The prevalence and anatomical distribution of equine gastric ulceration syndrome (EGUS) in 201 horses in Denmark

Reasons for performing study: The prevalence (up to 93% in Thoroughbred racehorses) and severity of equine gastric ulceration syndrome (EGUS) have been correlated with the type of training and associated management practices. However, there have been few reports to confirm these findings in nonracehorses in Europe. Objectives: To describe the prevalence, anatomical distribution, severity and number of gastric ulceration lesions in a population of Danish pleasure horses; and to investigate differences for groups based on age, breed type and workload. Methods: A total of 201 horses not in active race‐training, age 7 months‐27 years, were evaluated, representing 23 different stables from all 5 regions of Denmark. These horses were considered to be healthy by the owner and not on veterinary treatment for EGUS. Endoscopically observed ulcer lesion scores were based on the number present (0–4) and severity (0–5). The presence or absence of ulcers in the glandular and/or nonglandular regions of the stomach was recorded and which site the most severe ulcers were found. Results: The prevalence of EGUS severity score ≥2 was 53%. The most severe lesions were commonly observed at the margo plicatus. Although older horses were not more likely to be affected by clinically significant EGUS they were more likely to have lesions in both the glandular and nonglandular regions. Differences in location of EGUS lesions were identified in different age groups, breed types and in horses exposed to different levels of work. Conclusion and potential relevance: This study confirms that gastric ulceration can be prevalent in a group of apparently clinically normal horses, not in intensive work. Further investigation of reasons for differences in EGUS location between different populations may aid toward the development of novel preventive measures.     

Evaluation of heart rate and rhythm during exercise

Heart rate and rhythm can readily be monitored during exercise. Although there is considerable variation depending on the athletic discipline, exercise can be considered to be one of the most physiologically demanding times for the cardiovascular system. Assessment of heart rate during exercise typically provides information regarding fitness and the intensity of exercise, and on some occasions may provide an early indication of disease. Cardiac causes of poor performance occur relatively infrequently in comparison with disorders of the musculoskeletal and respiratory systems. Nevertheless, exercise induces cardiac hypertrophy, which predisposes athletes to valvular regurgitation and arrhythmias. Consequently cardiac murmurs and arrhythmias are frequently present in equine athletes, whereupon the clinical significance can be difficult to determine. Undertaking an exercise test to identify exercise‐induced arrhythmias is important in the assessment of poor athletic performance and the risk of sudden cardiac death during exercise. This paper describes the assessment of heart rate and rhythm during exercise. Most research has been undertaken on racehorses but, where data are available for other disciplines, they have been included. Considerations regarding the choice, type and design of exercise test were detailed in the first paper in this series.     

Risk factors associated with equine gastric ulceration syndrome (EGUS) in 201 horses in Denmark

Reasons for performing study: The prevalence (up to 93% in Thoroughbred racehorses) and severity of equine gastric ulceration syndrome (EGUS) has been associated with type of training and differing management practices. However, there have been few studies to confirm these findings in nonracehorses in Europe. Objectives: To investigate the prevalence of EGUS in a population of Danish horses, during winter when the horses had been housed and fed for at least 8 weeks and to analyse the influence of feed, work level and environment on the risk of EGUS of §grade 2 in severity. Methods: A total of 201 horses, not in active race‐training, were evaluated, representing 23 different stables from all 5 regions within Denmark. All horses were considered to be healthy and not on medical treatment for EGUS. Endoscopically observed ulcer lesion scores were based on the number present (0–4) and severity (0–5). Univariate and multivariable mixed effects logistic regression models were developed using EGUS score as the dependent variable. An ulceration severity score of §2 was regarded as being clinically significant. Separate models were developed for horses with ulcers in either the glandular or nonglandular regions of the stomach graded §2 (EGUS §2) and for those horses that had nonglandular ulcers graded §2 (NG §2). Results: In this population, 53% (107/201) of horses were graded as having EGUS §2 with 95 (47%) horses having NG §2. Three variables were significantly (P<0.05) associated with EGUS §2: straw being the only forage available; exceeding 2 g/kg bwt of starch intake/day or §1 g/kg bwt/meal; and water not being available in the turn out paddock. Risk of NG §2 significantly increased when straw was the only forage available, 1 g/kg bwt of starch/meal was exceeded, water was not available in the turnout paddock and the interval between forage feeding was <6 h. Conclusion and potential relevance: This study has confirmed that components of the diet, readily modifiable, may have an important impact on the risk of EGUS in the nonracehorse. Differences in the multivariable models produced for all ulcers and nonglandular ulcers support differences in the aetiology of ulcers in different locations of the stomach.     

Characteristic of Inflammatory Airway Disease in Japanese Thoroughbred Racehorses

Inflammatory airway disease (IAD) is a common cause of poor performance, interruption of training and premature retirement in racehorses. It is also reported that up to 80% of horses are affected at some point in the first years of training in UK and Australia. However, no studies with regard to the information on occurrence of IAD in Japanese Thoroughbred racehorses have been reported. To investigate the occurrence and the characteristics of IAD, epidemic research including endoscopic examination of the airway tract and trachea wash was conducted for Thoroughbred racehorses presenting coughs or poor performance which airway tract disease was suspected stalled in training facility managed by Japan Racing Association. Fifty-six out of 76 Thoroughbred racehorses (73.7%) presenting coughing or poor performance were diagnosed as IAD. Mean incidence rate of IAD was 0.3% and it has been confirmed that constant number of IAD exists in Japan. Up to 35.7% of IAD horses showed upper airway abnormalities in some extent. There was a trend for IAD horses to use wood shavings for bedding and fed hay from the ground compared with the control group. Therefore, improvement of stabling environment may aid in preventing IAD. This study demonstrated that Japanese Thoroughbred racehorses are affected by IAD likewise other countries as well as demonstrated the characteristics of IAD which may contribute to the clarification of the pathogenesis of IAD.     

Efficacy of a Combination of Apolectol,Live Yeast (Saccharomyces cerevisiae [CNCM I-1077]), and Magnesium Hydroxide in the Management of Equine Gastric Ulcer Syndrome in Thoroughbred Racehorses: A Blinded,Randomized, Placebo-Controlled Clinical Trial

To date, prevention of equine gastric ulcer syndrome (EGUS) has relied on management changes or pharmaceutical agents. The identification of an alternative means of prevention would be useful. Therefore, the objective of this study was to evaluate the combination of Apolectol, a live yeast (Saccharomyces cerevisiae [CNCM I-1077]), and magnesium hydroxide for the prevention of development of, or exacerbation of existing, EGUS in Thoroughbred racehorses. Twenty-four Thoroughbred racehorses without significant gastric ulceration (grade, ≤2 of 4) were identified on gastroscopy. Treated horses received 95 g Apolectol, 2 g S. cerevisiae, and 20 g magnesium hydroxide 1–4 hours before exercise. Control horses received 95 g of a feed pellet as a placebo. Gastroscopy was repeated at 24–27 days. There was no change in squamous (P = .45) or glandular (P = 1.0) ulcer grade over time in horses in the treatment group. In the placebo group, ulcer grade increased in both the squamous (P = .04) and glandular (P = .19) mucosa but only reached significance in the squamous mucosa group. Worsening of the ulcer grade was more likely in the placebo group in the glandular (P = .04) but not in squamous (P = .10) mucosa. The combination studied may be an effective prophylactic against EGUS development or exacerbation.     

The Contribution of Specific and Nonspecific Biomarkers in Diagnosis of Equine Gastric Ulcer Syndrome (EGUS) Under Field Condition

The aim of this study is to investigate the diagnostic efficiency of gastrin, pepsinogen, proinflammatory cytokines (TNF-α, IL-6), and oxidative stress biomarkers in horses with equine gastric ulcer syndrome (EGUS). Thirty horses diagnosed with gastroscopic EGUS and 15 clinically healthy horses were selected for this study. The serum levels of gastrin, pepsinogen showed nonsignificant changes in horses with EGUS when compared with healthy horses. The serum levels of TNF-α, IL-6 revealed a significant increase in horses with EGUS when compared with healthy ones. Oxidative stress is evident in horses with EGUS in comparison with healthy horses as detected by higher levels of malondialdehyde (MDA) and decreased serum levels of total antioxidant capacity (TAC), Superoxide dismutase (SOD), glutathione (GSH), and nitric oxide (NO). MDA and TNF-α showed better sensitivity and specificity than IL-6 in distinguishing horses with EGUS from control horses. Conclusively, examination of serum gastrin and pepsinogen levels had a limited value in diagnosis of EGUS in horses under investigation. Moreover, this study showed that oxidative stress is evident in horses with EGUS. Higher levels of TNF-α and IL-6 indicate their role in EGUS pathogenesis in horses. Finally, MDA, TNF-α, and IL-6 could be used as biological markers for preliminary screening of horses with EGUS. Gastroscopy still accredited as the “gold standard” for diagnosis EGUS.     

Scintigraphic identification of skeletal muscle damage in horses 24 hours after strenuous exercise

The uptake of the bone-seeking radiopharmaceutical 99mTc-MDP by damaged skeletal muscle in horses is evaluated. Twenty-four hours following strenuous exercise, 109 racehorses with a history of inadequate athletic performance and subtle lameness were imaged using scintigraphic techniques. Ten horses (9.2 per cent) demonstrated abnormal uptake of the radioisotope within skeletal muscles. A muscle biopsy from one of these horses confirmed that the muscles with increased scintigraphic activity had histologic evidence of rhabdomyolysis. This technique allows localisation and relative quantification of muscle damage and is a valuable aid in the evaluation of the athletic horse.     

Clinical evaluation of poor performance in the racehorse: the results of 275 evaluations

A clinical sports medicine evaluation was applied to 275 racehorses with a history of poor racing performance. The poor performance evaluation included a) general physical examination and basic laboratory screening; b) respiratory examination including auscultation, thoracic radiographs, ventilation-perfusion lung scintigraphy and upper airway endoscopy at rest and during maximal treadmill exercise c) examination of the musculoskeletal system including lameness examination, video gait analysis at high speed, post exercise serum chemistry to identify obvious as well as sub-clinical myopathies, high detail radiography and nuclear scintigraphy; d) cardiac examination including auscultation, electrocardiographic analysis during strenuous exercise and when indicated, echocardiography; and e) a standardised exercise stress test entailing the measurement of oxygen consumption, carbon dioxide production, venous blood lactate concentration and heart rate during sequentially increasing running speeds on the high speed treadmill. The choice of diagnostic methodologies utilised were tailored to each individual in order to determine most efficiently the abnormalities contributing to inadequate racing performance. The results of this clinical evaluation showed that 1) many of the diagnoses were subtle requiring the use of sophisticated diagnostic equipment including scintigraphy and dynamic evaluation of the horse exercising on the high speed treadmill and 2) 84 per cent of the horses were diagnosed as suffering from more than one problem leading to the supposition that inadequate athletic performance is often caused by a constellation of abnormalities requiring a comprehensive approach to diagnosing decreased athletic capability.     

Pathologic changes in the lumbosacral vertebrae and pelvis in Thoroughbred racehorses

OBJECTIVE: To describe the prevalence, characteristics, and severity of soft-tissue and osseous lesions in the caudal portion of the thoracic and lumbosacral vertebral column and pelvis in Thoroughbred racehorses. ANIMALS: 36 Thoroughbred racehorses that died or were euthanatized at California racetracks between October 1993 and July 1994. PROCEDURE: Lumbosacral and pelvic specimens were collected and visually examined for soft-tissue and osseous lesions. RESULTS: Acute sacroiliac joint injury was observed in 2 specimens. Signs of chronic laxity or subluxation of the sacroiliac joint were not observed in any specimens. Impingement of the dorsal spinous processes and transverse processes was observed in 92 and 97% of specimens, respectively. Thoracolumbar articular processes had variable degrees of degenerative change in 97% of specimens. Degenerative changes were observed at lumbar intertransverse joints and sacroiliac articulations in all specimens. Some degenerative changes were widespread and severe. CONCLUSIONS: Numerous degenerative changes affected vertebral processes, intervertebral articulations, and sacroiliac joints in these Thoroughbred racehorses. CLINICAL RELEVANCE: Various types of vertebral and pelvic lesions need to be considered during clinical evaluation of the back and pelvis in horses. Undiagnosed vertebral or pelvic lesions could be an important contributor to poor performance and lameness in athletic horses.     

Heart murmurs and valvular regurgitation in thoroughbred racehorses: epidemiology and associations with athletic performance

BACKGROUND: Cardiac murmurs associated with valvular regurgitation occur commonly in conditioned performance horses, but their association with athletic performance is unknown. HYPOTHESIS: Cardiac valvular regurgitation has a negative association with race performance. ANIMALS: Five hundred and twenty-six "race fit" Thoroughbred racehorses engaged in either flat (race distance 1,000-2,500 m) or jump racing (race distance 3,200-6,400 m). METHODS: Cardiac auscultation and color flow Doppler (CFD) echocardiography were performed on 777 occasions. The associations between the presence and severity of either an audible cardiac murmur or valvular regurgitation assessed by CFD, and published, objective measures of race performance were determined using a standard regression approach. RESULTS: The prevalence of murmurs and of regurgitation varied significantly between racetypes (P<.02), generally increasing from 2-year olds to chasers. There were no consistent associations between racing performance and either grade of murmur or regurgitation, whether the presence or absence of regurgitation or murmur, or only murmurs > or =3/6 or regurgitation > or =6/9, were considered. CONCLUSIONS AND CLINICAL IMPORTANCE: There were differences in prevalence and severity of murmurs of atrioventricular and aortic valve regurgitation between racehorses in different disciplines. Data also showed that neither regurgitation nor murmurs were negatively associated with Timeform rating, an index of UK racehorse quality, in any of the groups of racehorses studied.     

Prevalence of gastric ulcer syndrome in high-level endurance horses

Reasons for performing the study: Equine gastric ulcers syndrome (EGUS) prevalence studies are rare in the endurance horse and none has been carried out to date in horses competing at high level. Objectives: To determine the prevalence of EGUS in high‐level endurance horses. Methods: Thirty endurance horses competing at high level were selected and submitted to 2 gastroscopic examinations. The first gastroscopy was performed during the interseason period, and the second during the competition season within 2–3 days following a ride of 90–160 km. Data related to housing, feeding, training system as well as age, breed and gender were recorded for each horse. Results: The prevalence of squamous gastric ulcers was 48% during the interseason period (mean score 0.85 ± 0.13 on a scale from 0–4) and 93% during the competition season (mean score 1.60 ± 1.15) with a highly significant difference between the seasons (P = 0.001). Most of the lesions were situated in the squamous portion of the stomach but 33.3% of horses showed also glandular lesions. Significant influence of training and performance level on the gastric score (according to the distance of the ride preceding the second gastroscopy) was shown (P = 0.038). There was also a significant influence of housing on the gastric score (P = 0.002) showing higher scores in the horses kept totally on pasture (mean score: 2.14 ± 0.14) vs. horses housed in a mixed environment (stable + pasture, mean score: 1.43 ± 0.17). Both the pastured and (stabled + pastured) groups were receiving a grain supplement but the pastured group received a higher daily starch intake, which might explain the higher ulcer prevalence. There was no influence of age, breed or gender on the gastric scores. Conclusions: The high prevalence of gastric lesions observed in this study is probably related to the high level of training and performance of the horses examined compared to the population of horses included in the prior study. Potential relevance: This prevalence of EGUS in high‐level endurance horses is comparable to the prevalence established in racing horses. The equine veterinarians may take into consideration EGUS as a potential cause of poor performance.     

Arthroscopic removal of fractures of the lateral malleolus of the tibia in the tarsocrural joint: A retrospective study of 13 cases

There is limited information on the treatment of lateral malleolus (LM) fractures in the horse, with no previously published case series for the outcome following arthroscopic removal of such fractures. This report reviews and evaluates findings of a retrospective study of 13 horses admitted to a private equine referral hospital over a 10 year period (1999–2009) that underwent arthroscopic removal of fractures of the LM. Hospital records were reviewed and details including patient history, aetiology of the fracture and limb affected, results of all diagnostic tests and surgical reports were documented. Performance information concerning Thoroughbred horses that went onto race post operatively was collected using an online database. Owners and trainers were contacted regarding the return to performance for non‐Thoroughbred cases or those that did not go onto race post operatively. Of the 13 horses presented, 12 were Thoroughbreds, 9 of which were National Hunt racehorses and 3 were Flat racehorses. The other horse in the study was used for general purpose riding. All cases presented with an acute unilateral fracture. Eleven of the 13 had >6 months post operative follow‐up and all were nonlame. Of the 12 Thoroughbreds, 10 have raced again, a total of 104 times (median 5 times). The median time from surgery to return to racing was 241 days (180–366 days). It is concluded that horses with fractures of the LM have an excellent prognosis for return to full athletic performance following arthroscopic debridement; and that arthroscopic fragment removal is an appropriate treatment method for fractures of the LM.     

Equine gastric ulcer syndrome in adult horses: a review

In recent years, gastric ulceration has been recognised as a common, possibly performance-limiting disease of adult horses. Here, we aim to provide the reader with a useful review of recent literature covering all aspects of equine gastric ulcer syndrome (EGUS) in adult horses. The anatomy and physiology of the stomach, with particular reference to secretion of acid and mucosal protective mechanisms, are reviewed, as are the differing theories relating to the aetiopathogenesis of gastric ulceration. We also explore the possible influence of various management factors on development of the disease. The prevalence of the disease in racehorses has been reported to be as high as 100%. In general, horses that are in active training for racing tend to have a prevalence of around 90%, whereas pleasure horses in full work have a reported prevalence of approximately 60%. Emerging diagnostic tests which could obviate the need for gastroscopy are introduced and current recommendations for treatment are summarised, focussing on proton pump inhibitors, in particular omeprazole, administered orally. The oral administration of omeprazole has been shown to be effective in both treating horses with gastric ulceration and at preventing re-occurrence whilst the horses are in training, provided that daily dosing is maintained.     

Rethinking equine gastric ulcer syndrome: Part 1 – Terminology,clinical signs and diagnosis

Equine gastric ulcer syndrome (EGUS) is a common condition in the horse. A series of recent articles highlighting differences in healing of squamous and glandular ulceration have reinvigorated interest in the condition. The purpose of this series of articles is to review the current thinking on EGUS with particular emphasis on the differences between diseases of the squamous and glandular mucosae. This article, the first will review the terminology, clinical signs and diagnosis of EGUS in the horse.     

A scientific background for skeletal muscle conditioning in equine practice

The main goal of any conditioning programme in athletic horses is to improve performance by inducing physiological changes within the animal's body. Equine skeletal muscles have a considerable potential to adapt during training and these adaptations have important physiological implications that influence stamina, strength and speed. Although there is an extensive specialized literature in this regard, scientific based muscle conditioning methods have not been introduced sufficiently in the equine sport practice. After a brief synopsis of both equine muscle exercise physiology and muscular adaptations to training, including their physiological significance, this review focuses on specific training programmes that induce muscular adaptations in athletic horses. The article addresses the following principal question: what kind of stimuli for what kind of muscular adaptations? The experimental data are discussed separately for racehorses (thoroughbreds, trotters and endurance horses) and sport horses (dressage, show jumpers and carriage). Finally, published results about the influence of relevant training parameters (such as intensity, duration and type of exercise) on muscular responses are discussed, as well as those concerning overtraining and detraining. The article closes with some concluding remarks on importance of their application in practice.     

Treatment and prevention of equine gastric ulcer syndrome.

EGUS is a common problem in horses and foals. Acids are the important causative factors and current therapy targets the suppression of gastric HCl and creation of a permissive environment for ulcer healing. Diagnosis is based on history, clinical signs, gastroscopy, and response to treatment. Of the products available, only GastroGard (FDA approved) and ranitidine have been shown to be efficacious in the treatment of EGUS. Ranitidine is often associated with treatment failure as a result of incorrect dosing and lack of owner compliance, because of the three times daily dosing required. Also, EGUS occurs in critically ill neonatal foals, but the pathogenesis may be different than in adult horses and acid-suppressive therapy may not be as effective.     

Comparison of tracheal aspirates before and after high-speed treadmill exercise in racehorses

OBJECTIVE: To determine whether percentages of neutrophils in tracheal aspirate (TA) samples collected from racehorses are increased after exercise and whether interpretation of results from TA samples taken before and after exercise agree. DESIGN: Case series of 40 young Thoroughbred and Standardbred racehorses in race training presented for evaluation of poor performance. PROCEDURE: TA samples were collected endoscopically from racehorses presented for poor performance 24 h before and 1 to 2 h after high speed treadmill exercise testing. Aliquots of the retrieved fluid were cytocentrifuged and smears were stained with Diff-Quik. Mean neutrophil counts were expressed as percentages of the total number of inflammatory cells counted and subsequently were categorised as either above or below an accepted cut-off of 20%. Comparisons between percentages of neutrophils before and after exercise were made. RESULTS: Percentage of neutrophils from TA samples obtained from racehorses after exercise was significantly higher than neutrophil percentages from TA samples collected from the same horse before exercise. In horses with TA specimens that were categorised as having < or = 20% neutrophils before treadmill exercise, the percentage of neutrophils in their TA specimens after exercise was, on average, significantly higher and was greater than the cut-off value of 20%. CONCLUSION: Recent strenuous exercise may change the proportion of neutrophils in lower airways of racehorses and practitioners should be aware of this when collecting and interpreting the results from TA samples. The most practical time for collection of a TA sample to obtain the most diagnostically useful information might be after a suitable washout period of at least 1 to 2 h post-exercise.     

Changes over time in echocardiographic measurements in young Standardbred racehorses undergoing training and racing and association with racing performance

OBJECTIVE: To evaluate changes over time in echocardiographic measurements in young Standardbred racehorses undergoing training and racing and determine whether there was any relationship between cardiac dimensions and racing performance. DESIGN: Longitudinal observational study. ANIMALS: 103 horses. PROCEDURE: 2-dimensional and M-mode echocardiography was performed 4 times at 6-month intervals. RESULTS: Significant cardiac enlargement took place during the study period as indicated by increases in left ventricular internal diameter in diastole (LVIDd), estimated left ventricular muscle mass (LV mass), and mean wall thickness attributable to eccentric left ventricular hypertrophy. Estimated body weight was positively correlated with left ventricular size, and males had significantly larger LVIDd and LV mass than did females. Horses that were racing regularly had larger LVIDd and LV mass than did unraced horses. A significant relationship between left ventricular size and racing performance was observed. The relationship was strongest at the time of the fourth examination. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that age must be taken into account when interpreting results of echocardiography in young Standardbred racehorses because significant cardiac enlargement takes place with age and training. A larger heart was found in horses that were racing, and size of the heart was correlated with athletic performance of the horse.     

Retrospective trainer-reported incidence and predictors of health and training-related problems in standardbred racehorses

Information on the incidence of injury, illness, and unexplained loss of athletic performance of 2345 Standardbred racehorses was gathered from a telephone survey of 177 trainers during the 1996-1997 season. Trainer-reported incidence of infection and illness (18%) was higher than the incidence of musculoskeletal problems (10%) or unexplained athletic performance loss (6%). Older horses (>5 years) were more likely to develop musculoskeletal problems (odds ratio [OR] = 3.9; confidence interval [CI] = 1.8-8.2) and performance loss OR = 2.3, CI = 1.1-5.2) than 2-year-old horses. Horses were more likely to suffer musculoskeletal problems if fast-worked on tracks or surfaces with no banking compared with those fast-worked on tracks with banking similar to commercial racetracks OR = 4.6, CI = 2.0-9.9). Horses given no warm-up before high-intensity exercise were more likely to suffer a musculoskeletal problem than horses given a light warm-up of 1 to 9 minutes OR = 2.5, CI = 1.5-4.4). Horses trained for more than 164 min·wk⁻¹ were more likely to suffer musculoskeletal problems OR = 1.7, CI = 1.1-2.8) and athletic performance loss OR = 2.5, CI = 1.4-4.4) than horses trained for shorter periods. Horses given a moderate weekly exercise duration (132-148 min·wk⁻¹) had the lowest rates of infection and illness, but short (114-131 min·wk⁻¹) or very long (>164 min·wk⁻¹) weekly exercise duration increased the risk of horses suffering infection and illness OR = 1.6, CI = 1.1-2.2 and OR = 1.3, CI = 1.0-1.9, respectively). We conclude that Standardbred trainers could avoid many training and health problems by using well-banked tracks, providing a proper warm-up, and avoiding excessive training.

Introduction

Racehorses suffer from a variety of health and training problems that may result in poor performance. Musculoskeletal injury is a major problem in Thoroughbred racehorses, accounting for as much as 53% of the lost training and racing days.[1 and 2] Thoroughbreds that race too often, [2 and 3] have insufficient training before racing, [4] or perform too much high-speed work [5] have a greater risk of musculoskeletal problems. Performance may also be affected by respiratory infection, which is responsible for 12% of lost training or racing days. [1]Poor performance can also develop in an otherwise apparently healthy horse. Such unexplained loss of athletic performance may arise from undiagnosed health problems or from too much training.[6] Overtraining described as a state of prolonged fatigue caused by too much training or insufficient recovery [7] has been demonstrated in horses in both cross-sectional and longitudinal studies, [8 and 9] but the incidence of athletic performance loss because of overtraining in the population is unknown. Recently reported prospective studies that used the same group of horses has found that overtraining appeared to be difficult to induce in horses, [10, 11, 12 and 13] which may indicate that overtraining accounts for little of the loss in athletic performance suffered by Standardbred racehorses.It is thought that lameness is the most important cause of poor racing performance in Standardbreds[14]; however, the incidence of musculoskeletal problems causing lameness in Standardbreds is lacking. There is also little information on the incidence of respiratory disease or athletic performance loss in Standardbreds. The purpose of this study was to determine the trainer-reported incidence of these problems in Standardbred racehorses and to reveal any association with factors such as sex, age, ability, training, track surface, and track design.

Materials and methods

A survey was administered by telephone to 177 Standardbred racehorse trainers randomly selected from a list of 300 trainers compiled by Harness Racing New Zealand. The survey was administered at the end of the 1996-1997 racing season, which lasts from about September through June, and questions asked during the survey related to the 1996-1997 racing season. Trainers were asked to recall the total number of horses that experienced an unexplained and consistent loss of athletic performance (“performance decrease that lasted for at least two weeks, which was not obviously as a result of tying up, infection, illness, or musculoskeletal problems”). Trainers were also asked for the total number of horses that suffered infection or illness (viral and bacterial infections and respiratory diseases but not bleeding from the lungs), and musculoskeletal problems (lameness caused by muscle, tendon, bone, or back injuries that resulted in lost training days). Pilot work involved testing the questionnaire on 10 local horse trainers; from their feedback and that of other colleagues and horse trainers, more than 11 revisions were made. The interview consisted of 65 questions and lasted approximately 20 minutes. The incidences of performance loss and health problems detailed in this study are trainer-diagnosed; however, in the majority of cases (80%), the horses were also examined by a veterinarian and their diagnosis was consistent with the trainer's. Unfortunately, full details of the veterinary examination were not obtained during this study.To examine the influence of track design and banking, trainers were asked to compare the banking of their training tracks to the banking of a commercial racetrack (Forbury Park Raceway, Dunedin, New Zealand, which had a banking angle of approximately 2.3 degrees). Trainers had to decide whether the banking of their track was more, less, or about the same as the banking of the commercial track. Because of the need to keep the questionnaire to a reasonable size, in-depth training data was collected on only one particular group of horses—qualified maidens. Qualified maiden racehorses (previously raced but unplaced) represent the largest group of racehorses in training in New Zealand. Trainers were also asked whether they trained their other horses (faster, slower, unqualified, 1-7, or >7 wins) any differently from the qualified maidens. Information on training type, duration, and intensity were gathered for each day of a typical training week. Exercise duration and total training workload was divided into quintiles (5 equal sections) and contrasts between the quintiles were then examined. Trainers were specifically asked about the duration of the warm-up, which was not included in the total training time. Warm-up was defined as the initial preparatory phase of a training session in which the horse is slowly accustomed to low-intensity exercise and prepared for further high-intensity exercise.Although it is acknowledged that career wins is a crude method of assessing racing ability, it was the most appropriate method available to the researchers during a phone interview that gave some indication of horses' ability. Trainers were therefore asked about the number of wins for each horse and horses were grouped according to the total number of career wins. The Human Ethics Committee of the University of Otago reviewed and approved this project (reference number 97/049).The survey data were analyzed using a repeated-measures general modeling procedure (Proc Genmod, SAS Institute, Cary, NC), which estimated the effect of age, sex, gait, number of wins, warm-up, track design, training duration, and workload as odds ratios ORs). The OR is a way of comparing whether the probability of a certain event is the same for two groups. An OR of 1 implies that the event is equally likely in both groups, whereas an OR of more than one implies that the event is more likely in the first group compared with the second. For example, the odds of a horse suffering a musculoskeletal injury if fast-worked on tracks with no banking is 0.52 (cases/noncases = 12 injured/23 noninjured), whereas the odds of a horse suffering a musculoskeletal injury on well-banked tracks is 0.11 (37 injured/329 noninjured). Therefore, the OR is 4.6 and is interpreted as: 4.6 horses suffer a musculoskeletal injury if fast-worked on an unbanked track compared with every 1 horse that suffers the same injury when fast-worked on well-banked tracks. Proc Genmod (SAS Institute) analyzed the total number of horses in a particular subgroup and the total number of problems in the same subgroup for each trainer. A type I error of 5% was chosen for declaration of statistical significance; precision of estimates was represented by the 95% confidence interval (CI), the likely range of the true value.To estimate the reliability of the trainer's responses, a second questionnaire identical to the first was administered to 17 randomly selected trainers from the same sample 8 months after the original survey. The trainers' responses to the same questions from separate surveys given 8 months apart were used to gauge reliability of the survey. Questions on the sex, gait, and number of race wins of the horses under the trainers' care that suffered health and training-related problems were analyzed. These variables represented population characteristics of the horses that could change with time as horses entered or left the trainers stables, and therefore affect the reliability of the reported data. Survey reliability was found by comparing the empirical standard error of the odds ratio from the initial (Main) and second (Rely) surveys after adjustment for sample size. When the empirical standard error was similar (within one decimal place) between studies, then reliability was considered low, but when the empirical standard error was smaller in the Rely survey compared with the Main survey, then the reliability of the survey was acceptable.

Results

Overall training and health problems

Horses were 2.1 times more likely to suffer from infections and illness than from musculoskeletal problems (CI = 1.4-2.8, P < .001) and musculoskeletal problems were 1.7 times more likely to occur than athletic performance loss (CI = 1.2-2.3, P < .001). Horses that had no recognized problems raced 12 ± 6 times (mean ± SD) over the main racing season (September 1996-June 1997).

Athletic performance loss

Sixty-eight trainers reported that a total of 146 horses developed a decrease in athletic performance not readily associated with musculoskeletal injury, illness, or tying-up during the season (6% of the 2345 horses sampled). Most horses (78%) that suffered athletic performance loss required at least 6 weeks to recover to normal form; the remaining 22% recovered within 4 weeks. In general, the decrease in athletic performance occurred towards the middle and end of the racing season. The incidence of athletic performance loss in the various subgroups of horses is shown in Table 1, and the ORs and confidence limits for statistically significant differences in incidence within each subgroup are shown in Table 2.