Correlation of racing performance with radiographic changes in the proximal sesamoid bones of 487 Thoroughbred yearlings

REASONS FOR PERFORMING STUDY: Proximal sesamoiditis has been a common and confusing radiographic diagnosis in Thoroughbred yearling surveys. This study categorised the radiographic appearance of yearling proximal sesamoid bones and determined their effect on the number of races started and earning potential for racing at ages 2 and 3 years. HYPOTHESIS: Yearlings with moderate to severe proximal sesamoiditis have decreased performance at age 2 and 3 years. METHODS: Survey radiographs of 487 Thoroughbred yearlings were reviewed. Proximal sesamoid bones were examined and findings placed into 7 categories, 5 of which measured size, shape, and number of vascular canals, and 2 examined the radiographic shape of the sesamoid abaxial surface. Records of horses age 2 and 3 years were reviewed to obtain the number of races completed and money won in those races. RESULTS: Vascular canals with parallel sides < 2 mm in width in any number were normal. Yearlings with 1 or 2 abnormally conformed vascular canals (nonparallel sides and > 2 mm in width) had a decrease in number of race starts at age 2 years when compared to normal horses. This same change in the fore- or hindlimbs was associated with decreases in starts and earnings at age 2 years. If uniformly present in both fore- and hindlimbs there was no difference from normal horses. Yearlings with > 2 irregular vascular canals had a decrease in number of race starts and earnings at age 2 and 3 years. Changes in proximal sesamoid bone contour did not affect performance. CONCLUSIONS: Horses with enlarged vascular canals, within their sesamoids as yearlings, start fewer races and earn less prize money than horses with normal vascular canals. POTENTIAL RELEVANCE: One or two enlarged canals affected horses as 2-year-olds. Three or more enlarged vascular canals affected horses at ages 2 and 3 years, which should be taken into account when examining radiographs for potential purchase of young horses.     

Radiographic changes in Thoroughbred yearlings. Part 2: Associations with racing performance

REASONS FOR PERFORMING STUDY: Although the radiographic examination of yearlings has become commonplace at some large Thoroughbred sales, there are few data to support the decisions facing veterinarians who are asked to evaluate future racing potential. OBJECTIVES: To identify radiographic changes in the fetlocks, proximal sesamoid bones, carpi, tarsi, stifles and fore feet of Thoroughbred yearlings associated with future racing performance during ages 2 and 3 years. METHODS: Radiographs from routine pre- and post sale examinations of 1162 yearlings were used to identify individual radiographic changes in sale yearlings. Starting a race, the percent of starts placed, money earned and earnings per start were used to assess racing performanceand examined for associations with the radiographic changes observed. RESULTS: Overall 946 (81%) yearlings started at least one race during ages 2 or 3 years. Fourteen of 24 (58%) yearlings with moderate or extreme palmar supracondylar lysis of the third metacarpus, 8 of 14 (57%) of those with enthesophyte formation on the proximal sesamoid bones and 19 of 30 (63%) of those with dorsal medial intercarpal joint disease started a race. The odds of starting a race when age 2 or 3 years were 3 times lower for yearlings with these changes (P < 0.01) compared with yearlings that did not have these changes. Twenty-five of 36 (69%) yearlings with proximal dorsal fragmentation of the first phalanx in the hind fetlock started a race and these yearlings were also less likely (OR = 0.51, P = 0.07) to start a race. Yearlings with enthesophyte formation on hind proximal sesamoid bones placed in a smaller percentage of starts (16%, P = 0.01) earned less money (987 US dollars, P = 0.02) and had lower earnings per start (252 US dollars, P = 0.03) compared to starters without this change. CONCLUSIONS: Although many of the changes observed on radiographs of sale yearlings do not appear to influence future racing performance, some are associated with reduced performance. POTENTIAL RELEVANCE: The results of this study are best applied in parallel with the clinical impressions of veterinarians experienced in examining radiographs of sale yearlings. Some findings support those established in the literature as incidental findings and others suggest new areas for concern not previously reported as a problem in Thoroughbred sale yearlings.     

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

Endoscopic assessment of airway function as a predictor of racing performance in Thoroughbred yearlings: 427 cases (1997-2000)

OBJECTIVE: To compare endoscopic findings of the upper portion of the respiratory tract in Thoroughbred yearlings with their subsequent race records to determine whether subjective assessment of airway function may be used as a predictor of future racing performance. DESIGN: Retrospective study. ANIMALS: 427 Thoroughbred yearlings. PROCEDURES: Endoscopic examination findings were obtained from the medical records and the videoendoscopic repository of the Keeneland 1996 September yearling sales. Racing records were requested for the yearlings through the end of their 4-year-old racing season (1997-2000). Twenty-nine measures of racing performance were correlated with endoscopic findings. Subjective arytenoid cartilage movement grades were determined, using a 4-point grading scale (grade 1 = symmetrical synchronous abduction of the arytenoid cartilages; grade 4 = no substantial movement of the left arytenoid cartilage). RESULTS: Of the 427 Thoroughbred yearlings included in this study, 364 established race records, and 63 did not. Opinions regarding suitability for purchase, meeting conditions of the sale, and the presence of epiglottic abnormalities had no significant association with racing performance. Arytenoid cartilage movement grades were significantly associated with many of the dependent variables. However, palatine abnormalities were not predictive of inferior racing performance. CONCLUSIONS AND CLINICAL RELEVANCE: Thoroughbred yearlings with grade-1 and -2 arytenoid cartilage movements had significantly better racing performance as adults, compared with yearlings with grade-3 arytenoid cartilage movements. In contrast, epiglottic and palatine abnormalities were not predictive of inferior racing performance. Therefore, evaluation of laryngeal function, but not epiglottic or palatine abnormalities, using the 4-point grading system, should be the major factor in developing recommendations for prospective buyers.     

Sudden death in racing Thoroughbred horses: an international multicentre study of post mortem findings

Reasons for performing study: To improve the understanding of exercise related sudden death in Thoroughbred racehorses. Objectives: To describe the post mortem findings in cases of sudden death associated with exercise in 268 Thoroughbred racehorses. Methods: Gross and histological post mortem findings of 268 cases of sudden death were collated and reviewed. Cases originated from 6 racing jurisdictions around the world. Sudden death was defined as acute collapse and death in a closely observed and previously apparently healthy Thoroughbred racehorse, during, or within one hour after, exercise. Cause of death as determined by the attending pathologist was categorised as definitive, presumptive or unexplained and compared between the different populations. Cardiopulmonary lesions recorded at post mortem examination were compared between different populations. Results: Pathologists recorded a definitive cause of death in 53% (143/268) of cases. Major definitive causes of sudden death included cardiac failure, apparent pulmonary failure, pulmonary haemorrhage, haemorrhage associated with pelvic fractures or with idiopathic blood vessel rupture, and spinal cord injury. A presumptive cause of death was made in 25% (67/268) of cases and death remained unexplained in 22% (58/268) of cases. There were several statistically significant inter‐population differences in the cause of death and in reporting of cardiopulmonary lesions. Conclusions: Sudden death can be attributed to a variety of causes. Causes of sudden death and the lesions found in cases of exercise‐related sudden death are similar in different racing jurisdictions. However, the lesions are often not specific for the cause of death and determination of the cause of death is therefore affected by interpretation by the individual pathologist.     

Ophthalmic examination findings of Thoroughbred racehorses in Australia

OBJECTIVE: To record the prevalence and document the types of eye disease in population of Thoroughbred racehorses in Victoria, Australia. DESIGN: Prospective study. ANIMALS: Two hundred four Thoroughbred racehorses. PROCEDURE: All horses and both eyes were examined at four metropolitan and two country racing stable complexes. Ophthalmic exam was performed following dark adaptation with a transilluminator, biomicroscope, and direct ophthalmoscope. Intraocular pressures were measured when indicated. Both pupils were dilated with tropicamide when indicated. RESULTS: One hundred eighty-two (89.2%) flat-racing and 22 (10.8%) jump-racing (hurdle or steeple) horses were examined. Age range: 2-9 years (mean 3.7 years, median 3); 97 (47.5%) male-neuter, 74 (36. 3%) female, 33 (16.2%) male. Potential vision-threatening eye disease was present in 15 (7.4%) different horses: complete lenticular cataracts 3, posterior lens luxation and cataract 1, large peripapillary 'butterfly' inactive lesions 3, large peripapillary 'butterfly' active lesions 2, peripapillary focal inactive 'bullet hole' chorioretinal lesions (> 20) 5, optic nerve atrophy 1. Non-vision threatening eye disease was present in 117 (57.4%) different horses, involving one or more ocular structures: lower eyelid scars 3; periocular fibropapillomatous disease 1; third eyelid squamous cell carcinoma 1; corneal scars 6; corneal band opacity 2; anterior iris synechia 1; developmental cataracts 36 (17.2%); peripapillary focal inactive 'bullet hole' chorioretinal lesions (< 20) 103 (50.0%); linear peripapillary hyperpigmentation bands 16 (7.9%). Unusual variations of normal ocular anatomy and colobomata was recorded in 11 (5.4%) different horses: granular iridica hypoplasia 3, granular iridica hyperplasia 2, multilobular granular iridica cyst 1, microcornea 1, hyaloid remnant 1, rotated optic nerve head 1, coloboma of the lens 1, atypical coloboma of the retina 1. CONCLUSIONS: This survey demonstrates that the prevalence of vision-threatening eye disease in racing horses may be greater than previously perceived, and highlights the importance of ocular examination within any routine physical examination of horses.     

Association of owner-reported noise with findings during dynamic respiratory endoscopy in Thoroughbred racehorses

Reasons for performing study: To determine the association between owner‐reported noise and findings during dynamic respiratory endoscopy (DRE) in a large case series. Hypothesis: The sensitivity of owner‐reported noise for dynamic upper respiratory tract obstructions in horses is low, and the specificity is high. Methods: One hundred horses underwent DRE for the investigation of abnormal respiratory noise and/or poor performance. The association of abnormal noise with findings during DRE was evaluated. Results: Eighty‐five horses underwent DRE for the investigation of abnormal respiratory noise. Of these, 82% were found to have one or more obstructive upper respiratory tract abnormalities during DRE. Forty‐eight percent of horses reported to gurgle, rattle or make a rough noise were diagnosed with solitary palatal dysfunction. A further 24% with this history showed palatal dysfunction in combination with an additional abnormality. Twenty‐seven percent of horses with a history of whistling or roaring showed some degree of recurrent laryngeal neuropathy. Seven percent of horses with a history of whistling or roaring had vocal cord collapse as a solitary condition, whereas 40% had vocal cord collapse and another abnormality. The sensitivity of abnormal respiratory noise for any obstruction of the upper portion of the respiratory tract was high (84%), while the specificity was low (25%). Characteristic owner reported noise patterns showed moderate to low sensitivity for specific conditions. Whistling and roaring showed the highest specificity (≥80%) for laryngeal dysfunction. Conclusion: Diagnosis of upper respiratory tract obstructions based solely on owner‐reported noise and performance history may result in incomplete diagnoses. Clinical relevance: DRE should be performed in horses with abnormal respiratory noise to rule out complex conditions of the upper portion of the respiratory tract.     

Association between findings on palmarodorsal radiographic images and detection of a fracture in the proximal sesamoid bones of forelimbs obtained from cadavers of racing Thoroughbreds

OBJECTIVE: To determine the distribution for limbs and bones in horses with fractures of the proximal sesamoid bones and relationships with findings on palmarodorsal radiographic images. SAMPLE POPULATION: Proximal sesamoid bones obtained from both forelimbs of cadavers of 328 racing Thoroughbreds. PROCEDURE: Osteophytes; large vascular channels; and fracture location, orientation, configuration, and margin distinctness were categorized by use of high-detail contact palmarodorsal radiographs. Distributions of findings were determined. Relationships between radiographic findings and fracture characteristics were examined by use of chi2 and logistic regression techniques. RESULTS: Fractures were detected in 136 (41.5%) horses. Biaxial fractures were evident in 109 (80%) horses with a fracture. Osteophytes and large vascular channels were evident in 266 (81%) and 325 (99%) horses, respectively. Medial bones typically had complete transverse or split transverse simple fractures, indistinct fracture margins, > 1 vascular channel that was > 1 mm in width, and osteophytes in abaxial wing and basilar middle or basilar abaxial locations. Lateral bones typically had an oblique fracture and distinct fracture margins. Odds of proximal sesamoid bone fracture were approximately 2 to 5 times higher in bones without radiographic evidence of osteophytes or large vascular channels, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Biaxial fractures of proximal sesamoid bones were common in cadavers of racing Thoroughbreds. Differences between medial and lateral bones for characteristics associated with fracture may relate to differences in fracture pathogeneses for these bones. Osteophytes and vascular channels were common findings; however, fractures were less likely to occur in bones with these features.     

Comparison of bronchoalveolar lavage findings and measurements of gas exchange during exercise in horses with poor racing performance

Twenty-four Thoroughbred and twelve Standardbred racehorses aged between 2 and 6 years, presented for reported poor racing performance, underwent clinical exercise testing. During the last 10 s of exercise at each speed throughout an incremental speed exercise test on a treadmill inclined at a 10% slope, samples of arterial blood and expired gases were collected. Maximum oxygen uptake and the partial pressures of oxygen and carbon dioxide in arterial blood were determined. These values were compared between the two breeds of horses and also with reference to cytological findings of bronchoalveolar lavage samples, including neutrophil, erythrocyte and haemosiderophage percentage and the total nucleated cell concentration. The results revealed an inverse relationship (Spearman R = -0.45, p<0.05) between the total nucleated cell count in bronchoalveolar lavage samples and arterial oxygen partial pressure during exercise at 11 m.s^-1. This result suggests that subclinical pulmonary disease may be a more important cause of poor racing performance than previously thought. Also of note was a positive correlation (Spearman R = 0.50, p<0.05) between maximum oxygen untake and the percentage of erythrocytes.     

Comparison of bronchoalveolar lavage findings and measurements of gas exchange during exercise in horses with poor racing performance

Twenty-four Thoroughbred and twelve Standardbred racehorses aged between 2 and 6 years, presented for reported poor racing performance, underwent clinical exercise testing. During the last 10 s of exercise at each speed throughout an incremental speed exercise test on a treadmill inclined at a 10% slope, samples of arterial blood and expired gases were collected. Maximum oxygen uptake and the partial pressures of oxygen and carbon dioxide in arterial blood were determined. These values were compared between the two breeds of horses and also with reference to cytological findings of bronchoalveolar lavage samples, including neutrophil, erythrocyte and haemosiderophage percentage and the total nucleated cell concentration. The results revealed an inverse relationship (Spearman R = -0.45, p < 0.05) between the total nucleated cell count in bronchoalveolar lavage samples and arterial oxygen partial pressure during exercise at 11 m.s(-1). This result suggests that subclinical pulmonary disease may be a more important cause of poor racing performance than previously thought. Also of note was a positive correlation (Spearman R = 0.50, p < 0.05) between maximum oxygen uptake and the percentage of erythrocytes.     

Retrospective study on the effect of wither fracture on racing performance in Thoroughbred racehorses in Hong Kong (2003 to 2013)

The training programme for Thoroughbred flat racehorses is intense, with pressure to limit nontraining days. Fracture of the dorsal spinous processes is a traumatic event that affects a horse's ability to train and race, with little information available regarding short‐term treatment and long‐term outcomes for elite racing horses. Using a retrospective cohort study of the Hong Kong Jockey Club's veterinary clinical records, cases of wither fracture were identified radiographically, with clinical features, treatment and subsequent return to training and racing described. The prevalence of wither fracture was 0.152% and in 6 out of 8 cases, the fracture occurred following identified trauma. Clinical signs varied from mild swelling and pain of the affected region to acute, severe forelimb lameness with spinal deformation. Prognosis for recovery was excellent, with all horses returning to a level of racing performance equal to or better than before the injury. The time from injury to return to ridden work was <2.5 months and return to racing was 9 months, with horses that returned to training sooner after injury having more favourable outcomes. The period of rest identified in this study was shorter than previously reported, with the median interval between injury and first gallop <2.5 months and most horses back racing within 6 months.