The association between Thoroughbred racehorse training practices and musculoskeletal injuries in Victoria, Australia.

Catastrophic musculoskeletal injuries (CMI) in horses are associated with both too little and too much high-speed exercise. In order to advise trainers on training and management strategies that minimize the risk of musculoskeletal injury (MSI), a better understanding of how training practices affect MSI in racehorses is needed. Data from prospective studies relating training data and MSI are complicated by the gradual development of pathology and the effect of this on the ability of horses to train consistently prior to the identification of an injury. To circumvent this, 66 Australian Thoroughbred trainers were surveyed on their intended training practices, including rest, pre-training, and race-fit practices. Associations between intended training practices and catastrophic and non-catastrophic race day MSI outcomes in two-year-old and mature (≥three-year-old) horses were assessed using multivariable negative binomial regression models. The incidence of two-year-old race day MSI was lower for trainers who preferred shorter times (weeks) to trial, less time in fast work pre-trial (p = 0.003), shorter, more frequent rest periods (p < 0.01) and higher amounts of fast work at 15.5-16.7 m/s once race-fit (p = 0.001). The incidence of mature horse race day MSI was lower for trainers who preferred longer rest periods (p = 0.026) and a high-volume pre-trial training strategy comprising a high volume of slower speed gallop training and longer times to trial compared to fast and light training programs (p = 0.004) for their mature horses, in addition to higher amounts of fast work at 15.5-16.7 m/s for their race-fit two-year-olds (p = 0.012). Race day CMI incidence was lower for trainers who preferred lower volumes of fast gallop work for their race-fit mature horses (p < 0.05). These results suggest that two-year-old training practices could affect MSI risk later in a horse's career, and that age and stage in training (pre-trial, race-fit) are important considerations when developing training practices to minimize the risk of MSI.

Poor Association between Facial Expression and Mild Lameness in Thoroughbred Trot-Up Examinations.

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.

Changes in Thoroughbred speed and stride characteristics over successive race starts and their association with musculoskeletal injury.

BACKGROUND: Certain stride characteristics have been shown to affect changes in biomechanical factors that are associated with injuries in human athletes. Determining the relationship between stride characteristics and musculoskeletal injury (MSI) may be key in limiting injury occurrence in the racehorse. OBJECTIVES: This study aimed to determine whether changes in race day speed and stride characteristics over career race starts are associated with an increased risk of MSI in racehorses. STUDY DESIGN: Case-control study. METHODS: Speed, stride length, and stride frequency data were obtained from the final 200 m sectional of n = 5660 race starts by n = 584 horses (case n = 146, control n = 438). Multivariable joint models, combining longitudinal and survival (time to injury) analysis, were generated. Hazard ratios and their 95% confidence intervals (CI) are presented. RESULTS: The risk of MSI increased by 1.18 (95% CI 1.09, 1.28; P < 0.001) for each 0.1 m/s decrease in speed and by 1.11 (95% CI 1.02, 1.21; P = 0.01) for each 10 cm decrease in stride length over time (career race starts). A more marked rate of decline in speed and stride length was observed approximately 6 races prior to injury. Risk of MSI was highest early in the horse's racing career. MAIN LIMITATIONS: Only final sectional stride characteristics were assessed in the model. The model did not account for time between race starts. CONCLUSIONS: Decreasing speed and stride length over multiple races is associated with MSI in racehorses. Monitoring stride characteristics over time may be beneficial for the early detection of MSI.

Catastrophic Musculoskeletal Injuries in Thoroughbred Racehorses in Uruguay, 2011-2017.

Catastrophic musculoskeletal injuries (CMI) pose a major welfare concern to horses and their riders, yet limited data are available describing their occurrence in South America. Using a retrospective cohort and case-control design, the objective of the study was to determine the incidence of CMI for Thoroughbreds in training and racing, and associated horse-level risk factors in Uruguay. Seventy-seven Thoroughbreds sustained a CMI, 37 of which were age- and sex-matched to 111 control horses in the same race. Training and racing data from 2011 to 2017 were collected. Incidence of race day CMI per 1,000 race starts and training CMI incidence per 100 horse months were calculated using Poisson regression. Univariable logistic regression was used to assess relationships between race history and occurrence of CMI by fracture location, and multivariable for all fracture locations. Overall race day incidence of CMI was 0.42 per 1,000 race starts (95% CI 0.29, 0.60). The incidence of CMI in training was 0.059 per 100 horse months. Twenty-nine percent (22/77) of horses that sustained a CMI had not raced prior. Most fractures were of the forelimbs (80.3%). There were 32 (41.6%) distal and 39 (50.6%) proximal limb fractures. The risk of CMI was greater for horses with fewer places (P = .001), and greater time between the previous race and the race in which CMI occurred (P = .020). The rate of race day CMI was low, despite Uruguay being a racing jurisdiction with policies and risk factors associated with greater CMI rates compared to other jurisdictions. Lightly raced horses with long periods since their previous race start should be monitored closely.

Association of Thoroughbred Racehorse Workloads and Rest Practices with Trainer Success.

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.

Microstructural properties of the proximal sesamoid bones of Thoroughbred racehorses in training.

BACKGROUND: Proximal sesamoid bone fractures are common catastrophic injuries in racehorses. Understanding the response of proximal sesamoid bones to race training can inform fracture prevention strategies. OBJECTIVES: To describe proximal sesamoid bone microstructure of racehorses and to investigate the associations between microstructure and racing histories. STUDY DESIGN: Cross-sectional. METHODS: Proximal sesamoid bones from 63 Thoroughbred racehorses were imaged using micro-computed tomography. Bone volume fraction (BVTV) and bone material density (BMD) of the whole bone and four regions (apical, midbody dorsal, midbody palmar and basilar) were determined. Generalised linear regression models were used to identify the associations between bone parameters and race histories of the horses. RESULTS: The mean sesamoid BVTV was 0.79 ± 0.08 and BMD was 806.02 ± 24.66 mg HA/ccm. BVTV was greater in medial sesamoids compared with lateral sesamoids (0.80 ± 0.07 vs 0.79 ± 0.08; P < .001) predominantly due to differences in the apical region (medial-0.76 ± 0.08 vs lateral-0.72 ± 0.07; P < .001). BVTV in the midbody dorsal region (0.86 ± 0.06) was greater than other regions (midbody palmar-0.79 ± 0.07, basilar-0.78 ± 0.06 and apical-0.74 ± 0.08; P < .001). BVTV was greater in sesamoids with more microcracks on their articular surface (Coef. 0.005; 95% CI 0.001, 0.009; P = .01), greater extent of bone resorption on their abaxial surface (Grade 2-0.82 ± 0.05 vs Grade 1-0.80 ± 0.05 or Grade 0-0.79 ± 0.06; P = .006), in horses with a low (0.82 ± 0.07) or mid handicap rating (0.78 ± 0.08) compared with high rating (0.76 ± 0.07; P < .001), in 2- to 5-year-old horses (0.81 ± 0.07) compared with younger (0.68 ± 0.08) or older horses (0.77 ± 0.08; P < .001) and in horses that commenced their racing career at less than 4 years of age (0.79 ± 0.08 vs 0.77 ± 0.77; P < .001). BMD was greater in the midbody dorsal (828.6 ± 19.6 mg HA/ccm) compared with other regions (apical-805.8 ± 21.8, midbody palmar-804.7 ± 18.4 and basilar-785.0 ± 17.1; P < .001), in horses with a handicap rating (low-812.1 ± 20.0, mid-821.8 ± 21.3 and high-814.6 ± 19.4) compared with those with no rating (791.08 ± 24.4, P < .001), in females (806.7 ± 22.0) and geldings (812.2 ± 22.4) compared with entires (792.7 ± 26.2; P = .02) and in older horses (<2-year-old-763.7 ± 24.8 vs 2- to 5-year-old-802.7 ± 23.4, and 6- to 12-year-old-817.8 ± 20.0; P = .002). MAIN LIMITATIONS: Data were cross-sectional. CONCLUSIONS: Densification of the proximal sesamoid bones is associated with the commencement of racing in younger horses and the presence of bone fatigue-related pathology. Lower sesamoid BVTV was associated with longevity and better performance.

Variation in GPS and accelerometer recorded velocity and stride parameters of galloping Thoroughbred horses.

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).

Barriers to entering race training before 4 years of age for Thoroughbred horses born in the 2014 Australian foal crop.

Currently, there is a paucity of data on the barriers for Australian Thoroughbred horses transitioning from stud farm to racetrack. This paper reports the reasons why horses failed to enter race training and documents their exit destinations. Biographical records of Australian Thoroughbred horses born in 2014 were investigated to determine the number of horses that had not officially entered race training by the start of the 4-year old racing season (1 August 2018). Of the 13,677 foals born in 2014, 66% had commenced training and 51% had raced before the beginning of their 4-year-old season in Australia. A sampling frame based on the post code of the premises where foals were born and records from Racing Australia were used to select a geographically representative sample of the 2014 Australian Thoroughbred foal crop (n = 4,124). From the population eligible for sampling 1,275 horses that had not entered training were enrolled in the survey and their breeders were sent an online questionnaire with follow-up phone calls for those who had not responded. Of the 633 responses (50% of 1275) the most frequent outcomes for horses were: death (38%, n = 239), participation in the racing industry in their 4-year old racing season (24%, n = 154) and retirement (16%, n = 100) either as Australian Stud Book (ASB) bloodstock (n = 17), or as horses rehomed outside the Thoroughbred industry (n = 83). Illness or injury was the most frequent reason for horses not entering race training that were ASB bloodstock, rehomed or deceased. There was a loss of traceability at the point of sale with most horses sold at 1 year of age. This study provides important information on the reasons, alternative outcomes and gaps in traceability for horses not entering training prior to the 4-year-old racing season.

pH-Responsive Transferrin-pHlexi Particles Capable of Targeting Cells in Vitro.

Targeting nanoparticles to specific cellular receptors has the potential to deliver therapeutic compounds to target sites while minimizing side effects. To this end, we have conjugated a targeting protein, holo-transferrin (holo-Tf), to pH-responsive polymers, poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) and poly(2-(diethylamino)ethyl methacrylate)-ran-poly(2-(diisopropylamino)ethyl methacrylate (PDEAEMA-r-PDPAEMA). These protein-polymer hybrid materials were observed to self-assemble when the pH is increased above the pKa of the polymer. We demonstrate that their response to pH could be tuned depending on the polymer constituent attached to holo-Tf. Importantly, the targeting behavior of these nanoparticles could be maximized by tuning the density of holo-Tf on the nanoparticle surface by the introduction of a (PDEAEMA-r-PDPAEMA)-b-poly(ethylene glycol) (PEG) copolymer.

Probing Endosomal Escape Using pHlexi Nanoparticles.

The effective escape of nanocarriers from endosomal compartments of the cell remains a major hurdle in nanomedicine. The endosomal escape of pH-responsive, self-assembled, dual component particles based on poly[2-(diethylamino)ethyl methacrylate)(PDEAEMA) and poly(ethylene glycol)-b-poly[2-(diethylamino)ethyl methacrylate) (PEG-b-PDEAEMA) has been recently reported. Herein, we report that polymer molecular weight (Mn ) can be used to tune endosomal escape of nanoparticle delivery systems. PDEAEMA of Mn 7 kDa, 27 kDa, 56 kDa and 106 kDa was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization and co-assembled with PEG-b-PDEAEMA (16 kDa) via nanoprecipitation. All particles had similar size, displayed pH-responsive behaviour, and low toxicity regardless of molecular weight. Ovalbumin was loaded in the particles to demonstrate loading and release capabilities and as a marker to study internalization and endosomal escape. Association and endosomal escape was found to depend on molecular weight, with enhanced escape observed for high Mn PDEAEMA: 42% of cells with particle induced endosomal escape for 106 kDa nanoparticles, compared to minimal escape for 7 kDa particles. The results show that a simple variation in molecular weight can enhance the endosomal escape of polymeric carriers, and thus improve their effectiveness for intracellular delivery of therapeutics.

Self-assembling dual component nanoparticles with endosomal escape capability.

This study reports a novel nanoparticle system with simple and modular one-step assembly, which can respond intelligently to biologically relevant variations in pH. Importantly, these particles also show the ability to induce escape from the endosomal/lysosomal compartments of the cell, which is integral to the design of efficient polymeric delivery systems. The nanoparticles were formed by the nanoprecipitation of pH-responsive poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) and poly(2-(diethylamino)ethyl methacrylate)-b-poly(ethylene glycol) (PDEAEMA-b-PEG). Rhodamine B octadecyl ester perchlorate was successfully encapsulated within the hydrophobic core of the nanoparticle upon nanoprecipitation into PBS at pH 8. These particles disassembled when the pH was reduced below 6.8 at 37 °C. Cellular experiments showed the successful uptake of the nanoparticles into the endosomal/lysosomal compartments of 3T3 fibroblast cells. The ability to induce escape from the endosomes was demonstrated by the use of calcein, a membrane-impermeable fluorophore. The modular nature of these particles combined with promising endosomal escape capabilities make these dual component PDEAEMA nanoparticles useful for drug and gene delivery applications.