Endurance Horses Research Articles

Suspected myofibrillar myopathy in Arabian horses with a history of exertional rhabdomyolysis.

Although exertional rhabdomyolysis (ER) is common in Arabian horses, there are no dedicated studies describing histopathological characteristics of muscle from Arabian horses with ER. To prospectively identify distinctive histopathological features of muscle from Arabian endurance horses with a history of ER (pro-ER) and to retrospectively determine their prevalence in archived samples from Arabian horses with exertional myopathies (retro-ER). Prospective and retrospective histopathological description. Middle gluteal muscle biopsies obtained from Arabian controls (n=14), pro-ER (n=13) as well as archived retro-ER (n=25) muscle samples previously classified with type 2 polysaccharide storage myopathy (15/25), recurrent exertional rhabdomyolysis (7/25) and no pathology (3/25) were scored for histopathology and immunohistochemical staining of cytoskeletal proteins. Glutaraldehyde-fixed samples (2 pro-ER, one control) were processed for electron microscopy. Pro-ER and retro-ER groups were compared with controls using Mann-Whitney U and Fisher's exact tests. Centrally located myonuclei in mature myofibres were found in significantly more (P<0.05) pro-ER (12/13) and retro-ER (21/25) horses than controls (4/14). Degenerating myofibres were not evident in any biopsies. Retro-ER horses had amylase-resistant polysaccharide (6/25, P<0.05) and higher scores for cytoplasmic glycogen, rimmed vacuoles and rod-like bodies. A few control horses (3/14) and significantly (P<0.05) more pro-ER (12/13) and retro-ER (18/25) horses had disrupted myofibrillar alignment and large desmin and αβ-crystallin positive cytoplasmic aggregates. Prominent Z-disc degeneration and focal myofibrillar disruption with regional accumulation of β-glycogen particles were identified on electron microscopy of the 2 pro-ER samples. In a subset of Arabian horses with intermittent episodes of exertional rhabdomyolysis, ectopic accumulation of cytoskeletal proteins and Z-disc degeneration bear a strong resemblance to a myofibrillar myopathy. While many of these horses were previously diagnosed with type 2 polysaccharide storage myopathy, pools of glycogen forming within disrupted myofibrils appeared to give the false appearance of a glycogen storage disorder.

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.

27 An online survey of feed management and electrolyte use in endurance horses in the United Kingdom

Esophageal obstruction or “choke” is a relatively common occurrence in equines. It often results from improper mastication, consuming feed too quickly, dehydration, or a decrease in saliva production. Esophageal obstruction is a medical emergency during which a horse cannot dislodge a bolus of feed from the esophagus and must wait for human intervention or for the block to be softened and moved by peristalsis. This condition may result in the formation of ulcers, esophageal rupture, aspiration pneumonia, and possibly death. Grazing muzzles have been shown to slow the rate of forage intake. We hypothesized that grazing muzzles could also be used to decrease the rate of pelleted feed intake and so possibly reduce the risk of equine esophageal obstruction in horses fed large meals of pelleted feed. The objective of this research was to compare the rate of pelleted feed intake for horses wearing grazing muzzles to those wearing no muzzle. Using a crossover design, horses were randomly assigned to 3 groups with each horse receiving each treatment. Treatments were as follows: no muzzle, easy breath grazing muzzle, or tough 1 nylon grazing muzzle. Eight adult stock-type horses aged 5 ± 1 years were offered 2.27 kg of pelleted concentrate to consume in a 10-minute period once daily. The study was comprised of 3 periods (5 days each) with a 2-day resting period between each. Horses were weighed daily and no significant change in bodyweight was observed. Data for daily intake were analyzed using the PROC MIXED procedure of SAS with significance established at P < 0.05. Both the easy breath grazing muzzle and the tough 1 nylon grazing muzzle reduced rate of intake (P < 0.05) during a 10-minute feeding interval as compared with no muzzle. The findings of this study revealed that grazing muzzles may be a viable option to reduce the rate of intake of pelleted feed, which may benefit horses susceptible to choke as a result of rapid feed ingestion.

Implementation of field cardio-respiratory measurements to assess energy expenditure in Arabian endurance horses

Measurements of respiratory exchanges in genuine exercise conditions are undoubtedly of interest to further define the energy needs of endurance horses. However, the equine K4b2, the gas exchanges portable device validated for equines, has not been used in Arabian endurance horses yet. Therefore, the objective of this study was to implement field cardio-respiratory measurements in such horses using the equine K4b2 in order to assess energy expenditure (EE). Measurements of heart rate (HR), oxygen uptake (VO2), carbon dioxide production (VCO2), respiratory frequency (RF), tidal volume (VT) and minute expired volume (VE) were carried out at rest and during a 20-min submaximal incremental field exercise in five trained Arabian endurance horses equipped with the K4b2 system. The relationship between HR and VO2 was determined for each horse. EE of the exercise session was calculated from direct VO2 measurements and individual HR-VO2 regression. Out of the five horses, four tolerated the equipment. Respiratory and metabolic variables at rest and during exercise, as well as EE measured at the different gaits, were consistent with reported values in exercising horses: VO2 ranged from 4.8 to 54.1 ml/min per kg from rest to canter, respectively, and EE from 82 to 1095 J/min per kg BW. The 20-min exercise session EE accounted for 6258 and 6332 J from direct VO2 measurements and individual HR-VO2 regression, respectively, which did not differ significantly. Providing an adaptation period and several technical adjustments, the present equine K4b2 could be used to assess EE in Arabian endurance horses in a controlled environment. The prediction of EE from the individual VO2–HR relationship might be an alternative method to evaluate EE when VO2 measurements are not possible.

Expression microarray as a tool to identify differentially expressed genes in horses suffering from inflammatory airway disease.

Inflammatory airway disease (IAD) affects performance and well-being of horses. Diagnosis is primarily reached by bronchoalveolar lavage (BAL) cytology which is invasive and requires sedation. The purpose of this study was to identify differential gene expression in peripheral blood of horses with IAD using species-specific expression microarrays. Equine gene expression microarrays were used to investigate global mRNA expression in circulating leukocytes from healthy, IAD-affected, and low-performing Standardbred and endurance horses. Nine genes in Standardbred and 61 genes in endurance horses were significantly differentially regulated (P<.001). These genes were related to inflammation (eg, ALOX15B, PLA2G12B, and PENK), oxidant/antioxidant balance (eg, DUOXA2 and GSTO1-1), and stress (eg, V1aR, GRLF1, Homer-2, and MAOB). All these genes were up-regulated, except down-regulated Homer-2 and MAOB. DUOXA2, ALOX15B, PLA2G12B, MAOB, and GRLF1 expression was further validated by RT-qPCR. An increase in glutathione peroxidase (GPx) activity in heparinized whole blood of IAD-affected Standardbred (P=.0025) and endurance horses (P=.0028) also suggests a deregulation of the oxidant/antioxidant balance. There was good correlation (r=.7354) between BAL neutrophil percentage and whole blood GPx activity in all horses. This study showed that circulating blood cell gene expression reflects inflammatory responses in tissues. Whether any of the genes have potential for diagnostic applications in the future remains to be investigated. Although not specific for IAD, whole blood GPx activity appears to be correlated with BAL neutrophil percentage. This finding should be further assessed by testing a larger number of horses.

Comparison of echocardiographic measurements in elite and nonelite Arabian endurance horses

To determine whether echocardiographic variables differed between successful (elite) and less successful (nonelite) Arabian endurance horses. 34 Arabian horses that competed in endurance racing. Horses were assigned to either an elite or nonelite group on the basis of results of a previous competition, and a standardized echocardiographic examination was performed on each horse within 1 to 4 weeks after that competition. Multivariable logistic regression with backward stepwise elimination was used to create a prediction model for the determination of horse status (elite or nonelite) as a function of the measured echocardiographic variables. The elite and nonelite groups consisted of 23 and 11 horses, respectively. One horse in the nonelite group had a frequent ventricular dysrhythmia that could have negatively affected its performance and rider's safety, whereas none of the horses in the elite group had remarkable cardiac abnormalities. The left ventricular internal diameter during systole and diastole and left ventricular mass and stroke volume were significantly greater for horses in the elite group, compared with those for horses in the nonelite group. The final logistic regression model correctly predicted the horse status for all of the horses in the elite group and 8 of 11 horses in the nonelite group. Results indicated that heart size was significantly associated with performance for Arabian endurance horses in a manner similar to findings for Thoroughbred and Standardbred racehorses in active competition.

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.

Genetic Component of Endurance Ability

IntroductionArabian horses have the best records in long distance endurance racing (80–160 km). The endurance horses are interesting models to calculate the heritability (h2) of exercise ability. Heritability indicates the percentage of trait transmitted by parents to their descendants (h2 = Genetic variance/Total variance). In human athletes, heritability of physiological traits calculated using twin design were 0.12, 0.72 and 0.32 for VO2max, Heart Rate max and endurance capacity respectively. Heritabilities of 0.28 and 0.06 for speed and placing respectively are reported in endurance horses. The aim of this study was to calculate the heritability of recovery heart rate, cardiac recovery time and average speed in long distance endurance racing.MethodsThe results of 132 endurance races (80–160 km) from 2007 to 2011 were analyzed. The database included 4421 horses of known pedigrees representing 655 sires with a mean of 18.5 products per sire. The data were analyzed using Restricted Estimator of Maximal Likelihood (REML, VCE6) method with animal mixed model including country, ride distance, age, gender, common environment as fixed effects and animal genetic as random effect.ResultsHeritabilities (SE) were 0.12 (0.06), 0.15 (0.02) and 0.46 (0.08) for speed, recovery heart rate and cardiac recovery time respectively.ConclusionsThe speed and heart rate recovery seem more influenced by training and environmental effects than the cardiac recovery time which is more influenced by genetics. This high heritability is consistent with heritability of V200 found in French Trotter population previously and may indicate a putative quantitative trait linkage.Ethical Animal ResearchExplicit owner informed consent for participation in this study is not stated. Sources of funding: National Studs (IFCE) and the Arabian Horse Association (ACA). Competing interests: none.

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.

Preliminary Results on CD147 Expression in Red Blood Cells of Arabian Horses

IntroductionDuring anaerobic glycolysis for energy production, lactate and H+ ions accumulate in muscle fibers and pass into the bloodstream. Monocarboxylate transporter type 1 and its ancillary protein CD147 transport H+ and lactate ions from the plasma into red blood cells, thereby maintaining acid/base homeostasis and retarding systemic acidosis and fatigue. The aim of this study was to compare the levels of CD147 protein in the red blood cells of Arabian horses with different levels of athletic ability.MethodsBlood samples were taken from 12 Arabian horses before exercise. The horses were divided into two groups: untrained horses (UH, n = 6) and 160‐km endurance horses (FEI, n = 6). The amount of CD147 in the plasma membranes of their red blood cells was determined by Western blotting analysis using a human‐specific anti‐CD147 antibody previously validated for horses. The medians were compared by Mann‐Whitney Rank Sum test at 5%.ResultsCD147 protein with a molecular mass of approximately 45 kDa was found in the red blood cell membranes of the studied horses. The CD147 expression levels of the two groups were not different (P = 0.065). The observed median values (min–max) were 0.50 (0.37–1.26) and 0.27 (0.09–0.69) arbitrary optical density units for the FEI and UH group respectively.ConclusionsStudies must be performed with more horses to determine if a different level of CD147 expression exists in FEI horses related to their intensive training programs or to the genetic traits of each horse.Ethical Animal ResearchAll procedures were approved by the institutional animal care and use committee of the university (CEUA, Process: 019314/13). Explicit owner informed consent for participation in this study is not stated. Sources of funding: FAPESP ‐ Fundação de Amparo à Pesquisa do Estado de São Paulo. Process: 2012/24193‐0. Competing interests: none.

Energy Expenditure During a 160 km Endurance Race

IntroductionIn endurance racing, horses are required to complete distances of up to 160 km in a single day. To date, the energy expenditure (EE) of such effort has not been quantified. This study aimed to evaluate EE during a 160 km endurance race from heart rate (HR) monitoring.MethodsThree weeks before competing, two endurance horses (H1 and H2) were submitted to a field exercise test to determine their individual VO2‐HR relationship. VO2 and HR were recorded simultaneously at trot (13–14 km/h for 10 min), and at canter (18–19 km/h for 10 min, and 22–23 km/h for 5 min), using the equine K4b2, a portable metabolic measurement system. H1 was then enrolled in Monpazier CEI and H2 in Florac CEI. HR was monitored from 2 minutes before the start to the finishing line of each loop. EE of exercise was calculated from individual VO2‐HR relationship and caloric equivalent of oxygen.ResultsH1 and H2 completed the race at an average speed of 17.02 and 14.46 km/h, respectively. Mean HR was 108 ± 8 and 124 ± 24 and peak HR was 169 and 204 for H1 and H2, respectively. The proportion of time spent at HR≥180 was 0 and 2.7% for H1 and H2 respectively. EE of exercise was evaluated at 177 and 240 MJ for H1 and H2 respectively.ConclusionsA 160‐km endurance race might present a considerable energy cost, at least 5 times the EE of non‐working state.Ethical Animal ResearchThe project was conducted under license from the Department of Health and Animal Care of the French Veterinary Authority (no. A21002) and ethics committee approval n° B0710. Sources of funding: Burgundy Region and AgroSup Dijon. Competing interests: none.

Innate Variability in Voluntary Drinking in Arabian Horses during Endurance Exercise

IntroductionHuman athletes have been characterized as either ‘good drinkers’ or ‘poor drinkers’ on the basis of voluntary water intake during and after endurance exercise. Similarly, riders of endurance horses have described some horses to be better drinkers than others; however, there are no data in horses to substantiate these claims.MethodsVoluntary fluid intake (FI) by twenty four 2‐year‐old Arabian horses that performed 45–60 km of treadmill exercise in four experiments was recorded. All horses were raised similarly and had no training except a 12 week conditioning period before each experiment. Mean FI intake (each horse performed three or four exercise tests in each experiment) was subjected to cluster analysis to separate horses into poor, average, and excellent drinking groups. FI was also correlated to body weight (BW) loss at the end of the exercise test.ResultsCluster analysis separated horses into poor drinkers (n = 10, FI 8.7 ± 0.7 liters and BW loss of 2.2 ± 0.4%); average drinkers (n = 11, FI 14.1 ± 0.6 liters and BW loss of 1.8 ± 0.2%); and excellent drinkers (n = 3, FI 24.9 ± 0.2 liters and BW loss of 0.7 ± 0.3%). FI was inversely correlated with BW loss (R values between −0.53 and −0.87 for all four experiments, P&lt;0.01).ConclusionsThese data, in groups of young, similarly trained horses, are the first to support that there are innate differences in voluntary drinking during and after endurance exercise in this species.Ethical Animal ResearchAll procedures were approved by the Animal Use Committee of Michigan State University Sources of funding: Equine Health Research Fund of the American Horse Shows Association, WALTHAM Centre for Pet Nutrition, and the Department of Large Animal Clinical Sciences, Michigan State University. Competing interests: none.

Real‐Time Monitoring of the Core Body Temperature of Endurance Horses During Field Exercise

IntroductionContinuous monitoring of core body temperature may provide useful information about the thermal response to metabolic heat load and environmental challenges. The aim of this study was to evaluate a telemetric gastrointestinal (GI) pill (Equivital®) measuring gastrointestinal temperature (GT) during endurance exercise. It was hypothesised that a temperature and metabolic heat profile could be established.MethodsThe GI pill was administered to 6 horses by nasogastric tube (n = 3) or modified‐drench gun (n = 3), the day before competition. During competition, GT, skin temperature and heart rate (HR) were recorded (by Equivital® belt). Other data collected included body weight and rectal temperature (RT), GPS/HR monitor information, and environmental conditions using a data logger. Metabolic heat production was calculated [1] and GT correlations were explored using simple correlation estimates (P&lt;0.05).ResultsData were collected from 6 horses during 80 km (n = 4 horses) and 100 km (n = 2) competition days with mean data loss of 7.4% (±2.4%). GT profiles showed increasing temperature with cumulative metabolic heat production, and time to reach maximum GT was 2.14–6.29 h (maximum GT range: 38.4–39.5°C). During exercise (7 h 6 min ± 1 h 3 min duration), mean and maximum speeds ranged from 10.1–14.5 km/h and 23.5–30.8 km/h, respectively. No correlation was found between GT and HR, skin, or environment temperature. Maximum GT increased with bodyweight (r = 0.775, P = 0.08). GT was systematically higher than RT (mean difference +0.46°C).ConclusionsGT was recorded successfully during competition with minimal data loss. The GI pill has great potential as a method to further investigate thermoregulation in horses under field conditions.Ethical Animal ResearchAll studies were performed under the Adelaide Animal Ethics Committee, University of Adelaide. Explicit owner informed consent for participation in this study is not stated. Sources of funding: The equipment for the project was funded by the Faculty of Science ‘Grant for minor equipment’, University of Adelaide, Australia. Competing interests: none.

Serum Immunoglobulin Concentrations in Racing Endurance Horses

IntroductionSerum immunoglobulin fractions were evaluated in horses participating in multi‐day endurance exercise.MethodsSerum IgGa, IgGb, IgG(T), IgA, and IgM were measured using horse‐specific ELISA kits in 44 trained horses prior to racing, after each day of racing 50 miles per day and in 15 untrained matched control horses. Data were analyzed via repeated measures ANOVA (P&lt;0.05).Results44, 18 and 9 horses completed one, two and three days of racing, respectively. Serum IgA before racing (1.97 ± 0.14 mg/dL) was similar to controls (1.48 ± 0.19) and after one, two or three days of racing (1.98 ± 0.13, 1.80 ± 0.15 and 1.76 ± 0.26). Serum IgM before racing (1.02 ± 0.05 mg/dL) was similar to controls (1.08 ± 0.12) and after one, two or three days of racing (1.03 ± 0.06, 0.91 ± 0.08 and 0.89 ± 0.11). Serum IgG(T) before racing (6.10 ± 0.41 mg/dL) was similar to controls (6.29 ± 0.58) and after racing one, two or three days (6.23 ± 0.45, 6.62 ± 0.63, and 6.65 ± 1.34). Serum IgGa was 2.41 ± 0.10 mg/dL before racing, and was similar to controls (2.45 ± 0.22) and each day of racing (2.58 ± 0.14, 2.39 ± 0.20, and 2.61 ± 0.22, on days one, two and three of racing). Resting serum IgGb concentration was significantly lower in control (5.71 ± 0.54 mg/dL) than trained horses (7.65 ± 0.41).ConclusionsSerum IgGb is higher in trained endurance horses, perhaps reflecting immune stimulation related to disease exposure or more frequent vaccination.Ethical Animal ResearchAll procedures were approved by the Oregon State University Institutional Animal Care and Use Committee. Owner informed consent was obtained for all horses in the study. Sources of funding: Department of Biomedical Sciences at Oregon State University. Competing interests: none.

Standardized Exercise Test in Young Endurance Horses

IntroductionThe objective of this study was to validate a field standardized exercise test (SET) adapted for young endurance horses and to evaluate the effects of age/conditioning level on speed and heart rate values.MethodsThe study involved 31 horses of Arabian origin bred specifically for endurance and aged 4 yo (n = 11), 5 yo (n = 13) or 6 yo (n = 7). The SET consisted of a warm‐up, followed by 15 (4 yo), 30 (5 yo) or 45 (6 yo) minutes of canter at a comfortable steady speed, and finished with 500 meters of fast gallop. Heart rate (HR) was recorded continuously during the SET. The velocities at which HR reached 160 and 200 beats per minute (V160 and V200) were calculated by the linear regression of HR versus speed.ResultsAll horses were able to complete the SET. Resting HR was higher in 4 y than in 5 y and 6 y (P&lt;0.05 via Student's t test). HR and velocities during the SET did not vary significantly with age. Mean ± SD values for 4 yo, 5 yo and 6 yo respectively are as follows: Resting HR: 47.5 ± 7.2, 42.3 ± 3.2, 41.3 ± 5.4 bpm; HRcanter: 162.7 ± 14.3, 156.9 ± 17.3, 161.4 ± 10.7 bpm; Vcanter: 22.6 ± 0.9, 22.4 ± 1.2, 23.3 ± 1.6 km/h; HRsprint: 191.3 ± 18.1, 181.7 ± 18.5, 184.1 ± 16.2 bpm; Vsprint: 30.3 ± 3.0, 31.5 ± 6.4, 35.3 ± 6.9 km/h; V160: 25.8 ± 3.5, 24.8 ± 5.0, 27.1 ± 5.8 km/h; V200: 36.8 ± 6.1, 37.4 ± 7.3, 44.3 ± 10.9 km/h; Post‐exercice lactatemia: 7.4 ± 4.5, 13.5 ± 3.6, 5.6 ± 3.4 mmol/l. These values perfectly fit with those described previously for adult endurance horses.ConclusionsThe proposed field SET involved both aerobic and anaerobic metabolism reproducing the progress of an endurance race. Further studies are being conducted to discriminate if possible the effects of age from those of conditioning.Ethical Animal ResearchThe study was approved by the Ethics Committee for the Alfort Veterinary School and the University of Paris‐Est; Owner informed consent for participation was obtained. Sources of funding: National Studs (IFCE), The Eperon Funds and the Arabian Horse Association (ACA). Competing interests: none.

Evolution of Echocardiographic Dimensions with Age and Training in Young Endurance Horses

IntroductionIncreasing cardiac dimension with endurance training is well known in adult athletes. However, adaptation of the heart to training in growing Arabian type horses is less well documented.MethodsDuring the national finals for young endurance horses, standardized echocardiographic examinations were performed before the races by two experienced examiners. In 2011 left ventricle (LV) was assessed in 74 horses aged 4‐years (18), 5‐years (33) and 6‐years (23). In 2012 left atrial (LA) dimensions and the great heart vessels were measured in 122 horses aged 4‐years (32), 5‐years (40) and 6‐years (50). Data were normally distributed; age groups and gender were compared by one‐way ANOVA (Holm‐Sidak test for multiple comparisons, significance P&lt;0.05); relationships between echocardiographic dimensions and body weight (BWT) were assessed by linear regressions.ResultsBWT was highest in 5‐year old horses. LV dimensions increased with age, but for most measurements the difference was significant only for the group of 6‐year old horses. The stroke volume (SV) increased (P = 0.0016) and the heart rate decreased (P = 0.06) with increasing age, leading to a constant cardiac output in all age groups. There was a weak relationship between BWT and SV. Two dimensional LA measurements increased between 4 and 5 years but remained constant between 5 and 6 years. LA area measurements and LA functional indices showed no evolution between the groups. Aortic dimension increased with age but pulmonary artery dimension showed no such increase. No influence of gender on echocardiographic dimensions and function could be found.ConclusionsGreat heart vessels, LA and LV dimensions showed different growth patterns between 4 and 6 years of age.Ethical Animal ResearchProcedures were approved by the Ethics Committee for the Alfort Veterinary School and the University of Paris‐Est under number 12/07/11‐1; owner informed consent was obtained. Sources of funding: National Studs (IFCE), The Eperon Funds and the Arabian Horse Association (ACA). Competing interests: none.

Prevalence of exertional rhabdomyolysis in endurance horses in thePacificNorthwesternUnitedStates

Exertional rhabdomyolysis (ER) is a reported syndrome in competing endurance horses; however, the prevalence and cause of ER in this population have not been defined. To determine the prevalence of ER in a sample of endurance racing horses and investigate factors, including relevant genetic defects, contributing to the occurrence of rhabdomyolysis in this group. Prospective clinical study. Riders of 101 horses participating in one of four 50-mile (80.5 km) distance races completed a comprehensive questionnaire regarding the medical history, management and performance of their horse. Serum creatine kinase activity (CK) was measured before and 4 h after completion of exercise. Hair samples were analysed by PCR for the R309H mutation in the glycogen synthase gene (GYS1) responsible for type 1 polysaccharide storage myopathy (PSSM) and the C7360G mutation in the ryanodine receptor 1 (RYR1) gene causing malignant hyperthermia (MH). Samples were obtained from 68 Arabians, 20 half-Arabians and 13 horses of other breeds. Serum CK was above the resting reference interval (145-633 u/l) in 38 horses after racing (median 883 u/l, range 658-3739) but was compatible with values previously reported in apparently healthy endurance horses. Pathological ER was suspected to occur in 4 horses with serum CK activities exceeding 10,000 u/l 4 h after racing (median 84,825 u/l; range 10,846-381,790) including 3 Arabians and one half-Arabian horse. GYS1 and RYR1 mutations were not present in hair samples from any horses. Exertional rhabdomyolysis occurred at a prevalence of 4.0% in a sample of horses participating in 50 mile distance events and all affected horses were Arabian or half-Arabian. The cause of ER in the endurance horse population remains unknown; however, ER in competing Arabian endurance horses is unlikely to be due to type 1 PSSM or MH.

Oxidative profiles of endurance horses racing different distances

Increased oxidative stress during prolonged endurance exercises may result in muscle damage, fatigue and decreased performance. An adequate stress response during training is critical to obtain improved results and high animal welfare standards. The aim of this study was to evaluate the red blood cell haemolysate concentrations of superoxide dismutase (SOD), glutathione peroxidase (GPx), reduced glutathione (GSH) and catalase (CAT) and the plasma concentrations of malondialdehyde (MDA) from endurance horses in different distances at high speed in a tropical climate. Fifteen horses were tested; five at 160km (18.54 - 17.16km/h race speed), five at 120km (21.53 - 17km/h race speed) and five at 80km (20.06 - 18.01km/h race speed). Blood samples were collected at rest, immediately after and three hours after the horses left the final vet check and three, seven and fourteen days after the race. No significant increases (P &gt; 0.05) in the levels of SOD, GPx, GSH, CAT or MDA were observed for any of the times or distances examined. Based on these observations, we conclude that reactive oxygen species (ROS) formation during exercise evokes specific adaptations, such as increased antioxidant/oxidative damage-repairing enzyme activity, increased resistance to oxidative stress and lower levels of oxidative damage.

Protein Catabolism and High Lipid Metabolism Associated with Long-Distance Exercise Are Revealed by Plasma NMR Metabolomics in Endurance Horses

During long distance endurance races, horses undergo high physiological and metabolic stresses. The adaptation processes involve the modulation of the energetic pathways in order to meet the energy demand. The aims were to evaluate the effects of long endurance exercise on the plasma metabolomic profiles and to investigate the relationships with the individual horse performances. The metabolomic profiles of the horses were analyzed using the non–dedicated methodology, NMR spectroscopy and statistical multivariate analysis. The advantage of this method is to investigate several metabolomic pathways at the same time in a single sample. The plasmas were obtained before exercise (BE) and post exercise (PE) from 69 horses competing in three endurance races at national level (130–160 km). Biochemical assays were also performed on the samples taken at PE. The proton NMR spectra were compared using the supervised orthogonal projection on latent structure method according to several factors. Among these factors, the race location was not significant whereas the effect of the race exercise (sample BE vs PE of same horse) was highly discriminating. This result was confirmed by the projection of unpaired samples (only BE or PE sample of different horses). The metabolomic profiles proved that protein, energetic and lipid metabolisms as well as glycoproteins content are highly affected by the long endurance exercise. The BE samples from finisher horses could be discriminated according to the racing speed based on their metabolomic lipid content. The PE samples could be discriminated according to the horse ranking position at the end of the race with lactate as unique correlated metabolite. As a conclusion, the metabolomic profiles of plasmas taken before and after the race provided a better understanding of the high energy demand and protein catabolism pathway that could expose the horses to metabolic disorders.

Effect of physical training on nutrient digestibility and faecal fermentative parameters inStandardbred horses

This study aimed at evaluating, in previously inactive Standardbreds horses, the effect of 5 weeks of an exercise training programme on nutrient digestibility and faecal fermentative parameters (FFPs). As an increase in digestibility had previously been reported in trained endurance horses, we hypothesized that similar results would be found in horses being trained for other types of exercise on a different type of diet. After 3 weeks of dietary adaptation, a digestibility trial (DT1) was undertaken, over 3 days, in eight untrained Standardbreds with a fresh faecal sample being collected on the second day for FFP determinations. Six of the eight horses undertook a training programme, and after 5 weeks of exercise, the DT and the FFP measurements were then repeated (DT2). DT2 began after 3 days of inactivity. The same natural meadow hay (H) and pelleted complementary feed (CF) were fed throughout. For 5 days before the DTs, horses were fed 2.1% BW on a dry matter basis (55:45 ratio H:CF). Body weight and body condition score remained constant. Apparent digestibility of dry matter, organic matter, neutral detergent fibre, hemicellulose, crude protein and gross energy, as well as faecal total volatile fatty acids (VFA), acetate and propionate concentrations were significantly (p < 0.05) higher at DT2 than at DT1. A 5-week exercise programme had a positive impact on nutrient digestibility and FFP. Training may improve dietary energy supply, in particular via increased hindgut VFA production. The potential improvement of digestive efficiency with training should be taken into account when formulating nutritional recommendations for the exercising horse, particularly when performing light work, which is low-intensity exercise for 1-3 h per week.