Endurance Rides Research Articles

Physiological stress responses in horses participating in novice endurance rides

Horses participating in endurance events encounter enormous physical challenges. Heart rate (HR) and heart rate variability (HRV) have been reported before and after endurance rides, but these have not been determined during the rides. Moreover, the modulation in HRV and haematology in horses with different ride results (completed a course or disqualified due to irregular gait) have not been elucidated. Therefore, this study aimed to investigate changes in HR, HRV, and haematological parameters during novice endurance rides and to compare these parameters between horses that successfully completed the course (SC) or were disqualified for irregular gait (FTQ-GA). Beat-to-beat (RR) intervals of 16 healthy horses (aged 6–14 years) were recorded before and throughout the approximately 40 km endurance event. Blood samples were taken at the pre-ride inspection and after passing each veterinary inspection. HRV and haematology measures were determined from nine SC and seven FTQ-GA horses. Horses with different ride results demonstrated distinctive physiological stress responses. Increases in PCV, RBC, WBC and neutrophils after completing the ride were found only in SC horses, implying that they were ridden with greater effort than FTQ-GA horses. A reduction in HRV during warm-up, followed by a significant reduction during the first and second riding phases, was observed. HRV returned to baseline at the compulsory rest period of both phases. FTQ-GA horses experienced lower RR intervals, RR triangular index, modified deceleration capacity, very-low-frequency band, and parasympathetic nervous system index, coinciding with higher HR and sympathetic nervous system and stress indices than SC horses. These results indicated that endurance horses revealed a shift toward sympathetic activity during the ride. Lower parasympathetic activity in FTQ-GA horses suggests they were under more stress or discomfort than SC horses in novice endurance rides. These results have welfare implications, indicating the need for additional rest breaks in FTQ-GA horses.

Immunology of Physical Exercise: Is Equus caballus an Appropriate Animal Model for Human Athletes?

Domestic horses routinely participate in vigorous and various athletic activities. This enables the horse to serve as a model for studying athletic physiology and immunology in other species, including humans. For instance, as a model of physical efforts, such as endurance rides (long-distance running/aerobic exercise) and races (anaerobic exercise), the horse can be useful in evaluating post-exercise response. Currently, there has been significant interest in finding biomarkers, which characterize the advancement of training and adaptation to physical exercise in the horse. The parallels in cellular responses to physical exercises, such as changes in receptor expression and blood cell activity, improve our understanding of the mechanisms involved in the body's response to intense physical activity. This study focuses on the changes in levels of the pro- and anti-inflammatory cytokines and cellular response in the context of post-exercise immune response. Both the direction of changes in cytokine levels and cellular responses of the body, such as proliferation and expression of surface markers on lymphocytes, monocytes and neutrophils, show cross-functional similarities. This review reveals that horses are robust research models for studying the immune response to physical exercise in human athletes.

Metabolic effects of training endurance horses in a field setting

Abstract Changes in serum biochemistry and skeletal muscle of horses in response to individual endurance rides of varying distance have been reported, as have the effects of submaximal treadmill training. This study evaluated the effects of a controlled field endurance training programme on energy metabolism. Five Arabian horses 6.8 ± 2.0 years (mean ± standard deviation) were trained for 16 weeks over progressively longer distances. The biceps femoris, triceps long head, and semitendinosus muscles were biopsied before and after 4-weekly runs of 10, 20 and 30 miles, respectively, and before and after 10, 20, 30 and 50 miles of a fourth run at the end of the training programme to measure 3-hydroxyacyl-CoA-dehydrogenase (HAD) and succinate dehydrogenase (SDH) activities and triglyceride (TG) and glycogen concentrations in those biopsies. Blood samples were obtained simultaneously to measure serum TG, free fatty acid (FFA), glycerol, glucagon, insulin, and cortisol concentrations. Data were analysed using RM-ANOVA for effects of training and distance. was considered significant. Training increased resting glycogen and TG concentrations in the biceps (, ), triceps (, ) and semitendinosus (, ), respectively. Both HAD and SDH activities increased in the biceps femoris (; ) and triceps (; ), respectively, but not in the semitendinosus. There was no training effect detected on serum hormone responses to exercise distance although serum glycerol (), glucagon () and cortisol () concentrations increased with increasing run distance, while insulin concentration decreased (). Glucagon and cortisol concentrations were correlated (r = 0.67; ). Serum TG decreased with exercise but at a slower rate following training, and serum FFA were higher during exercise following training when compared to the partially trained state. Overall, endurance training enhanced peripheral mobilisation of fat and its utilisation by working muscle, and resting muscle glycogen stores increased.

Pre-Ride Biomarkers and Endurance Horse Welfare: Analyzing the Impact of the Elimination of Superoxide Dismutase, δ-Aminolevulinic-Dehydratase, Thiobarbituric Acid Reactive Substances, Iron, and Serum Amyloid A Levels in Elite 160 km Endurance Rides.

High elimination rates and concerns for horse welfare are important issues in endurance riding. Improved understanding of the causes of elimination could increase completion rates in this sport. We have identified pre-ride laboratory risk factors that enable an assessment of potential elimination before the ride. A longitudinal cohort study was performed among 49 healthy horses competing in the 160 km endurance ride at the 2016 World Championship of Endurance Riding in Samorin/Slovakia. Blood samples were taken before the event. For statistical evaluation, horses were categorized into three groups: finishers, lame horses, and metabolically eliminated horses. Risk factors were calculated for each group using multinominal logistic regression. δ-Aminolevulinic-dehydratase (ALAD), thiobarbituric acid reactive substances (TBARSs), iron, and serum amyloid A (SAA) were measured and did not show an impact on the race outcome, but elevated pre-ride superoxide dismutase (SOD) was shown to have an effect on lameness elimination (p = 0.011). It might serve as an indicator for withdrawing horses at risk of later elimination before endurance rides, ultimately resulting in lower elimination rates and an increase in overall horse welfare.

A description of veterinary eliminations within British National Endurance rides in the competitive season of 2019

Veterinary eliminations within the equestrian sport of endurance have predominantly been evaluated based on data from international competitions. However, in order to take part in international competition, each horse and rider must qualify by completing rides under their national federation. The aim of this study was to analyse the competitive data and veterinary eliminations, specifically lameness, from competitions run by the British governing body of endurance: Endurance GB, during the 2019 competitive season. Competitive results for 765 ride starts from seven different ride venues were evaluated; 81.6% (n=624) horses successfully completed the rides, with the remaining 18.4% (n=141) failing to complete the ride. The majority of horses that were unsuccessful were eliminated for lameness at veterinary inspections (n=83; 58.9%). Horses competing in single loop rides (up to 55 km rides) had a success rate of 88.6% (n=624), in contrast, horses competing in rides of three loops or more (>80 km rides) reported a decreased success rate of 61.8% (n=81). Hindlimb lameness was identified more frequently (n=50; 60.2%) compared with forelimb lameness (n=33; 39.8%). Further consideration should be given to the differences between single loop rides, where a higher percentage are presented to the veterinary panel as lame prior to the start, and multi loop rides, where a higher percentage of horses are eliminated lame during the ride and potential risk factors for the increased prevalence of hindlimb lameness observed.

Factors associated with completion of Fédération Équestre Internationale endurance rides (2012–2019): Modelling success to promote welfare-oriented decisions in the equestrian sport of endurance

Endurance riding is a popular equestrian sport organised at the international level by the Fédération Équestre Internationale (FEI). The sport involves prolonged exercise at speed over significant distances, which puts a substantial load on equine athletes’ musculoskeletal systems and metabolism and contributes to the risk of injuries and other veterinary problems. The FEI employs a system of in-ride veterinary inspections aimed at early detection of such problems and elimination of horses unfit to continue in the ride. To date, risk factors for elimination due to irregular gait or metabolic problems have been the primary focus of scientific enquiry. The present study is the first large-scale multivariable study to report factors associated with the positive outcome of endurance rides – their successful completion. This retrospective observational cohort study used data from the FEI’s Global Endurance Database. The study cohort included 74,629 starts made by 21,346 unique horses in one-day international-level competitions held worldwide between July 2012 and December 2019. Forty-one potential factors identified based on previous studies and a priori hypotheses were considered in the analysis. Univariable and multivariable logistic regression analyses were performed to investigate associations between ride completion and predictor variables and their interactions. The study identified 19 factors and four interactions associated with an increased or decreased likelihood of successful ride completion. High competition frequency (fewer days over mandatory out of competition period; Wald χ2 71.35, P-value <0.0001), fast riding speed (236.57, <0.0001), upward changes in competition level and riding speed between two successive rides (103.59, <0.0001 and 87.60, <0.0001) were associated with a decrease in the likelihood of ride completion. These factors can be effectively regulated by appropriate rules and considered by athletes when planning competition schedules, preparing ride strategies, or indeed during the ride itself. Other identified factors, including horse and rider age, sex, completions and eliminations history, contribute to an estimate of the likelihood that a particular combination completes a ride and thus can aid veterinarians at veterinary inspections as additional inputs supporting their decision-making when assessing horses’ fitness to continue in the competition. The study’s main limitation is an absence of data on national-level rides. Such data and data on training and veterinary histories remain difficult to access and were unavailable for the analysis. The present study’s results demonstrate that shifting the focus to modelling the positive outcome is a valuable approach offering evidence-based recommendations for good horsemanship, better-informed veterinary inspections, and welfare-oriented rules.

Age and Hydration of Competing Horses Influence the Outcome of Elite 160 km Endurance Rides

High elimination rates and the concern for horse welfare are important issues in endurance riding. An improved understanding of the causes of elimination could increase completion rates in this sport. We have identified pre-ride risk factors that allow an assessment of potential elimination before the ride. A longitudinal cohort study was performed among 49 healthy horses competing in the 160 km endurance ride at the 2016 World Championship of Endurance Riding in Samorin/Slovakia. Blood samples were drawn before the ride. For statistical evaluation, horses were categorized in three groups: finishers, lame and metabolically eliminated horses. Risk factors were calculated for each group using multinomial logistic regression. A 1% increase in hematocrit levels was associated with a higher OR for elimination (lameness: OR 1.26, p = 0.017; metabolic: OR 1.34, p = 0.010). Furthermore, increased potassium values correlated negatively with the race outcome. For a 1 mmol/l increase in potassium, the lameness OR was 4.21, p = 0.039 and metabolic OR was 1.15, p = 0.848. Eight-year-old horses had a 100% elimination rate and survival analyses showed a significantly higher hazard for elimination (p = 0.025). We thus conclude that age and hydration affect the outcome of elite endurance rides. Further investigation of age as a risk factor seems to be clinically relevant and adjustments of FEI qualification modes may be appropriate.

Plasma Activin A and Decorin in Exercised Purebred Arabian Horses – Preliminary Study

Development of the musculoskeletal system occurs, in part, through an impact on regulatory proteins, such as activin A and decorin. Activin A induces atrophic effects on skeletal muscle, and decorin regulates the formation of connective tissue proteins like collagen and elastin in tendons and ligaments. The aim of this study was to evaluate the influence of different intensities of exercise on blood plasma activin A and decorin concentrations in horses. Ten young purebred Arabian horses were subjected to routine training sessions on a racetrack, and another 11 adult horses of the same breed participated in endurance rides. Race horses were examined during gallop tests over a distance of 1200 m and endurance horses at distances from 20 to 80 km. Blood samples were collected at rest and after exercise to determine plasma concentrations of activin A, decorin and cortisol. Despite differences in the intensity of exercise, the plasma decorin concentration remained unchanged, and activin A tended to decrease in endurance horses only. The exercise-induced changes in plasma activin A concentrations correlated with the covered distance (r = -0.43; P < .05), but not with the changes in cortisol values. Further studies are needed to confirm the usefulness of plasma activin A as a potential indicator of a horse's endurance performance.

Epidemiology and risk factors for eliminations from Fédération Equestre Internationale endurance rides between 2004–2015 in Italy

There is limited information on risk factors for elimination from endurance rides and changes over the years. The objectives of this study were to describe elimination for irregular gait and metabolic reasons from Fédération Equestre Internationale (FEI) endurance rides in Italy (2004–2015) and to assess risk factors and to investigate changes in elimination rates and speed over the long term.Data for FEI endurance rides were collected from three websites. Year, month, day, location, class (Concours de Raid d’Endurance International [CEI]*/**/***), restriction to young riders, distance (km), number of starters, horses’ age and breed, and average finish speed for each horse were recorded. Horses were classified as completed, retired or eliminated for irregular gait, metabolic or other reasons. Environment data were obtained from the Il Meteo website. Descriptive data were summarized, and univariable analyses and multivariable logistic regression analyses were performed to investigate risk factors. The chi-squared test and one-way or Friedman analysis of variance (ANOVA) were used to assess differences between years. Variables associated with elimination for irregular gait were the number of starters, age of the horse, classes, minimum temperature and presence of rain; those associated with elimination for metabolic reasons were the number of starters, classes, horse breed and minimum temperature. Average finish speed increased over the years but the elimination frequency changed only for metabolic reasons, with a higher percentage at the beginning of the study period. This study was conducted in Italy and the results may not be applicable globally; speed was available only for horses that completed the competition. Average finish speed increased over the years but the percentage of eliminations remained stable after 2007. Training, nutrition, previous injuries and treatments are likely to contribute to problems occurring during the ride, and investigation of these factors would be desirable.

Plasma Apelin Concentration in Exercised Horses: Preliminary Study

Physical effort is one of the key aspects of keeping horses in good condition. The condition of the animal is reflected by multiple blood parameters. The newly discovered cytokine–apelin can pose one of them, however, so far, has not been studied in the horse population. Apelin is produced by adipocytes and myocytes and plays an important role in the energy metabolism of the body through the influence, for example, on the process of adipogenesis and lipolysis. The aim of this study was to investigate if physical effort of various intensity affects the plasma concentration of apelin in horses. The study involved 20 purebred Arabian horses divided into two groups. The first group included 10 race horses, aged 3 years, and second group included 10 horses aged from 6 to 12 years, used in endurance rides. Blood samples were collected from each horse at rest and after exercise. The concentrations of apelin, lactic acid, cortisol, uric acid (UA), triacylglycerols, total plasma protein, and glucose were determined in plasma samples. Race training sessions induced significant decreases in plasma apelin concentrations (P < .05). In endurance horses, significant correlations were found only between exercise-induced changes of apelin and cortisol (r = 0.55) and apelin and UA (r = 0.67) concentrations. In conclusion, the concentration of apelin in equine plasma decreases in response to short-time exercise unlike endurance exercise. Blood plasma apelin concentration determined at rest is lower in long-time regularly trained horses than in the ones at the beginning of their training process.

Managing medical emergencies at endurance rides

Endurance riding is a demanding equestrian discipline that has the potential to present attending veterinarians with challenging medical emergencies. An understanding of the conditions likely to be faced and the...

The Effect of a 160-Kilometer Competitive Endurance Ride on Inflammatory Marker mRNA Expression in Horses

Previous work to evaluate various risk factors for failure to complete competitive endurance rides has examined clinicopathologic parameters, measurements of inflammation, and speed. Here, inflammatory markers were measured before, during, and after a long-distance, competitive endurance ride to examine the intraride dynamics of inflammatory marker expression and attempt to correlate those findings with whether a horse completed or failed to complete the ride. A total of 77 horses entered into the 2018 Tevis Cup Ride in California were enrolled in the study. Peripheral blood samples for mRNA isolation and gene expression analysis for ALOX5AP, CD14, IL-10, IL-1β, IL-6, IL-8, MMP-1, TLR4, TNFα, and TNFSF13B were collected before, during (55 km and 110 km checkpoints), and after (160 km) the ride. No overall significant differences were found between groups of finishing and nonfinishing horses with regard to inflammatory marker expression. There were, however, time point–specific differences in mRNA expression, and, in some cases, these were group-specific. The overall pattern was a profound, initial increase in expression of inflammatory markers at the 55 km checkpoint. Some markers remained elevated beyond this point, whereas others began to decrease toward preride levels. While this work identified some similarities with previously published works, intraride sampling revealed additional changes in inflammatory marker expression. As such, investigators working with endurance horses should consider the addition of intraride sampling, when possible, to ensure that significant but short-lived changes in mRNA expression are not missed.

Objective Detection and Quantification of Irregular Gait With a Portable Inertial Sensor-Based System in Horses During an Endurance Race—a Preliminary Assessment

Detection of irregular gait (IG) during endurance competitions is based on a brief subjective veterinary examination. Horse elimination due to IG is common and may elicit competitors' complaints. We hypothesized that detection of IG by objectively assessing motion asymmetry can be performed during endurance competitions. The aim of this preliminary study was to start investigating the feasibility of detecting and quantifying IG with a portable inertial sensor-based system (PISBS) during endurance races. Horses participating in two qualifying endurance rides were simultaneously and independently evaluated by Fédération Equestre Internationale veterinarians and the PISBS, and the results were compared after the rides. Asymmetric vertical displacement of the head and/or pelvis measured with the PISBS indicated severity of IG and identified the affected limb(s). Veterinarians and competitors answered questionnaires about the use of the PISBS. The PISBS detected IG in 21/22 horses (48/70 evaluations). Significant disagreement between the PISBS and veterinarians was detected. Disagreement between the PISBS and veterinarians was no longer detected after reducing the sensitivity of the PISBS by reclassifying horses with mild IG as sound. Competitors and veterinarians had favorable impressions about the use of the PISBS but recommended reducing instrumentation time and trotting distance for expediency. Inherent human limitations can explain the lower sensitivity of veterinary evaluation relative to PISBS evaluation. Simple methodological changes are likely to address the issues raised in this study by competitors and Fédération Equestre Internationale veterinarians. Additional studies are needed to complete the feasibility assessment of objective detection and quantification of IG during endurance competitions with a PISBS.

Fédération Equestre Internationale endurance events: Risk factors for failure to qualify outcomes at the level of the horse, ride and rider (2010–2015)

An epidemiological study of elite endurance riding was conducted using data from every Fédération Equestre Internationale (FEI) endurance event from 2010 to 2015, comprising 82,917 starts. The aim of the study was to identify risk factors associated with failure to qualify outcomes for horses during FEI endurance rides. The FEI endurance rules state that, during a ride, horses must be assessed by veterinarians several times, giving veterinarians the opportunity to prevent those horses exhibiting signs of lameness or metabolic problems from continuing further. Multivariable logistic regression models were constructed to identify horse, ride and rider level risk factors associated with failure to qualify. Risk factors particularly associated with increased likelihood of failure to qualify due to lameness included age of horse≥9 years, male horse, male rider, field size≥61 horses and if the ride was held in region group II (Northern and Eastern Europe). Factors associated with increased likelihood of failure to qualify due to metabolic problems included whether the ride was held in region group VII (North Africa and the Middle East), ride distance≥100km and male rider. Some risk factors, such as field size, may be modifiable at the ride level. Other risk factors such as horse age or sex are unmodifiable, but awareness of the risk contributed by these factors can provide veterinarians with additional information while treating horses during endurance rides.

Veterinary problems of endurance horses in England and Wales

Several studies have shown that a considerable proportion of horses are eliminated from endurance rides due to lameness and metabolic problems. Limited information is available on specific veterinary issues in endurance horses and there are no descriptive data on veterinary problems in a large population of endurance horses. The aim of this study was to describe veterinary problems occurring in endurance horses in England and Wales, the regions of the United Kingdom where endurance rides are organised and regulated by Endurance Great Britain (Endurance GB). A comprehensive online self-completed questionnaire was used for data collection (30th December 2015-29th February 2016) All members of Endurance GB who were the main rider of one or more endurance horses were eligible to participate. From the target population of 1209 horses, 190 questionnaires were completed by riders, resulting in a 15.7% response rate. The most common rider-reported veterinary problem was lameness, affecting 152/190 (80.0%) of endurance horses at some point during their careers and 101/190 (53.2%) of horses in the previous 12 months. Detailed information on the most recent episode of lameness was available for 147 horses. Seventy-six percent of these lameness episodes (112/147) had been initially identified by a veterinarian, but only 52% of these lameness episodes were investigated further by a veterinarian, despite the high proportion of horses affected by lameness and the proportion of horses with recurrent lameness episodes. The second most common veterinary problem was thoracolumbar region pain, followed by non-specific cough, skin disease and colic. Education of endurance riders may improve the number, quality and timing of veterinary investigations, especially for lameness and thoracolumbar region pain.

Cross-Sectional Survey of the Management and Training Practices of Endurance Horses in New Zealand: A Pilot Study

The aim of the study was to conduct a cross-sectional survey of a cohort of national and Fédération Equestre Internationale (FEI) level riders to provide an overview of the management and training practices of endurance horses in New Zealand. Data were collected from a convenience sample of 53 riders participating at four endurance rides (including a 3* FEI event). The questions covered demographics of the rider and horse as well as general management and training practices. Before the first competitive ride of the season, horses were ridden a median of five (interquartile range [IQR], 4–6) days a week and were in training for a median of eight weeks (IQR, 6–9). The first competitive ride of the season marked the transition from long slow distance work to more competition-specific work. Increases in training were associated with a reduction in distance, an increase in speed, and no change in frequency. Conditioning often incorporated farm work, hill work, and hacking. After a competitive ride, just over half (57%; 24/42) of respondents gave their horses 1 day off for every 10 km ridden in the ride. Most respondents (81%; 42/52) reported key milestones for their horses during training; heart rate and Global Positioning System (GPS) monitors were used by 61% (31/51) and 63% (31/49) of respondents, respectively. This pilot study highlighted that many riders collected heart rate and GPS data, suggesting there is scope for further detailed studies to gain more accurate training data on endurance horses in New Zealand.

The Effect of Different Physical Exercise on Plasma Leptin, Cortisol, and Some Energetic Parameters Concentrations in Purebred Arabian Horses

Leptin is a hormone that coordinates food intake, energy expenditure, and metabolic rate; it is, however, unknown how exercise influences plasma leptin concentration in horses. The aim of the study was to evaluate the exercise-induced changes in plasma leptin concentration in purebred Arabian horses competing in races and endurance rides. A total number of 26 horses (12 purebred Arabian racehorses aged 3–5 years and 14 endurance horses aged 7–14 years) were studied during performing routine physical exercise. From each horse, blood samples were collected at rest and immediately after the exercise session. Concentrations of plasma leptin, cortisol, lactic acid, uric acid, triacylglycerols, glycerol and free fatty acids were determined. Exercise-induced increase in cortisol and free fatty acid values were higher in endurance horses than in racehorses. Neither endurance nor race exercises influenced the plasma leptin concentration. Further research is needed to elucidate the effects of different types of exercise on leptin synthesis and secretion in horses.

Changes in Movement Symmetry During Long‐Term Exercise in Horses

IntroductionAsymmetry of the trot may occur or increase during endurance rides due to lameness, pain or fatigue. By visual inspection of the movement it is difficult for veterinarians, riders and researchers to distinguish between fatigue and low‐grade lameness, which make objective movement analysis relevant for this purpose. The aim of this study was to determine changes in movement symmetry during long‐term exercise.MethodsMovement symmetry of 45 horses finishing endurance rides of 120–160 kilometres was determined by tri‐axial accelerometry according to an earlier published method. Data was collected in Denmark and Germany from 5 international competitions between 2011 and 2013. Movement was assessed at trot on a straight‐line in‐hand on the day before the race and 30 mins to 3 hrs after passing the final veterinary examination. An overall symmetry index S was calculated on the basis of trunk accelerations measured at 240 Hz during 8 strides. All trotting sequences were recorded on videotape. A paired t‐test was performed comparing symmetry indices before and after racing for each individual horse.ResultsA significant decrease in post‐ride symmetry was detected (P = 0.0042). This is seen as a lower S‐index before racing (‐6.18; SD = 0.86. CI [‐6.427; −5.923]) compared to after racing (‐5.67; SD = 0.79; CI [‐5.908; −5.434]).ConclusionsThis study indicates that the biomechanical method applied allows quantification of the symmetry of movement during field conditions. Most horses had decreased movement symmetry after the race. Accordingly the study provides the basis for further investigation of the causes, including surface, climate and fitness; and the possible health consequences of asymmetric movement developed during long‐term exercise.Ethical Animal ResearchThe study was pre‐approved by the FEI, the local organizing committees, ground jury, and Danish riding association (DRF). Participation was voluntary and the owner or rider signed an informed consent. All information regarding the horses is kept confidential and the horses coded for anonymity. Sources of funding: This study is part of a university and government funded PhD project. Private funding from “Hesteafgiftsfonden” and KDH (Royal Danish Horse Insurance). Competing interests: none.

Fatalities Associated with American Endurance Ride Conference Sanctioned Endurance Rides (2002–2013)

IntroductionFatalities are recognized as a consequence of prolonged endurance exercise but data documenting incidence and causes is limited.MethodsNumbers of horse starts and fatalities were obtained from the American Endurance Ride Conference (AERC) website (www.aerc.org) and further details about fatalities were obtained from horse owners and attending veterinarians. Annual incidence rates were calculated and odds ratios for region and ride length were determined.ResultsFrom 2002–2013 there were 252,738 horse starts in AERC sanctioned rides and 67 fatalities attributable to the demands of endurance exercise were documented. 46/67 horses were eliminated while 21 successfully completed the ride and were deemed fit to continue. Thirteen horses died while euthanasia was performed in the remaining 54 instances, and 51% had necropsy examinations performed. 81% of the fatalities developed acute abdominal pain and necropsy findings included gastric rupture in 12%. Fatalities were also related to financial constraints as 28% of riders declined fluid therapy, referral to surgical facilities, and/or surgery when recommended. Horses competing in the Central and Midwest regions appeared at lesser risk, while those in the Southwest and Northeast regions appeared at greater risk, but low numbers of fatalities precluded reaching statistical significance. In contrast, the risk of fatality was 2 (1 fatality per 3,711 starts) and 12 (1 fatality per 648 starts) times more likely for participation in 80 and 160 km rides, as compared to competition in Limited Distance (40 to 56 km) rides (1 fatality per 8,057 starts).ConclusionsOverall fatality rates were low; however, risk increased with ride distance. Acute abdominal pain was the most common clinical presentation.Ethical Animal ResearchThis retrospective study used data available on the American Endurance Ride Conference (AERC) website and additional documents provided by the AERC. Sources of funding: none. Competing interests: Dr. Balch is a member of AERC Veterinary Committee, Research Committee, and Board of Directors and Dr. Schott is a member of the AERC Research Committee.

Heart Rate Recovery Time in Exercise Testing of Endurance Horses

IntroductionEndurance horses must attain heart rates below a certain limit (usually 64 beats/min) to pass veterinary inspections in endurance rides. The time necessary for heart rate recovery is therefore important in this equestrian discipline. The objective was to determine heart rate (HR) and heart rate recovery time (HRtime) of endurance horses exercised at various velocities.MethodsTwelve Arabian endurance horses completed an incremental field exercise test with concurrent ECG‐recording. Horses were actively competing at distances of 80–160 km. The exercise protocol defined five intervals with intended velocity range of 11–13 km/h, 15–17 km/h, 18–20 km/h, 21–25 km/h, and &gt;25 km/h, respectively. Each interval was terminated by a halt lasting until HR declined to 64 beats/min. Velocity was determined by a global positioning system, while HR and HRtime were calculated from the ECG. Descriptive statistics was performed.ResultsVelocity, HR and HRtime (as mean ± SD); Interval 1: 12.4 ± 0.9 km/h, 104 ± 11 beats/min, 50 ± 34 s; Interval 2: 15.9 ± 0.5 km/h, 120 ± 9 beats/min, 128 ± 81 s; Interval 3: 20.0 ± 0.6 km/h, 133 ± 10 beats/min, 202 ± 120 s; Interval 4: 22.9 ± 1.0 km/h, 140 ± 11 beats/min, 264 ± 170 s; and Interval 5: 29.3 ± 3.8 km/h, 171 ± 15 beats/min, 341 ± 187 s. HR showed linear correlation with velocity. HRtime varied between horses especially after greater velocities, with a tendency of being shortest in the best performing horses. Four outliers of HRtime were excluded from horses reluctant to stand still during the halt due to anticipatory excitement.ConclusionsHeart rate recovery time shows great individuality and could potentially be used as a performance indicator in endurance horses. Possible fluctuations of HR due to anticipatory excitement during the halt may prolong HRtime and must be accounted for.Ethical Animal ResearchExplicit owner informed consent for participation in this study is not stated. Sources of funding: University of Copenhagen. Competing interests: None.