling at 4 beats per second, and each minute, driving over 400 L (105 gallons) of oxygen-rich blood from lungs to muscles. Matching breath to stride frequency, those lungs will inhale 16 L (4 gallons) of air each stride moving >1,000 L/min in and out of each nostril - and yet failing. Engorged with blood and stretched to breaking point, those lungs can no longer redden the arterial blood but leave it dusky and cyanotic. Their exquisitely thin blood-gas barrier, a mere 10.5 μm thick (1/50,000 of an inch), ruptures, and red cells invade the lungs. After the race is won and lost, long after the frenetic crowd has quieted and gone, that blood will clog and inflame the airways. For a few horses, those who bleed extensively, it will overflow their lungs and spray from their nostrils incarnadining the walls of their stall: a horrifically poignant canvas that strikes at horse racing's very core. That exercise-induced pulmonary hemorrhage (EIPH) occurs is a medical and physiological reality. That every reasonable exigency is not taken to reduce/prevent it would be a travesty. This review is not intended to provide an exhaustive coverage of EIPH for which the reader is referred to recent reviews, rather, after a brief reminder of its physiologic and pathologic bases, focus is brought on the latest developments in EIPH discovery as this informs state-of-the-art knowledge, the implementation of that knowledge and recommendations for future research and treatment.

Exercise induced pulmonary hemorrhage in horses: American College of Veterinary Internal Medicine consensus statement

Background

Published studies of exercise‐induced pulmonary hemorrhage (EIPH), when assessed individually, often provide equivocal or conflicting results. Systematic reviews aggregate evidence from individual studies to provide a global assessment of the quality of evidence and to inform recommendations.

Objectives

Evaluate evidence to determine: if EIPH adversely affects the health, welfare or both of horses; if EIPH affects the athletic capacity of horses; the efficacy of prophylactic interventions for EIPH; and if furosemide affects the athletic capacity of horses.

Animals

None.

Materials and Methods

Systematic review. A panel of 7 experts was formed to assess evidence in the peer reviewed literature addressing each of the 4 objectives. Methodology followed that of the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE). Publications were assessed for quality of evidence by working groups of the panel, and a summary of findings was presented in tables. Recommendations were based on quality of evidence and were determined by a vote of the panel.

Results

Much of the evidence was of low to very low quality. Experimental studies frequently lacked adequate statistical power. There was moderate to high quality evidence that EIPH is progressive, is associated with lung lesions, that it adversely affects racing performance, that severe EIPH (Grade 4) is associated with a shorter career duration, that furosemide is efficacious in decreasing the incidence and severity of EIPH, and that administration of furosemide is associated with superior race performance.

Conclusions and clinical significance

Strong recommendation that EIPH be considered a disease and a weak recommendation for use of furosemide in management of racehorses with EIPH.

Exercise-induced pulmonary haemorrhage in horses – review

Exercise-induced pulmonary haemorrhage is a major cause of poor performance in the equine athlete. It is an important cause of exercise intolerance and results from strenuous exercise and pathophysiological changes in the equine lung and possibly in the airways. Endoscopic surveys of the respiratory tracts of horses after competitive events have shown that many horses experience exercise-induced pulmonary haemorrhage. The reported incidence of exercise-induced pulmonary haemorrhage in different breeds varies between 40–85%. The cause of bleeding in exercising horses has fostered considerable debate over the past three centuries, but currently, the most accepted hypothesis is that the source of haemorrhage is disruption of the pulmonary capillaries during exercise. Furosemide is the medication used most widely for the treatment and prevention of exercise-induced pulmonary haemorrhage. This review provides an update on the aetiology, clinical signs, physiopathology, diagnosis and treatment of exercise-induced pulmonary haemorrhage.

Epistaxis in racehorses: risk factors and effects on career

OBJECTIVE

To profile Thoroughbreds that incurred a ban under Australian Rule of Racing 53A on New South Wales racetracks between August 1999 and July 2008, determine the effect on their careers and identify the factors that predict whether these horses would race again or experience a recurrence of epistaxis.

METHODS

Differences between horses that did or did not return to racing and did or did not suffer recurrent epistaxis were determined. Backwards stepwise logistic regression was used to identify variables predicting a return to racing and recurrence of epistaxis.

RESULTS

The mean (± SD) age at the first episode of epistaxis was 4.90 ± 1.28 years. Males that bled were older, had more career starts and were more likely to race again than females. Horses that were retired from racing after the first episode of epistaxis were older than horses that continued to race. Variables that were significant predictors of retirement were: age at the first episode of epistaxis, sex, percentage of winning starts before the first episode of epistaxis, percentage of placed starts before the first episode of epistaxis and number of starts in the preparation before the first episode of epistaxis. The significant predictors of recurrence of epistaxis were: change in distance between previous start and start at which the second episode occurred and a change in percentage of winning starts, although the odds ratios were low (0.98-0.99).

CONCLUSIONS

Females experience epistaxis at a younger age than males. No readily applicable predictors of the recurrence of epistaxis were identified.

Respiratory diseases and their effects on respiratory function and exercise capacity

Given that aerobic metabolism is the predominant energy pathway for most sports, the respiratory system can be a rate-limiting factor in the exercise capacity of fit and healthy horses. Consequently, respiratory diseases, even in mild forms, are potentially deleterious to any athletic performance. The functional impairment associated with a respiratory condition depends on the degree of severity of the disease and the equestrian discipline involved. Respiratory abnormalities generally result in an increase in respiratory impedance and work of breathing and a reduced level of ventilation that can be detected objectively by deterioration in breathing mechanics and arterial blood gas tensions and/or lactataemia. The overall prevalence of airway diseases is comparatively high in equine athletes and may affect the upper airways, lower airways or both. Diseases of the airways have been associated with a wide variety of anatomical and/or inflammatory conditions. In some instances, the diagnosis is challenging because conditions can be subclinical in horses at rest and become clinically relevant only during exercise. In such cases, an exercise test may be warranted in the evaluation of the patient. The design of the exercise test is critical to inducing the clinical signs of the problem and establishing an accurate diagnosis. Additional diagnostic techniques, such as airway sampling, can be valuable in the diagnosis of subclinical lower airway problems that have the capacity to impair performance. As all these techniques become more widely used in practice, they should inevitably enhance veterinarians' diagnostic capabilities and improve their assessment of treatment effectiveness and the long-term management of equine athletes.

The effect of sildenafil citrate administration on selected physiological parameters of exercising Thoroughbred horses

REASONS FOR PERFORMING STUDY

Sildenafil, a phosphodiesterase-5 inhibitor vasodilator, increases cGMP concentrations by inhibiting enzymatic degradation. Marketed to treat erectile dysfunction in men, it also reduces pulmonary arterial pressure (PAP). Because it reduces PAP, sildenafil may enhance performance and/or prevent exercise induced-pulmonary haemorrhage (EIPH).

OBJECTIVE

To determine if sildenafil citrate administration altered commonly measured indices of performance or reduced EIPH in exercised horses.

METHODS

Thirteen athletically conditioned Thoroughbred horses (2 mares and 11 geldings, age 3-12 years) were administered sildenafil citrate or placebo in 2 crossover design exercise testing studies. In a step-wise test to exhaustion, inspired/expired gas analysis, blood lactate, heart rate, runtime and bronchoalveolar lavage (BAL) cytology were measured. In a 13 m/s test to exhaustion, blood lactate, heart rate, runtime, BAL cytology and pulmonary arterial pressure were measured. Data were analysed with paired and unpaired t tests, one-way ANOVA and Tukey's pair-wise multiple comparison and Friedman repeated measure analysis of variance on ranks.

RESULTS

The administration of sildenafil did not alter mean inspired/expired gas measurements, plasma lactate concentrations or acute pulmonary haemorrhage in either exercise test or pulmonary arterial pressure measurement in the 13 m/s trial. Heart rates in both stress tests were significantly different at submaximal speeds and during the early recovery period. Run time was not affected by sildenafil administration in the step-wise trial (P = 0.622) or in the 13 m/s trial (P = 0.059).

CONCLUSIONS

Sildenafil did not alleviate pulmonary haemorrhage or enhance performance-related indices in these trials. Sildenafil administration altered cardiovascular adaptation to intense exercise as evidenced by altered heart rates at submaximal speeds and post exercise. The effect of these alterations on other performance perimeters was not evident.

Evaluation of race distance, track surface and season of the year on exercise-induced pulmonary haemorrhage in flat racing Thoroughbreds in Brazil

REASONS FOR PERFORMING STUDY

To our knowledge no studies evaluating risk factors to EIPH have been undertaken with such a population of horses in Brazil, which is one of the few countries in the racing community to accept the use of frusemide (FUR) as a prerace medication for bleeders. We also compared national results with those already in the literature.

OBJECTIVES

To verify the influence of variables such as distance of the race, racetrack surface, going and season of the year in the recurrence and severity of EIPH and its effect on the finishing position of flat racing Thoroughbreds in Brazil.

METHODS

2118 post race respiratory endoscopies were recorded, in a total of 1003 individual horses. All horses in the study were certified bleeders (deemed positive by registered veterinarians following one or more endoscopies) and were administered FUR prior to each race. Data was analysed using both ordinary logistic regression and multiple logistic regression.

RESULTS

The results suggest that race distance, season of the year and racetrack surface affect the recurrence of EIPH. Also, despite the use of FUR, the majority (62%) of horses continued to display some degree of haemorrhage.

CONCLUSIONS

There was a tendency for horses that remained positive despite the use of FUR to finish unplaced in a race. Horses which had a significant reduction in bleeding and became HPIE negative after the use of FUR, tended to finish in top positions. It was not possible to determine a pattern of severity of EIPH in horses with more than one endoscopy. Further studies are required to improve our understanding of this syndrome and its correlations to performance in the racing Thoroughbred, together with the role of FUR and its possible enhancing performance effects and efficacy in consistently diminishing EIPH.

POTENTIAL RELEVANCE

This study enabled a better understanding of the use of FUR in Brazilian Thoroughbred racehorses and showed there was a tendency towards improvement in performance after administrion of FUR in bleeders. The fact that a large number of horses remained positive for EIPH despite the use of FUR should encourage the scientific community to search for better ways of reducing, or preventing, this syndrome.

Risk factors for epistaxis on British racecourses: evidence for locomotory impact-induced trauma contributing to the aetiology of exercise-induced pulmonary haemorrhage

REASONS FOR PERFORMING STUDY

The proposed biological mechanisms for exercise-induced pulmonary haemorrhage (EIPH) are many and varied. Better knowledge of risk factors should lead to achievable measures to reduce the incidence.

OBJECTIVES

To identify risk factors associated with epistaxis following racing in UK Thoroughbreds, to gain possible insights into the pathogenesis of the condition and to investigate the association between epistaxis and race finishing position.

METHODS

The association of epistaxis occurring on UK racecourses between 1996 and 1998 with a wide range of race-, horse- and start-level variables was examined in multivariable mixed effect logistic regression analyses. Four multivariable analyses were conducted, one for all race types considered collectively and one each for flat, hurdle and steeplechase race types considered separately.

RESULTS

Risk of epistaxis was significantly increased for hurdle and steeplechase race types compared to both flat and National Hunt flat races. In 3 of the 4 final models, there was a significant biological trend for increasing risk of epistaxis with increasing ground hardness ('going') and accumulated years spent racing. However, in flat races epistaxis was such a rare outcome (0.33 cases per 1000 starts) that this subset analysis had insufficient power to measure the detectable effect of 'going' as statistically significant. Horses with epistaxis were significantly more likely to have a poorer finishing position than those without blood at the nostrils.

CONCLUSIONS

Findings were consistent with the theory that locomotory impact-induced trauma contributes to exercise-induced epistaxis. Further validation of this hypothesis through application of similar methods to endoscopically visible EIPH and through biomechanical studies is warranted.

POTENTIAL RELEVANCE

Knowledge of significant risk factors should allow formulation of practical measures, such as track watering, to reduce the risks of EIPH and epistaxis in racehorses.

A Direct Enzyme Immunoassay for the Measurement of Furosemide in Horse Plasma

A new enzyme immunoassay (EIA) for the measurement of furosemide in horse plasma is described. The lower limit of detection of this EIA method was 7.8 ng/ml. The intra-and inter-assay coefficients of variation ranged from 2.5% to 4.9% and 7.5% to 9.8%, respectively. Cross-reactivity with other compounds was not observed. There was a high correlation (r2=0.987) between the high-performance liquid chromatography and EIA results obtained for furosemide concentrations in horse plasma. These results indicate that the newly developed EIA method is useful for the quantitative analysis of furosemide in horse plasma.

Association between exercise-induced pulmonary hemorrhage and performance in Thoroughbred racehorses

OBJECTIVE

To determine whether exercise-induced pulmonary hemorrhage (EIPH) was associated with racing performance inThoroughbred horses not medicated with furosemide and not using nasal dilator strips.

DESIGN

Observational cross-sectional study.

ANIMALS

744 two- to 10-year-old Thoroughbred horses racing in Melbourne, Australia.

PROCEDURE

Horses were enrolled prior to racing, and a tracheobronchoscopic examination was performed after 1 race. Examinations were recorded on videotape, and presence and severity (grade 0 to 4) of EIPH were subsequently determined by 3 observers blinded to the horses' identity. Race records were abstracted for each horse examined.

RESULTS

Overall, 52.1% of horses eligible for participation in the study were examined, and horses that were examined did not differ from horses that were not examined in regard to age, sex distribution, or proportion of horses that won or finished in the first 3 positions. Horses with EIPH grades < 1 were 4.0 times as likely to win, 1.8 times as likely to finish in the first 3 positions, and 3.03 times as likely to be in the 90th percentile or higher for race earnings as were horses with grades > 2. Horses with EIPH grades > 1 finished significantly farther behind the winner than did horses without EIPH. However, odds that horses with grade 1 EIPH would win or finish in the first 3 positions were not significantly different from odds for horses without EIPH.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that EIPH is associated with impaired performance in Thoroughbred racehorses not medicated with furosemide and not using nasal dilator strips.

Risk factors and prevalence of injuries in horses during various types of steeplechase races

OBJECTIVE

To identify the types of injuries sustained by horses that competed in steeplechase races and determine the prevalence of and risk factors for those injuries.

DESIGN

Prospective study.

ANIMALS

2,680 horses that competed in various types of steeplechase races from 1996 through 2000.

PROCEDURE

Data regarding races; environment; equipment problems; the number of horses that entered, started, and finished races; the number of riders that fell; and the number of horses that were slowed or stopped by the rider, ran off the course, fell, and sustained injuries or physical abnormalities during races were collected on a standard form by the official veterinarian who attended each meet. Data from all meets were not recorded; however, in recorded meets, data from every race were reported.

RESULTS

Data for 197 hurdle, 65 timber, 76 flat, and 8 mixed races were recorded. Nine (3.4/1,000 horses that started in races) horses died or were euthanatized, and 7 of those were associated with catastrophic musculoskeletal injury. Seven fractures were recorded. Four fractures involved forelimbs, 1 involved a hind limb, and 2 involved the cervical portion of the vertebral column. All horses with fractures were euthanatized. Deep or hard course conditions were associated with an increased risk of breakdown injuries.

CONCLUSIONS AND CLINICAL RELEVANCE

Successful development and implementation of strategies to prevent injuries and death in horses in steeplechase races depend on a clear understanding of the types and prevalence of injuries involved and risk factors associated with those injuries.

Risk factors for atrial fibrillation during racing in slow-finishing horses

OBJECTIVE

To determine prevalence of atrial fibrillation (AF) immediately after racing among racehorses that finished well behind the winners and examine potential risk factors for AF in these horses.

DESIGN

Case-control study.

ANIMALS

39,302 racehorses representing 404,090 race starts in races sanctioned by the Japan Racing Association between 1988 and 1997.

PROCEDURE

Horses that finished > or = 4 (turf races) or 5 (dirt races) seconds behind the winner or that did not complete the race were examined for AF within 5 minutes after the race. Logistic regression and chi2 analyses were used to determine whether sex, age, race distance, race surface, year, or development of epistaxis was associated with development of AF.

RESULTS

Estimated minimum frequency of AF was 0.03% (123 instances of AF following 404,090 race starts), and estimated minimum prevalence of AF among racehorses was 0.29% (115 horses with AF among 39,302 racehorses). Estimated frequency of AF among horses that finished slowly or did not finish was 1.39% (120 instances of AF among 8,639 examinations), and estimated prevalence of AF in horses that finished slowly was 1.23% (92 instances of AF among 7,500 horses) or 1.01% when only the first time a horse finished slowly was considered (76 instances of AF among 7,500 horses). Atrial fibrillation was paroxysmal in most horses. Among horses that finished slowly, 4-year-old and older horses and horses that raced on turf were more likely to develop AF.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that the likelihood of AF among racehorses that finish slowly is related to age and racing surface.

Exercise-induced pulmonary hemorrhage

EIPH is a condition affecting virtually all horses during intense exercise worldwide. The hemorrhage originates from the pulmonary vasculature and is distributed predominantly bilaterally in the dorsocaudal lung lobes. As the condition progresses, the lung abnormalities extend cranially along the dorsal portions of the lung. An inflammatory response occurs in association with the hemorrhage and may contribute to the chronic sequela. Although conflicting opinions exist as to its affect on performance, it is a syndrome that is thought to increase in severity with age. The most commonly performed method to diagnose EIPH at the present time is endoscopy of the upper airway alone or in combination with tracheal wash analysis for the presence of erythrocytes and hemosiderophages. Because horses may not bleed to the same extent every time and the bleeding may originate from slightly different locations, these diagnostic procedures may not be extremely sensitive or quantitative. At this time, there is no treatment that is considered a panacea, and the currently allowed treatments have not proven to be effective in preventing EIPH. Future directions for therapeutic intervention may need to include limiting inflammatory responses to blood remaining within the lungs after EIPH.

Heterogeneity of intrapleural pressures during exercise

We determined whether the caudodorsal region of the intrapleural space in exercising horses experiences larger pressure fluctuations than other regions and whether systematic phase-shifting of peak intrapleural pressures along the length of the thorax suggests the existence of locomotor-induced intrapleural pressure waves. We utilised percutaneous introducers and solid-state pressure-tip transducers implanted along the dorsal aspect of the thorax, mid-thorax or oesophagus to measure regional intrapleural pressures while 3 horses galloped on a flat treadmill at 13-14 m/s, then recorded pressures from the same catheters when horses exercised intensely (heart rate 170-190 beats/min) while swimming with no ground concussion. Pressure excursions in the caudodorsal region did not vary systematically from other regions during galloping or swimming, nor more than a few torr between different locations. During swimming, peak expiratory pressures were higher than during galloping (68-79 vs. 26-32 torr), and horses breathed explosively at frequencies 5 times slower than while galloping (28 vs. 120/min). During galloping, individual catheter locations registered locomotor concussion; however, this was variable and did not indicate a systematic pressure wave passing through the lung or intrapleural space.