Local airborne particulate concentration is associated with visible tracheal mucus in Thoroughbred racehorses

Reason for performing study: Accumulations of tracheal mucus assessed by endoscopic examination are associated with poor performance in racehorses. The air quality in horses' stalls may contribute to this visible tracheal mucus. Objectives: To determine whether the concentration and number of airborne particulates in stalls are associated with visible accumulations of tracheal mucus and with the number of inflammatory cells in tracheal aspirates. Methods: We studied 107 racehorses from 3 stables, in 3 different months, and measured airborne particulate matter 3 times daily in each of the stalls. On each monthly visit, horse airways were examined endoscopically and assigned a mucus score, and tracheal lavage was performed. Bivariate procedures, general estimating equations and linear mixed models were applied to estimate the association between PM and the presence of accumulations of mucus and number of inflammatory cells. Results: Stable, stall, month and PM were all significantly associated with the presence of accumulations of tracheal mucus, which had an overall prevalence of 67%. The odds of horses having visible accumulation of mucus were increased when horses occupied enclosed stables or stalls with higher particulate concentrations, and when concentrations of larger particles (≤10 µm in diameter) were elevated. Sixty‐eight percent of tracheal wash samples contained more than 20% neutrophils. Increased numbers of neutrophils were associated with the concentration of smaller particles (≤2.5 µm in diameter). Potential relevance: Careful consideration of stable construction and management practices focused on maintaining the lowest possible dust concentrations throughout the day should reduce the prevalence of visible accumulations of tracheal mucus, potentially improving racing performance.     

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

OBJECTIVE: To determine the frequency of epistaxis during or after racing among racehorses and identify factors associated with development of epistaxis. DESIGN: Retrospective study. SAMPLE POPULATION: 247,564 Thoroughbred and 4,045 Anglo-Arab race starts. PROCEDURE: Race start information (breed, age, sex, racing distance, and race type) was obtained for Thoroughbred and Anglo-Arab horses racing in Japan Racing Association-sanctioned races between 1992 and 1997. All horses that raced were examined by a veterinarian within 30 minutes of the conclusion of the race; any horse that had blood at the nostrils was examined with an endoscope. If blood was observed in the trachea, epistaxis related to exercise-induced pulmonary hemorrhage (EIPH) was diagnosed. RESULTS: Epistaxis related to EIPH was identified following 369 race starts (0.15%). Frequency of EIPH-related epistaxis was significantly associated with race type, age, distance, and sex. Epistaxis was more common following steeplechase races than following flat races, in older horses than in horses that were 2 years old, following races < or =1,600 m long than following races between 1,601 and 2,000 m long, and in females than in sexually intact males. For horses that had an episode of epistaxis, the recurrence rate was 4.64%. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that frequency of EIPH-related epistaxis in racehorses is associated with the horse's age and sex, the type of race, and the distance raced. The higher frequency in shorter races suggests that higher intensity exercise of shorter duration may increase the probability of EIPH.     

Long-term study of partial arytenoidectomy with primary mucosal closure in 76 Thoroughbred racehorses (1992-2006)

REASON FOR PERFORMING STUDY: The effectiveness and best method to perform a partial arytenoidectomy in racehorses is unclear. This study was performed to evaluate the success of and complications that can occur after a unilateral partial arytenoidectomy with primary mucosal closure in Thoroughbred racehorses. HYPOTHESIS: Partial arytenoidectomy is an effective surgical procedure to return Thoroughbred racehorses, afflicted by arytenoid chondropathy or a failed laryngoplasty, to preoperative levels of performance. METHODS: Seventy-six Thoroughbred racehorses admitted to the New Bolton Centre between 1992 and 2006 were assessed. Information was obtained from the medical records about the horse, laryngeal abnormalities, surgery and other findings during hospitalisation. Racing information was evaluated relative to those independent variables by an analysis of variance with a level of significance of P<0.05. RESULTS: Arytenoid chondropathy was the presenting complaint in 54 horses and failed laryngoplasty in 22 horses. Thirteen horses (17%) underwent a second surgery for laser excision of intralaryngeal granulation tissue at the arytenoidectomy site. Seventy-three horses were discharged from the hospital and racing outcome was evaluated. Sixty horses (82%) raced after surgery and 46 horses (63%) raced 5 or more times after surgery. The median time from surgery to the first start was 6 months. The average earnings/start was not significantly different before and after surgery. There was no association between earnings after surgery and age, gender, location of lesion, type of lesion, duration of tracheal intubation or undergoing a second surgery. CONCLUSIONS AND POTENTIAL RELEVANCE: A Thoroughbred racehorse is likely to race after a unilateral partial arytenoidectomy with primary mucosal closure and return to a preoperative level of performance.     

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.     

Effect of an external nasal dilator strip on cytologic characteristics of bronchoalveolar lavage fluid in Thoroughbred racehorses

OBJECTIVE: To determine the effects of an external nasal dilator strip on cytologic characteristics of bronchoalveolar lavage (BAL) fluid in racing Thoroughbreds. DESIGN: Clinical trial. ANIMALS: 23 Thoroughbred racehorses in active training. PROCEDURE: Each horse raced on 2 occasions: once while wearing an external nasal dilator strip and once while not. Bronchoalveolar lavage was performed 12 to 18 hours after each race, and BAL fluid was analyzed for RBC and leukocyte counts and hemosiderin content. RESULTS: Mean +/- SEM count of RBCs in BAL fluid when horses raced without the nasal dilator strip (84.6 +/- 275 cells/microL) was not significantly different from count when they raced with it (41.7 +/- 12.2 cells/microL). Horses were grouped as having mild or severe bleeding on the basis of RBC count in BAL fluid after horses raced without the nasal dilator strip. Mean count when horses with severe bleeding raced without the nasal dilator strip (271.0 +/- 63.7 cells/microL) was significantly higher than mean count when these horses raced with the strip (93.8 +/- 376 cells/microL). Mean count of lymphocytes in BAL fluid was significantly lower after horses raced with the external nasal dilator strip. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that use of an external nasal dilator strip in Thoroughbred racehorses may decrease pulmonary bleeding, particularly in horses with severe exercise-induced pulmonary hemorrhage.     

Performance after partial arytenoidectomy without mucosal closure in 27 Thoroughbred racehorses

OBJECTIVE: To examine the effect of partial arytenoidectomy without mucosal closure on postoperative racing performance and long-term complications in Thoroughbred racehorses treated for laryngeal hemiplegia, arytenoid chondropathy, or failed laryngoplasty. STUDY DESIGN: Retrospective study. ANIMALS: Twenty-seven Thoroughbred racehorses. METHODS: Medical records of Thoroughbred racehorses that had partial arytenoidectomy without mucosal closure between 1992 and 2002 were reviewed. Horses were divided into groups: horses that had not raced (Group 1) and those that had raced (Group 2) before surgery. Lifetime race records were compared between groups. A standard starts index (SSI) and performance index (PI) were used for Groups 1 and 2, respectively, to objectively evaluate each horse's postoperative performance. Telephone interviews of owners and trainers were used for subjective performance evaluation and to determine prevalence of long-term complications. RESULTS: Eleven (61%) Group 1 and 7 (78%) Group 2 horses raced and earned money after surgery. All Group 1 horses that raced performed at a level lower than the national average. Only 1 Group 2 horse had an improved PI score postoperatively. CONCLUSIONS: Thoroughbred racehorses have a fair prognosis for racing successfully after partial arytenoidectomy without mucosal closure. CLINICAL RELEVANCE: This technique may be a practical alternative to primary mucosal closure, would decrease surgical time, and avoid some problems reported with primary mucosal closure.     

Prevalence, heritability and significance of musculoskeletal conformational traits in Thoroughbred yearlings

REASONS FOR PERFORMING STUDY: The assessment of belief that equine conformation is associated with performance and durability is a fundamental concept of horsemanship. Surprisingly, there is almost no quantitative evidence to support these beliefs. OBJECTIVES: To assess the prevalence and heritability of conformational traits in Thoroughbred yearlings, and investigate their significance for subsequent turf flat-racing performance and durability. METHODS: Nine selected conformational traits were assessed in a consistent, qualitative manner by a single veterinary observer and entered into a database together with details of pedigree and racing records. RESULTS: Conformational data were collected from 3916 Thoroughbred yearlings sold at public auction during the 7 year period 1993-1999. Most of the horses (72%) raced in the UK in turf flat races; just 7% of the yearlings failed to race. Prevalence of conformational defects for the UK horses was reported, with turned out feet the most commonly recorded defect (30% of all horses). There was a tendency towards a greater proportion of horses with defects in the group of unraced horses compared with horses that raced, but this was not statistically significant. There were some significant associations between racing performance and conformational defects but these were found to be almost completely explained by an effect of sire. All of the conformational traits showed considerable evidence of genetic influence, with heritability indices ranging 0.16-1.00. CONCLUSIONS AND POTENTIAL RELEVANCE: Overall, there were only weak associations between performance and conformation that could not be accounted for by the very strong relationship between pedigree and conformation. Further study of potential association between highly heritable conformation traits and racing durability and racing performance should be undertaken utilising validated, quantitative methods and technology.     

The association of 2‐year‐old training milestones with career length and racing success in a sample of Thoroughbred horses in New Zealand

Reasons for performing study: There is increasing evidence that exercise early in life has a positive effect on musculoskeletal health. At present, there is little whole population research investigating the effect of racing as 2‐year‐olds on future racing career. Objectives: To investigate the association between attaining training milestones as 2‐year‐olds with length of career and racing success in Thoroughbred horses in New Zealand. Methods: Retrospective data were obtained of the 2001/02‐born Thoroughbred foal crop. The 3 training milestones were: registered with a trainer, trialled and raced. The association of the training milestones with career length was measured using the outcomes: number of race starts and number of years raced, in a Cox regression model. Logistic regression models analysed the association of the training milestones with the outcomes: won or placed in a race. Linear regression was performed to assess the association of training milestones with total career earnings. Results: Of 4683 horses in the population; 3152 horses were registered with a trainer, 2661 horses trialled and 2109 horses raced. Horses that raced as 2‐year‐olds had significantly (P<0.001) more race starts than those first raced as 3‐year‐olds or older, this was also true when the 2‐year‐old year data were omitted. Horses that raced as 2‐year‐olds had significantly (P<0.001) more years racing. Horses registered with a trainer, trialled or raced as 2‐year‐olds were more likely to have won or been placed in a race than those that achieved the milestones as 3‐year‐olds or older. Horses that first trialled and raced as 2‐year‐olds had greater total earnings than those that first trialled or raced at a later age. Conclusions and potential relevance: Two‐year‐old training milestones had a strong association with positive racing career outcomes. Horses in training or racing as 2‐year‐olds may have better musculoskeletal health throughout life than horses that are first in training or racing at a later age.     

Tracheal Endoscopic and Cytological Findings and Blood Examination Results in Thoroughbred Racehorses Suspected to have Lower Respiratory Tract Disease

Cytology of tracheal aspirates, tracheal endoscopic and blood tests were carried out to 86 Thoroughbred racehorses presenting coughs or poor performance which were suspected to have lower respiratory tract disease (LRTD) to assess the conditions of the disorders. Racehorses were classified into coughing (66 horses) and non-coughing (20 horses) groups based on clinical symptoms. Nine Thoroughbred racehorses without respiratory abnormality were used as controls. Assessment of grades of airway mucus, cytology of tracheal aspirates and serum amyloid A (SAA), fibrinogen (Fbg) and pulmonary surfactant protein D (SP-D) measurements were performed. Relationships between age, gender and racing careers were also investigated to understand the characteristics of LRTD in racehorses. Mean age was significantly higher in non-coughing group compared to coughing group. Existence of racing career and number of starts were significantly greater in non-coughing group compared to coughing group. On the other hand, grades of airway mucus were significantly higher in coughing group compared to control group. Percentages of neutrophils in tracheal aspirates were significantly higher in coughing group compared to non-coughing and control groups. SAA, Fbg and SP-D were higher in coughing group compared to non-coughing and control groups indicating that condition of coughing group is in the acute phase. Positive rate of inflammatory airway disease was significantly higher in coughing and non-coughing groups compared to control group. It was concluded that carrying out comprehensive evaluation including investigation on SAA, Fbg and SP-D analysis with airway assessment to Thoroughbred racehorses which were suspected to have LRTD are useful procedure to understand the pathological condition which aid to initiate appropriate treatment, prognosis judgment or to advise trainers to consider altering training regimen.     

Cytologic findings of tracheobronchial aspirates from 66 thoroughbred racehorses.

Tracheobronchial aspirates obtained from 66 healthy Thoroughbred racehorses in training at the same track were examined. Twenty-seven percent of the horses had greater than 20% neutrophils in the aspirate. Eosinophils, mast cells, giant cells, and Curschmann's spirals of mucus were observed in 94, 83, 65, and 42% of the horses, respectively. Hemosiderophages were observed in 86% of the horses, half of which had previous confirmation of exercise-induced pulmonary hemorrhage. Although fungal elements were seen in 70% of the horses, bacteria were detected in only 3% of the horses. The authors conclude that inflammatory airway disease is widespread in the racing Thoroughbred population.     

Pulmonary haemorrhage in standardbred horses after racing

SUMMARY Endoscopic examinations of the upper respiratory tract were done on 92 of 314 Standardbred horses that raced one or more times at 4 consecutive, weekly race meetings. Although participation was voluntary, the characteristics of the population of horses examined were not statistically different from those of all horses that raced. No horse showed epistaxis, but 34 (32.4%) examinations of the trachea revealed blood that ranged from a trace in the tracheal mucus to large amounts scattered over the tracheal walls. Forty-four horses exhibited minor degrees of pharyngeal lymphoid hyperplasia, 2 had asynchronous movement of the left arytenoid cartilage and 15 had grains of sand in the respiratory tract. There was no association between bleeding and age, sex, distance of race, place in race or date of race. Mucus and mucopurulent material occurred less often after longer races and more often on the last 3 race nights.     

Sternothyroideus myotomy, staphylectomy, and oral caudal soft palate photothermoplasty for treatment of dorsal displacement of the soft palate in 102 thoroughbred racehorses

Objective— To compare racing performance before and after sternothyroideus myotomy, staphylectomy, and oral caudal soft palate photothermoplasty in Thoroughbred racehorses with intermittent dorsal displacement of the soft palate (DDSP).
Study Design— Retrospective study.
Animals— Thoroughbred racehorses (n=102) with DDSP.
Methods— Retrieved data included signalment, primary complaint, and upper respiratory tract endoscopic finding. Lifetime race records were compared for earnings per start before and after surgery, days to 1st start, and races won postoperatively.
Results— Comparing mean earnings per start for 3 races before ($2792) and after ($3806) surgery, racing performance improved significantly after surgery in 63% (46/73) of horses that competed in at least 1 race before and after surgery ( P =.02). Mean and median days to 1st start after surgery were 109 and 69 days, respectively. Of horses that raced postoperatively 65% (60/92) won at least 1 race, and 77% (71/92) raced in >5 races after surgery.
Conclusions— Sternothyroideus myotomy, staphylectomy, and oral caudal soft palate photothermoplasty significantly improved racing performance in experienced Thoroughbred racehorses with performance limiting DDSP, and overall had a similar outcome to other reported surgical techniques for treatment of DDSP.
Clinical Relevance— Sternothyroideus myotomy, staphylectomy, and oral caudal soft palate photothermoplasty should be considered as a surgical approach to correction of DDSP in Thoroughbred racehorses; however, it is possible that staphylectomy may not be necessary to achieve a desirable outcome.     

Coughing in thoroughbred racehorses: risk factors and tracheal endoscopic and cytological findings

A matched case-control study was made of 100 thoroughbred horses which were coughing and 148 control horses which were free of clinical signs of respiratory tract disease. The variables identified by multivariable conditional logistic regression as being significantly associated with coughing included age (the risk decreased with age), the stage of training (horses in early training were at greatest risk), the time since the last race (horses that had never raced were at greatest risk) and the time since they were last transported (horses transported more than 14 days previously were more likely to cough than those transported within the last week). The coughing horses were significantly more likely to have high scores for upper and lower tracheal mucus and pharyngeal lymphoid hyperplasia. In addition, the tracheal aspirates of the coughing horses had increased odds of neutrophilia and were more likely to have intracellular bacteria than the control horses. However, a considerable proportion of the control horses had cytological and/or endoscopic evidence of airway inflammation.     

Racing performance after arthroscopic removal of apical sesamoid fracture fragments in Thoroughbred horses age > or = 2 years: 84 cases (1989-2002)

REASONS FOR PERFORMING STUDY: Studies have shown that surgical removal of apical fracture fragments in Standardbred racehorses carries the best prognosis for return to racing performance, but there are no reports involving mature Thoroughbred (TB) racehorses. OBJECTIVES: To describe the incidence of apical proximal sesamoid fractures in TB racehorses and determine probability and quality of racing performance after arthroscopic removal of such fractures in TB racehorses age > or = 2 years. METHODS: Medical records and pre- and post operative race records of TB racehorses age > or = 2 years that underwent arthroscopic surgery for removal of apical proximal sesamoid fracture fragments were reviewed. RESULTS: Sixty-four percent of fractures occurred in the hindlimbs and 36% in the forelimbs. Horses with forelimb fractures had a reduced probability of return to racing (67%) compared to those with hindlimb fractures (83%), but the majority (77%) of treated horses recovered to return to race post operatively. Horses with medial forelimb fractures raced at only a 47% rate; those with suspensory desmitis at 63%. Unlike Standardbreds, there was no difference in probability of racing post operatively between horses that had, and had not, raced preoperatively. CONCLUSIONS: Data show that arthroscopic removal of apical proximal sesamoid fracture fragments is successful at restoring ability to race in skeletally mature TB horses without evidence of severe suspensory ligament damage. Prognosis for return to racing is excellent (83%) in horses with hindlimb fractures and good (67%) in those with forelimb fractures. Medial fractures of the forelimb have the worst prognosis. POTENTIAL RELEVANCE: The determination of prognosis for differing sites in TB racehorses should increase knowledge of apical proximal sesamoid bone fractures and improve communication from veterinarian to owner, and trainer, on the potential for arthroscopic restoration of the ability to race.     

A longitudinal study of racing thoroughbreds: performance during the first years of racing

OBJECTIVES: To develop a profile of the racing careers of Thoroughbred horses in south-eastern Queensland, and to examine factors that affect racing during the first years of racing. DESIGN AND PROCEDURE: A longitudinal study using the racing records of a defined cohort of Thoroughbred horses that were born on or within 12 months following 1 August 1991. Data collection commenced in 1996 and will continue until all horses cease racing. In this paper two measures of performance were examined: race earnings during the first year of racing and cumulative proportion of horses still racing up to 2 years after their first start. Univariable and multivariable methods were used to describe and identify factors associated with the performance of these horses. RESULTS: By 31 July 1997, 1804 horses were enrolled in the study including 916, 701, 152 and 35 horses that first raced at 2, 3, 4 and 5 years of age, respectively. During their first year of racing, half the horses earned no more than A$450 from race earnings, and 710 (39.4%) horses earned no money at all. In comparison to poorly performing horses, well-performing horses were more likely to be male, to have started as 2-year-olds and to have had more starts during this year. Of the horses that first started as 2 and 3-year-olds, only 71 and 46% continued racing for at least 1 and 2 years after their first start, respectively. Length of racing life was associated with performance during the first year of racing (number of starts and average earnings per race), and with sex, date of birth and age at first start. CONCLUSIONS: The study confirmed a high wastage among racing Thoroughbreds. As expected, premature retirement from racing was linked to poor performance. During the first year of racing, the race earnings of an estimated 1567 (86.9%) horses were insufficient to cover training costs. The 2-year-old racing cohort outperformed the older racing cohorts in each of the performance measures under investigation. Interpretation of this result, and the long-term effects of 2-year-old racing, was limited by the problem of confounding.     

Race Performance After Laryngoplasty and Ventriculocordectomy in National Hunt Racehorses

Objective— To evaluate the effect of laryngoplasty (LP) on race performance in longer distance (National Hunt) Thoroughbred racehorses. Study Design— Case‐control study. Animals— National Hunt Thoroughbred racehorses (n=71) and race‐matched controls (n=126). Methods— Race records for National Hunt racehorses that had LP and ventriculocordectomy were analyzed and racing performance was compared with race‐matched controls. Results— Sixty‐three of 71 cases were matched with controls. Postoperatively, 78% of cases raced, 47% improved their individual performance and cases were as likely to start in 1 or 3 races as controls. In the 5 preoperative races, case horses earned less prize money than race‐matched controls but there was no difference in prize money earned in 5 postoperative races between groups. Cases started in significantly fewer total (lifetime) races both before and after the date of surgery compared with controls. Conclusions— LP seemingly restored short‐term postoperative racing performance of National Hunt horses to a level comparable with that of a matched control population; however, the career “longevity” of case horses appears to be shorter than that of control horses. Clinical Relevance— LP appears to be a suitable treatment for recurrent laryngeal neuropathy in National Hunt racehorses.     

The risk of severity of limb injuries in racing thoroughbred horses.

A retrospective study was carried out to identify factors which predisposed Thoroughbred horses to severe injuries, as compared to less severe injuries, while racing on New York Racing Association (NYRA) tracks during the period of January 1986 to June 1988. A severe injury was defined as an injury which led to humane destruction of the horse. A less severe injury was defined as a horse which didn't race within 6 months following a muscular, ligament, tendon, or skeletal injury on the racetrack. The data were obtained from the Horse Identification Department records kept by the Chief Examining Veterinarian of NYRA and included 55 severely injured horses and 245 less severely injured horses. Multiple logistic regression analysis was used to identify factors associated with the risk of severe injuries compared to less severe injuries in those horses. There was a significant association between track and the risk of severe injury (horses raced on Belmont and Saratoga were more likely to develop a severe injury compared to horses raced on Aqueduct Main). The track surface was also associated with the risk of severe injury (horses raced on a firm turf had a significantly lower risk of severe injury associated with the track was significantly modified by the track condition (horses raced at Belmont when it was muddy had a significantly increased risk compared to Aqueduct dirt). Horses were more likely to experience severe injury in the early part of the race (less than or equal to 6 furlongs) than the latter part of the race (greater than 6 furlongs). The risk of severe injury decreased with the age of the horse.     

Incomplete Oblique Sagittal Fractures of the Dorsal Cortex of the Third Metacarpal Bone in Six Horses

Objective —To describe incomplete oblique sagittal dorsal cortical fractures of the equine third metacarpal bone, their surgical repair, and subsequent performance of the horses.
Study Design —Retrospective examination of medical records and racing performance.
Animal Population —Six Thoroughbred race horses, 2 to 4 years of age.
Methods —Radiographic confirmation of all fractures preceded general anesthesia and surgical correction. Three fractures were treated by intracortical compression using screws placed in lag fashion, and five fractures were treated by osteostixis. Race records were reviewed for each horse to determine performance after surgery.
Results —Fractures were best observed on palmarodorsal radiographic projections. Three horses treated by intracortical compression returned to racing, but fracture recurred in one horse and was treated by osteostixis. This horse and the other three horses treated by osteostixis raced after surgery.
Conclusions —Horses with incomplete oblique sagittal fractures of the dorsal cortex of the third metacarpal bone can race after surgical management of the fracture by screws placed in lag fashion or osteostixis. The authors' preferred surgical procedure for managing this fracture is osteostixis.
Clinical Relevance —Palmarodorsal radiographic projections of the third metacarpal bone are recommended in young Thoroughbred race horses suspected of having dorsal metacarpal stress fractures.     

Comparison of tracheal aspirates and bronchoalveolar lavage in racehorses. 2. Evaluation of the diagnostic significance of neutrophil percentage

OBJECTIVE: To determine whether diagnosis of airway inflammation, using cut-off percentages for neutrophils, differs when based on samples from tracheal aspirate (TA) and bronchoalveolar lavage (BAL) collected concomitantly from the same racehorse. DESIGN: Retrospective case series of 48 young Thoroughbred and Standardbred racehorses in race training, but showing poor performance. PROCEDURE TA and BAL samples were collected from all horses 1 to 2 h after high-speed treadmill exercise. Aliquots of the retrieved fluid were cytocentrifuged and smears stained with Diff-Quik. The mean percentage of neutrophils was calculated. Diagnostic cut-off points were set at 20% for TA samples and 5% for BAL samples. Agreement in the interpretations between the two techniques was analysed. RESULTS: In 19 of 51 paired samples (37%) there were differences in diagnostic interpretation between TA and BAL samples. Of these, airway inflammation was indicated only by the TA sample in 13 and only by the BAL in 6. CONCLUSION: TA and BAL samples give important information about different regions of the airway, but neither should be used alone for the diagnosis of inflammation of the entire lung. The limitations of these procedures mean that both samples should be collected when it is desired to cytologically evaluate the entire lower airway.     

Evaluation of detailed training data to identify risk factors for retirement because of tendon injuries in Thoroughbred racehorses

OBJECTIVE: To identify the risk factors for premature retirement because of tendon injury in a Thoroughbred racehorse population. ANIMALS: 175 Thoroughbred racehorses (cases) at the Hong Kong Jockey Club that were retired from racing because of tendon injury between 1997 and 2004 and for which the last preretirement exercise was at a fast pace were each matched with 3 control horses that were randomly selected from all uninjured horses that had galloped on the same date as that last exercise episode. PROCEDURES: Training data for all horses were examined. Conditional logistic regression analyses were performed to identify risk factors for retirement from racing attributable to tendon injury. Two multivariable conditional logistic regression models were created; each contained 8 explanatory variables. RESULTS: Compared with control horses, case horses were older at the time of import, accumulated more race distance soon after import, were more likely to have had previous official veterinary or ultrasonographic examinations, raced fewer times during their career, and were in training for a longer period and had exercised at a reduced intensity during the 180-day period preceding the last fast-paced work date. CONCLUSIONS AND CLINICAL RELEVANCE: In addition to identification of risk factors for tendon injury among racing Thoroughbreds, results have suggested that resources focused on obtaining accurate training data may be misdirected in the absence of internationally agreed criteria for incident tendon injury among racehorses. Nevertheless, changes in training intensity and findings of previous clinical examinations could be used to identify horses at risk of tendon injury-associated retirement.