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Background: Musculoskeletal injuries are observed in Thoroughbred racehorses and may become catastrophic. Currently, there are limited methods for early detection of such injuries. Most injuries develop gradually due to accumulated damage, providing the opportunity for early detection. Horses experiencing pain or lameness may exhibit changes in behaviour so the development of an objective, real-time system monitoring horse behaviour may enable detection of bone injuries before catastrophic failure., Objectives: To determine whether intensive observational methods of assessing horse behaviour can be replaced by use of inertial measurement units (IMUs)., Study Design: Validation study assessing IMU use against video observation., Methods: Six hospitalised Thoroughbreds (algorithm training data) and 19 Thoroughbred racehorses in-training (algorithm testing data) were equipped with an IMU placed on the lateral side of both forelimbs (left fore, LF; right fore, RF) and monitored in a stable for 4 h. An algorithm was developed to classify behaviour and then validated against video recordings., Results: Standing was the most prevalent behaviour (LF 88.8%, 95% confidence interval [CI] 88.7-89.0; RF 88.5%, 95% CI 88.4-88.7). IMU classification of recumbent and standing activities showed excellent agreement (sensitivity) with video observation (>98%). This was followed by stepping (LF 89.4%, RF 85.5%) then weight-shifting (LF 54.3%, RF 61.5%). Predictions from the algorithm showed misclassification of 2.5% (LF 5500/225 352, RF 5218/210 170). Excluding standing, misclassification was 6.8% (1705/25 158) and 7.5% (1812/24 077) for the left and right forelimbs, respectively, with pawing and weight-shifting most frequently misclassified., Main Limitations: Increasing the number of horses and types of behaviours observed may improve predictions., Conclusions: IMUs displayed a high sensitivity to movement on a small number of horses, and with further validation they have the potential to effectively monitor behaviour of racehorses in training. However, more sensitive methods may be needed to validate the classification of weight-shifting behaviour. Future studies should evaluate the association between each behaviour and musculoskeletal injury., (© 2022 The Authors. Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.)

Musculoskeletal injuries in racehorses are difficult to detect prior to catastrophic breakdown. Lameness is commonly attributed to orthopaedic pain in horses, therefore, subtle lameness may be a pre-clinical sign of injury and, if identified early, could allow for preventative intervention. Our objective was to determine if facial expressions could be used to detect mild lameness as an indicator of orthopaedic pain in 'fit to race' horses. The Horse Grimace Scale (HGS) and the facial expressions in ridden horses (FEReq), were used to score images (n = 380) of mildly lame (n = 21) and non-lame (n = 17) Thoroughbred horses by two independent observers. Using an Equinosis Lameness Locator ® , the lameness status of each horse was determined according to published thresholds [forelimb lameness (>|14.5 mm|) and hindlimb lameness (>|7.5 mm|)]. Inter and intraobserver reliability were assessed using two-way random-effects models. Univariable associations between lameness and facial expression parameters were identified using logistic and linear regression. Interobserver reliability was moderate (κ 0.45; 95% CI 0.36, 0.55). Horses with moderate mouth strain (HGS) and tense and extended upper lip (FEReq) were less likely to be lame ( p = 0.042 and p = 0.027, respectively). Exposed sclera was associated with lameness ( p = 0.045). Higher orbital tightening (HGS) scores were associated with a lower degree of maximum head amplitude (HDmax) lameness ( p = 0.044). Tension and moderate tension above the eye, for the HGS and FEReq scores, were associated with increasing amplitude of HDmax ( p = 0.048 and p = 0.034, respectively). Inconsistent associations between lameness status and HGS and FEReq scores may limit the potential use of the facial expression for the prediction of mild orthopaedic pain during pre-race lameness examinations. More objective parameters associated with mild orthopaedic pain should be explored.

Fatigue life (FL) is the number of cycles of load sustained by a material before failure, and is dependent on the load magnitude. For athletes, 'cycles' translates to number of strides, with load proportional to speed. To improve previous investigations estimating workload from distance, we used speed (m/s, x) per stride collected using 5 Hz GPS/800 Hz accelerometer sensors as a proxy for limb load to investigate factors associated with FL in a Thoroughbred race start model over 25,234 race starts, using a combination of mathematical and regression modelling. Fore-limb vertical force (NKg -1 ) was estimated using a published equation: Vertical force = 2.778 + 2.1376x - 0.0535x 2 . Joint load (σ) was estimated based on the vertical force, scaled according to the maximum speed and defined experimental loads for the expected variation in load distribution across a joint surface (54-90 MPa). Percentage FL (%FL) was estimated using a published equation for cycles to failure (N f ) summed across each race start: N f  = 10 (σ-134.2)/-14.1. Multivariable mixed-effects linear regression models were generated on %FL, adjusting for horse-level clustering, presented as coefficients; 95%CI. Scaled to the highest joint load, individual starts accrued a mean of 9.34%FL (sd. 1.64). Older age (coef. 0.03; 0.002-0.04), longer race-distances (non-linear power transformed), and firmer track surfaces (ref. Heavy 10: Good 3 coef. 2.37; 2.26-2.48) were associated with greater %FL, and males accrued less than females (p < 0.01). Most variables associated with %FL are reported risk factors for injury. Monitoring strides in racehorses may therefore allow identification of horses at risk, enabling early detection of injury., (© 2022. The Author(s).)

Understanding the relationship between the training practices of Thoroughbred racehorses and race performance is important to ensure advice given to trainers for injury prevention or management is practical and consistent. We assessed associations between intended volume and speed of gallop training (i.e., typical workloads for horses free of injury or other performance limiting conditions) and rest practices on official trainer career and previous season success rates (rate of wins and places, prizemoney per start). Sixty-six Australian Thoroughbred trainers were surveyed. Multivariable negative binomial regression models were employed for the outcomes career and previous season wins and places, and linear regression models for prizemoney per start. Intended training workload was not associated with prizemoney. Pre-trial total galloping distances (≥13.3 m/s) between 7500 m and 15,000 m were associated with a higher rate of career wins, and previous season wins and places per start ( p < 0.05). Slow-speed (13.3-14.3 m/s) galloping distance to trial between 5000 m to 12,500 m was associated with higher rate of career placings per start, with reduced performance over 12,500 m ( p = 0.003). Greater time between race starts was associated with a greater rate of previous season wins and prizemoney per start until three weeks between starts, with decline in performance thereafter ( p < 0.05). Greater frequency of rest breaks was associated with greater prizemoney per start earnt in the previous season ( p ≤ 0.01). These results suggest that modifications to training programs aimed at injury prevention, such as avoiding long galloping distances, should not adversely affect trainer success.

Background: With each stride, galloping horses generate large skeletal loads which influence bone physiology, and may contribute to musculoskeletal injury. Horse speed and stride characteristics are related, but the usefulness of using horse speed and distance travelled as a proxy for stride characteristics is unknown., Objectives: We aimed to determine stride characteristics, their variance and their relationship with speed in horses performing maximally., Study Design: Retrospective cross-sectional analysis of archived data., Methods: Stride characteristics obtained using GPS and inertial sensors in Thoroughbred horses were retrieved. Data per 200 m race segment ('sectionals') for horses competing in races (N = 25,259 race starts) were analysed to determine if speed predicted stride parameters. Multivariable mixed-effects linear regression models were fitted., Results: Mean (±SD) stride length, stride count (number of strides per 200 m), duration and speed were 7.08 ± 0.39 m, 28.32 ± 1.56 strides/200 m, 0.43 ± 0.02 s/stride and 16.63 ± 1.04 m/s across all sectionals and starts. Speed and stride length decreased, and stride count increased with race progression (P < 0.001). Male sex, greater race distance, better finishing position and firmer track surfaces were associated with less strides per 200 m and longer stride durations., Main Limitations: Lack of an independent party validation of the measurement system used in this study., Conclusions: There was a substantial inter-horse variation in stride parameters, with speed predicting half or less of this variation. Speed alone does not fully explain stride characteristics in horses. Future studies aimed at investigating the impact of gait on bone biology and pathology would benefit from accounting for stride characteristics (eg length and duration)., (© 2020 EVJ Ltd.)

Background: As myosin heavy chain (MyHC) profile of muscle fibres is heavily influenced by neural input, changes in MyHC expression are expected in horses clinically affected with recurrent laryngeal neuropathy (RLN) yet, this has not been thoroughly investigated., Objectives: To describe the changes in MyHC and fibre diameter in left cricoarytenoideus dorsalis (L-CAD) muscle of horses with clinical signs of RLN., Study Design: Observational cohort study., Methods: Immunohistochemistry was used to assess the MyHC-based fibre-type proportion, size and grouping in the L-CAD of 10 Thoroughbred horses, five clinically affected with RLN and five unaffected controls based on resting endoscopic examination. The Mann-Whitney U test was used to compare the two groups., Results: Compared to controls (of mean age 3.0 ± 1.7 years) which only expressed type I, IIA and IIX MyHC, the L-CAD of affected horses (of mean age 2.8 ± 0.8 years) had obvious fibre-type grouping, and despite apparent compensatory hypertrophy of a small number of fibres, a decrease in overall fibre diameter (median difference -35.2 µm, 95% CI -47.4 to -7.9, P = .02) and diameter of type IIA fibres (median difference -46.8 µm, 95% CI -52.1 to -5.0, P = .03) was observed. Anti-fast MyHC (MY32) cross-immunoreacted with embryonic-MyHC. Whereas MY32-positive fibres were identified as type IIX in controls, in affected horses these fibres were less than 50 µm diameter with internal nuclei and were MYH3-positive for embryonic myosin indicating depletion of type IIX fibres, yet active regeneration and fibre renewal., Main Limitations: Small sample size that did not include subclinical cases. Fibre size and appearance rather than staining colour were relied upon to differentiate embryonic from type IIX MyHC., Conclusions: Horses clinically affected with RLN have overall atrophy of fibres, loss of IIX fibres and expression of embryonic myosin indicating regenerative capacity. Despite hypertrophy of some remaining fibres, the overall decline in the bulk of fibres, including those most fatigue-resistant, may be the critical change that results in failure to maintain arytenoid abduction during exercise although direct comparison to subclinical cases is needed to confirm this., (© 2020 EVJ Ltd.)

Lymphoma is the most common intestinal neoplasm in horses, but its clinical-pathological features are poorly characterized. Primary intestinal lymphoma was diagnosed in 20 horses on biopsy samples and further confirmed by postmortem examination in 16 cases. Lymphoma was found in the small intestine in 12 of 20 (60%), in the colon in 5 of 20 (25%), and in both small and large intestines in 3 of 20 (15%) cases. Gross findings included thickening of the intestinal wall (45%), mural nodules or masses (30%), and both thickening and nodules (10%). Cases were classified according to the human World Health Organization classification as enteropathy-associated T-cell lymphoma (EATL) type 1 (40%), EATL type 2 (45%), and T-cell-rich large B-cell lymphoma (TCRLBCL) (15%). With respect to histologic grade, 70% of cases were grade 1 and 30% were grade 2. Of EATLs, the infiltrate was mucosal only (12%), mucosal and submucosal (53%), or transmural (35%). EATL1 was submucosal to transmural (2/8 and 6/8), EATL2 was mucosal to submucosal (3/9 and 6/9), and TCRLBCL was always transmural. Epitheliotropism was present in most EATLs and characterized by single-cell infiltrates within the epithelium in EATL1 and intraepithelial clusters or plaques in EATL2. Median survival was 25 days for EATL1, 90 days for EATL2, and 187.5 days for TCRLBCL; differences were not statistically significant. Of the EATLs, grade 1 had a median survival of 60 days and grade 2 had a median survival of 25 days; differences were not statistically significant.

Background: Musculoskeletal injuries (MSI) in racehorses are commonly due to bone fatigue, a function of the number of cycles (strides) and the magnitude of load applied to the limb. These parameters can be estimated using speed and distance, with greater than 6000 m/month at a gallop (>14 m/s), in combination with canter distances greater than 44,000 m/month, reported to increase fracture risk. Despite their importance, there are limited data on the distances and speeds horses are exposed to during training., Objectives: Estimate training volume at different speeds undertaken by Australian Thoroughbred racehorses., Study Design: Cross-sectional study., Methods: Registered trainers (n = 66) in Victoria, Australia were surveyed. Questions were designed to assess the full training workload from initial pre-training to training performed to achieve and maintain race fitness, as well as information on rest periods. Descriptive analyses were stratified by trainer- and horse-level factors, with assessment of variance within and between groups. Cluster analyses were used to identify similar workload intensity groups., Results: Horse-level factors (age, targeted race distance) were associated with workload (younger

Background: Subchondral bone injury at the palmar/plantar aspect of the condyles of the third metacarpal/metatarsal bone (MC/MT3) commonly causes lameness and poor performance in racehorses. Injury occurs due to repetitive loading, the magnitude of which may be influenced by the position of the distal phalanx relative to the ground surface, i.e. the solar angle. The association of solar angle and injury at the palmar/plantar condyles of distal MC/MT3 therefore warrants investigation., Objectives: Investigate the relationship between solar angle and radiopharmaceutical uptake at the palmar/plantar aspect of distal MC/MT3 on scintigraphic images of racehorses., Study Design: Retrospective case-controlled study., Methods: Scintigraphic images of Thoroughbred racehorses presented for poor performance or lameness were graded for intensity of radiopharmaceutical uptake in the palmar/plantar aspect of distal MC/MT3. Solar angle was graded (positive, neutral or negative), referring to the angle of the solar plane of the distal phalanx relative to the ground surface. Repeatability of solar angle (n = 1226 limbs) and agreement with objective radiographic evaluation (n = 52 limbs) were evaluated. Prescintigraphy performance data were collected from race records. Associations between solar angle, performance and radiopharmaceutical uptake were investigated using multivariable logistic regression., Results: Repeatability of scintigraphic solar angle grading (κ = 0.89, 95% CI 0.87-0.91) and agreement of scintigraphic and radiographic solar angle (κ = 0.88, 95% CI 0.75-0.97) were excellent. Horses that performed best prior to presentation were more likely to have both greater radiopharmaceutical uptake and a neutral/negative solar angle. When controlling for prior performance, horses with neutral/negative forelimb solar angle were twice as likely to have moderate/marked radiopharmaceutical uptake than horses with positive solar angle (P<0.02). Horses with negative hindlimb solar angle were six times more likely to have moderate/marked radiopharmaceutical uptake than horses with positive/neutral solar angle (P<0.001)., Main Limitations: Population bias due to preselected hospital population., Conclusions: Both solar angle and race performance are independently associated with increased bone activity in the palmar/plantar aspect of the third metacarpal/tarsal condyles. The Summary is available in Portuguese - see Supporting Information., (© 2019 EVJ Ltd.)

Long bone fractures in racehorses may present as stress fractures which have a good prognosis, or complete fractures, which often result in a fatal outcome. In order to identify differences in modifiable management practices that may contribute to these outcomes, racing histories of horses with humeral or tibial fractures and of matched controls were examined. A retrospective case-control study of Australian Thoroughbred racehorses diagnosed with a fracture of the humerus or tibia by scintigraphy or at post-mortem between 2002 and 2016 was undertaken. Control horses were matched from the same race or trial on age and sex. Statistical analysis was performed using conditional logistic regression, χ 2 and Mann-Whitney U tests. More humeral fractures than tibial fractures were fatal (12/47, 26% vs. 3/35, 8.6%, P = 0.049). No differences in pre-injury racing histories were observed between cases and controls for humeral and tibial fractures. Both humeral and tibial fracture case horses were younger than the registered Thoroughbred racing population (P < 0.001), but horses sustaining humeral fractures were older than those with tibial fractures (3.3 ± 0.9 vs. 2.8 ± 0.8 years, P = 0.005) yet raced fewer times prior to the injury (0.5 ± 1.1 vs. 1.3 ± 1.7 races, P = 0.009). Horses with fatal humeral fractures were less likely to have raced than those with non-fatal humeral fractures (16.7% vs. 55.6%, P = 0.02). In conclusion, tibial and humeral fractures occur in young racehorses, and humeral fractures are more likely to be fatal in those with the least exposure to trialling and racing., (Copyright © 2019. Published by Elsevier Ltd.)

Little is known about the types of surfaces used during training of Thoroughbred racehorses or methods of exercise used in addition to ridden track-work. Our aims were to (1) describe the types of surfaces used in the training of Thoroughbred racehorses and to (2) identify alternative approaches used to exercise horses in addition to, or in place of, ridden overground track-work. Information regarding surface and alternative exercise methods was collected as part of an in-person survey of training practices of 66 registered Thoroughbred trainers in Victoria, Australia. Sand and synthetic surfaces were used by 97% and 36% of trainers respectively for slow-workouts, with galloping on turf training tracks used in training regimens by 82% and synthetic by 58% of trainers. Of those trainers utilising turf tracks, only 34% of gallop training was completed on turf despite turf being the predominant racing surface. Almost 90% of trainers used alternatives to ridden exercise. There is substantial variation in training surface used and alternative types of exercise undertaken by Victorian trainers. Future research should focus on how such practices relate to injury risk, particularly as it relates to the importance of musculoskeletal adaptation to specific race-day surfaces.