A. F. Clarke

Risk of fatality and causes of death of Thoroughbred horses associated with racing in Victoria, Australia: 1989-2004

REASONS FOR PERFORMING STUDY Determining the risk of fatality of Thoroughbred horses while racing is essential to assess the impact of intervention measures designed to minimise such fatalities. OBJECTIVES To measure the risk of racehorse fatality in jump and flat starts on racecourses in Victoria, Australia, over a 15 year period and to determine proportional mortality rates for specific causes of death. METHODS All fatalities of Thoroughbred horses that occurred during or within 24 h of a race were identified from a database. The risk of a start resulting in a racehorse fatality in all races and within flat and jump races, proportional mortality rates, population attributable risk, population attributable fraction and risk ratios were calculated along with 95% confidence intervals. Poisson regression was also performed to estimate risk ratios. RESULTS There were 514 fatalities over the 15 year period; 316 in flat races and 198 in jump races. The risk of fatality was 0.44 per 1000 flat starts and 8.3 per 1000 jump starts (18.9 x greater). The risk of fatality on city tracks was 1.1 per 1000 starts whereas on country tracks it was 0.57 per 1000 starts. Of the 316 fatalities in flat races, 73.4% were due to limb injury, 2.5% to cranial or vertebral injury and 19.0% were sudden deaths. Of the 198 fatalities in jump races, 68.7% were due to limb injury, 16.2% to cranial or vertebral injury and 3.5% were sudden deaths. The risk of fatality in flat starts increased between 1989 and 2004 but the risk in jump starts remained unchanged over the 15 year period. CONCLUSIONS The risk of fatality in flat starts was lower in Victoria than North America and the UK but the risk in jump starts was greater. Catastrophic limb injury was the major reason for racehorse fatality in Victoria but there was a larger percentage of sudden deaths than has been reported overseas. The risk of fatality in jump starts remained constant over the study period despite jump racing reviews that recommended changes to hurdle and steeple races to improve safety. POTENTIAL RELEVANCE This study provides important benchmarks for the racing industry to monitor racetrack fatalities and evaluate intervention strategies.

Risk factors for Thoroughbred racehorse fatality in jump starts in Victoria, Australia (1989–2004)

REASONS FOR PERFORMING STUDY The risk of fatality is greater in jump than in flat racing in Victoria, Australia. This is the first study to identify risk factors specific to jump starts in Victoria. OBJECTIVE To identify risk factors for fatality of Thoroughbred racehorses in jump starts on all racecourses in Victoria, Australia between 1989 and 2004. METHODS Fatalities comprised all horses that died during or immediately after a jump (hurdle or steeplechase) race or official jump trial and all horses that were subjected to euthanasia within 24 h of an event in which an injury was sustained. The retrospective study involved 191 case starts and 2324 control starts. Univariable and multivariable backward stepwise logistic regression was used to identify risk factors for fatality at any one start. A multiple level model was used with racecourse included as a random effect. RESULTS In the final multivariable model, the duration of the racing career of the horse, the number of flat, hurdle and steeple starts accumulated in the 60 days prior to the case or control start, the number of flat and jump starts accumulated over the racing career, if the horse had had a start between 1 and 14 days prior to the case or control start, the type of jump race (hurdle or steeple), the calendar year of the start and the location of the racecourse were associated with fatality. CONCLUSIONS The findings highlight the need to investigate further the differences between hurdle and steeplechase events and the adverse effect of prolonged prior flat racing careers on the risk of fatality in jump starts. POTENTIAL RELEVANCE This is the first study to examine risk factors for fatality in jump starts in Victoria. The results should shape the development of interventions to reduce the risk in jump starts in the future.

Prevalence of pharyngeal and laryngeal abnormalities in Thoroughbreds racing in Australia, and their association with performance

REASONS FOR PERFORMING STUDY Little information is available regarding the prevalence of abnormalities of the upper airway and their association with performance in the general population of Thoroughbred racehorses. OBJECTIVES To describe the prevalence of selected abnormalities of the upper airway and their association with performance in Thoroughbred racehorses in Australia. HYPOTHESIS That abnormalities of the upper airway of Thoroughbred racehorses are associated with poor race performance. METHODS Rhinolaryngoscopy was performed after racing and presence and characteristics of abnormalities of the larynx and pharynx were recorded in a prospective cross-sectional study of Thoroughbred horses racing in Victoria, Australia. RESULTS Rhinolaryngoscopy was performed once on each of 744 horses over 35 months. Fifty abnormalities of the upper airway were detected in 47 horses (6.3%, 95% confidence interval [CI] 4.7-83%). Epiglottic entrapment was detected in 7 horses (0.9%, 95% CI 0.4-1.9%) and was significantly (P = 0.015) associated with superior performance. Grade 2 asymmetry (4 grade scale) of the left arytenoid cartilage was detected in 9 horses (1.2%, 95% CI 0.5-2.4%) and was also associated with superior performance (P<0.001). Ulceration or erosion of the mucosa of the axial surface of one or both arytenoids was detected in 18 horses (2.4%, 95% CI 13-3.8%) and was not associated with alterations in exercise performance (P = 0.31). CONCLUSIONS Epiglottic entrapment, Grade 2 laryngeal asymmetry and mucosal erosions detected in Thoroughbred racehorses were not associated with impaired performance; therefore, surgical correction and concern over laryngeal function in horses with Grade 2 asymmetry may not be necessary in individuals performing to expectation.

IDENTIFICATION AND PREVALENCE OF ERRORS AFFECTING THE QUALITY OF RADIOGRAPHS SUBMITTED TO AUSTRALIAN THOROUGHBRED YEARLING SALE REPOSITORIES

We aimed to identify common mistakes made when radiographing yearling sale horses. Radiographic examinations from repositories at eight yearling sales held in Australia in 2003 were assessed by one of four veterinary radiology specialists. Each radiographic examination consisted of a maximum of 34 radiographs. Each radiograph was assessed for errors associated with movement, exposure, positioning, labeling or marker placement, and processing, and categorized as either ideal, less than ideal or nondiagnostic. In addition, from the first 800 sets catalogued, 167 were selected randomly and read twice by the four radiologists for agreement analysis. A total of 81,297 radiographs were examined for errors affecting quality. Positioning errors were the most common reason for radiographs to be considered nondiagnostic (2432/81,297; 3%), with the flexed lateromedial (LM) metacarpophalangeal joint, LM metatarsophalangeal joint, and the dorsomedial palmarolateral (DMPaLO) carpal views being the most frequently involved. Overexposure (14,357/81,297; 17.7%) was the most common reason for radiographs being categorized as less than ideal with the LM stifle view the most represented. Agreement within and between radiologists for reporting errors in positioning of the flexed LM metacarpophalangeal joint, LM metatarsophalangeal joint, and DMPaLO carpal views varied from slight to almost perfect. The low repeatability within radiologists on some views suggests that before declaring a radiograph nondiagnostic it is worth considering rereading it at another time. Care should be taken in positioning of the flexed LM metacarpophalangeal, LM metatarsophalangeal, and DMPaLO carpus views to maximize radiograph quality.

Association between the purchase price of Thoroughbred yearlings and their performance during the 2- and 3-year-old racing seasons

OBJECTIVES Describe the association between the purchase price of Thoroughbred yearlings sold in Australia and racing performance as 2- and 3-year-olds. METHODS Race performance data of 2773 Thoroughbred yearlings sold at auction during 2003 were collected. Associations between purchase price and the probability of starting, the number of race starts and the prize money earned were examined. RESULTS In total, 2206 (79.6%) horses started a race. The mean number of race starts was six and the mean prize money earned was A

An assessment of intra- and interobserver agreement of reporting orthopaedic findings on presale radiographs of Thoroughbred yearlings.

24,420. A total of 1711 (61.5%) horses earned prize money, 402 (14.4%) earned more than their purchase price, 312 (11.2%) earned more than A

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

40,000, the estimated cost of training, and 142 (5.1%) earned A

Tracheobronchoscopic assessment of exercise-induced pulmonary hemorrhage in horses.

40,000 more than their purchase price. There was a positive association between purchase price category and the probability of starting, number of starts, earning prize money and earning greater than A

Sudden death in racing Thoroughbreds in Victoria, Australia.

40,000 (P < 0.001). Purchase price category was negatively associated with the probability of earning greater than the purchase price (P < 0.001). The proportion of horses earning greater than the purchase price plus

Risk of fatality and specific causes of death of racehorses on racecourses in Victoria, Australia

40,000 was significantly different (P = 0.03) among the five price categories. CONCLUSION Yearling purchase price was positively associated with all race performance outcomes measured and researchers examining the race performance of yearlings purchased at sales should consider including purchase price when modelling. The Thoroughbred yearling market in Australia behaves in a similar manner to the United States market; owners pay a premium to enter the sport of racing and an additional premium in the quest to own a champion.