bluuebunny/crossref_metadata_2025 huggingface dataset:
Physiological measurements and upper and lower respiratory tract evaluation in French Standardbred Trotters during a standardised exercise test on the treadmill
Authors: COUROUCÉ‐MALBLANC A. , PRONOST S. , FORTIER G. , CORDE R. , ROSSIGNOL F.
Published: June 2010

There are a variety of reasons for poor performance in racehorses. Exercise intolerance has often been associated with subclinical respiratory abnormalities, and diagnostic aids are therefore used to enhance clinical detection. Physiological variables can also be measured in order to evaluate the metabolic reponse to exercise. This study evaluated the relationship between physiological measurements and upper airway videoendoscopy during a standardised treadmill exercise test and bronchoalveolar lavage (BAL) cytology in control horses (good racing performance, n = 14) and poor performers (n = 27). The poor performers were divided into 2 groups:Group 1= both upper and lower respiratory airway abnormal findings (n = 10);Group 2= lower respiratory airway abnormal findings (n = 17). Horses inGroup 2were divided into 3 categories:Group 2A= exercise‐induced pulmonary haemorrhage (EIPH; n = 5);Group 2B= small airway inflammation (SAI ± EIPH; n = 7) andGroup 2C= other (n = 5). During exercise, the poor performers had significantly lower arterial Pao2and higher HR and blood lactate concentrations compared to controls. Total nucleated cell count of BAL fluid collected from poor racing performers was significantly higher than in controls; also, epithelial cells and haemosiderophage percentage collected from poor racing performers were significantly higher than in controls. Eight horses with dorsal displacement of the soft palate also had eytological evidence of lower respiratory airway disease. The results of this study suggest that there is a significantly different metabolic response (HR, blood lactate, Pao2) to exercise in poor compared to good performers. As both upper and/or lower respiratory problems can be associated with poor racing performance, a detailed examination of the upper and lower respiratory tracts at rest, during and after exercise is advised.
Airway cooling and mucosal injury during cold weather exercise
Authors: DAVIS M. S. , LOCKARD A. J. , MARLIN D. J. , FREED A. N.
Published: June 2010

In human subjects that exercise strenuously in cold weather, there is evidence that hyperventilation with cold air leads to peripheral airway cooling, desiccation and mucosal injury. Our hypothesis was that hyperventilation with cold air can result in penetration of unconditioned air (air that is not completely warmed and humidified) into the peripheral airways of exercising horses, resulting in peripheral airway mucosal injury. To test this hypothesis, a thermister‐tipped catheter was inserted through the midcervical trachea and advanced into a sublobar bronchus in three horses that cantered on a treadmill at 6.6 m/s while breathing cold (5°C) air. The mean (± s.e.) intra‐airway temperature during cantering was 33.3 ± 0.4°C, a value comparable to the bronchial lumen temperatures measured in man during maximal exercise while breathing subfreezing dry air. In a second experiment, 6 fit Thoroughbred racehorses with satisfactory performance were used to determine whether strenuous exercise in cold conditions can produce airway injury. Horses were assigned to Exercise (E) or Control (C) groups in a random crossover design. Samples of bronchoalveolar lavage fluid (BALF) in the E treatment were recovered within 30 min of galloping exercise in 4°C, 100% relative humidity (E), while in C BALF samples were obtained when the horses had not performed any exercise for at least 48 h prior. Ciliated epithelial cells in BALF were higher in E than in the C treatment. Similar results have been found in human athletes and laboratory animal models of cold weather exercise. These results support the hypothesis that, similar to man, horses that exercise in cold weather experience peripheral airway mucosal injury due to the penetration of unconditioned air.

Furthermore, these results suggest that airway cooling and desiccation may be a factor in airway inflammation commonly found in equine athletes.
Effect of instillation into lung of autologous blood on pulmonary function and tracheobronchial wash cytology
Authors: ART T. , TACK S. , KIRSCHVINCK N. , BUSONI V. , VOTION D. , FREEMAN K. , LEKEUX P.
Published: June 2010

This study aimed at measuring the functional consequences and the pulmonary cytology changes following a simulation of pulmonary haemorrhage. Pulmonary function tests including lobeline‐induced hyperventilation, cytology of tracheo‐bronchial wash (TBW) and thoracic radiographs were performed before, as well as 1, 7, 14 and 28 days after, the instillation of 300 ml of blood into the lungs of 4 horses deemed free of exercise‐induced pulmonary haemorrhage (Group 1). Control data (Group 2) were obtained by instilling the same volume of saline into the lungs of the same horses in a crossover design (control). The instillation of blood or saline resulted in an increase in the number of neutrophils in the TBW. Thoracic radiographs showed increased opacity in the caudodorsal region of the lungs in 4/4 (Day 1) and 2/4 horses (Day 7), inGroup 1, and in 2/4 (Day 1) and 0/4 horses (Day 7) in the control group. These changes were attributed to the instillation procedure rather than the nature of the instilled material. Breathing mechanics and arterial blood gases at rest were not affected in eitherGroups 1or2. However, the maximal expiratory peak flow recorded during lobeline‐induced hyperventilation was significantly lower (P<0.05) and the total pulmonary resistance significantly higher (P<0.05) on Day 1 inGroup 1, but notGroup 2. These observations suggest that expiratory flows might be partly limited in bleeders when breathing at high airflow.
Alveolar fibrosis and changes in equine lung morphometry in response to intrapulmonary blood
Authors: MCKANE S. A. , SLOCOMBE R. F.
Published: June 2010

Necropsy studies of horses suffering exercise‐induced pulmonary haemorrhage (EIPH) have identified mild inflammatory lesions with evidence of alveolar fibrosis and bronchiolitis. These lesions were thought to be the result of viral infections that predisposed the affected regions of the lung to EIPH. We have shown previously that during erythrophagocytosis in the alveolar space, there is a prolonged period of macrophage influx and activation. This present study used morphometric analysis to quantify the effects of macrophage activity during erythrophagocytosis, on the alveolar cell population and physical structure of the alveolar walls. Segments of the bronchial tree were inoculated with either autologous whole blood or serum, at 15, 8, 3 days, 24 h and 30 min prior to euthanasia. Blood inoculation produced many significant changes in the alveolar morphometry including, increased numbers of alveolar macrophages, increased septal thickness, and a markedly increased percentage of collagen in the alveolar walls. Signs of chronic inflammation including increased macrophage activity and erythrophagocytosis coincided with increased alveolar macrophage numbers (10,688 ± 1708 cells/mm3to 30,957 ± 6831 cells/mm3), septal thickness (4.1 ± 0.4 μm to 6.1 ± 0.5 μm) and alveolar septal collagen content (6.6 ± 0.5% to 27.5 ± 3.3%). The results suggest that intrapulmonary blood induces a macrophage dominated inflammatory response, septal thickening and the development of alveolar fibrosis. These changes are the probable cause of the observed alveolar fibrosis and bronchiolitis that was once suspected to be the originating cause of EIPH.
Right ventricular pressure dynamics during exercise: relationship to stress echocardiography
Authors: DURANDO M. M. , REEF V. B. , BIRKS E. K.
Published: June 2010

Thorough evaluation of myocardial function remains difficult to evaluate under exercising conditions. This study described right ventricular (RV) pressure dynamics during and immediately following exercise. Nine Thoroughbreds without evidence of cardiac disease completed treadmill exercise at 110% of the speed necessary to elicit V̇O2maxwhile RV pressures were recorded. RV pressure dynamics were calculated at rest, maximal speed and at 10 s intervals for 2 min after exercise. Stress echocardiography was performed at rest and within 120 s after exercise. Mean dP/dtmax and dP/dtmin values were significantly greater at maximal speed and up to 30 s immediately postexercise than at rest and all time points from 60 to 120 s postexercise. Mean dP/dtmax and dP/dtmin were not significantly different from resting values after 60 s postexercise. Tau (the time constant for ventricular relaxation) decreased significantly with exercise, but was not significantly different from rest at time points from 60 to 120 s following exercise. Mean % fractional shortening (FS) increased postexercise; however, the coefficient of variability was large. Wall motion indices also showed large variability postexercise. These temporal changes in normal horses suggest that exercising RV pressure dynamics may provide a better estimation of cardiac function during exercise than postexercise stress echocardiography.
Relationship between body composition, blood volume and maximal oxygen uptake
Authors: KEARNS C. F. , McKEEVER K. H. , JOHN‐ALDER H. , ABE T. , BRECHUE W. F.
Published: June 2010

It has long been known that body mass and, more specifically, lean body mass are strongly correlated with maximal oxygen uptake (V̇O2max) in man and animals. However, there are no data to date describing this phenomenon in the horse. The purpose of this paper is to examine the relationship between body composition and V̇O2maxin the horse. Twenty‐three healthy and unfit Standardbred mares performed an incremental exercise test (GXT) to measure V̇O2max. Rump fat thickness (RTH), a measure of fat covering, was measured using B‐mode ultrasound. Plasma volume, total blood volume and red cell volume were determined, using the Evan's Blue dye dilution technique and packed cell volume. V̇O2maxwas correlated with body mass (r = 0.541; P<0.01) and exercise haematocrit (exHCT; r = 0.407; P<0.05) but not RTH or the other haematological variables. To eliminate the influence of body mass on the individual variables, a regression analysis was performed on the mass‐residuals of V̇O2max, RTH, plasma volume and exHCT. The residuals of V̇O2maxwere correlated negatively with the residuals of RTH (r = −0.687; P = 0.0003) and positively with the residuals of exHCT (r = 0.422; P = 0.045) but not plasma volume. V̇O2maxcould be predicted from a linear combination of the residuals of RTH and exHCT (r = 0.767; P<0.0001). These data indicate that V̇O2maxin the horse is significantly related to fat‐free mass (FFM), independent of body mass. Red blood cells from the splenic reserve constitute an important factor in the horse's ability to achieve a high V̇O2max. Therefore, lean body mass may be a more appropriate basis for assessing metabolic function in the athletic horse.
Effect of NaCI and NaHCO3on serum ionised calcium and blood gas status during sprinting
Authors: BEARD L. A. , HINCHCLIFF K. W.
Published: June 2010

Sodium bicarbonate is often administered to horses before racing in an attempt to delay fatigue and improve performance. We examined the effect of acid‐base status on serum ionised calcium concentration (iCa) during high intensity exercise in 8 Standardbred mares. In a randomised, blinded, cross‐over study, mares were administered each of 3 treatments, NaCl (0.7 g/kg bwt), NaHCO3(1 g/kg bwt) in 3 l water, or 3 l of water only, 4 h before performing a standardised exercise test to fatigue on a treadmill. Mixed venous blood samples were collected as the horses ran for 5 min at 3 m/s, to fatigue at a predetermined speed (approximately 113% V̇O2max) and for 5 min at 3 m/s. There was no effect of treatment on time to fatigue (P = 0.744). NaHCO3attenuated (P<0.05) the exercise‐induced decrease in venous pH (mean ± s.e. 6.97, 6.95 and 7.06 ± 0.02 at end of sprint for water, NaCl and NaHCO3, respectively). Both serum total calcium concentration (tCa) and iCa increased (P<0.05) with running. NaHCO3decreased iCa (P<0.05) compared to water; iCa of 1.58 and 1.44 ± 0.04 mmol/l before exercise and 1.69 and 1.49 ± 0.05 end sprint, for water and NaHCO3treatments, respectively. These results demonstrate an effect of NaHCO3on iCa during exercise. Further study is necessary to determine the effect of alterations in iCa on exercise performance.
Plasma aldosterone concentration and renal sodium excretion are altered during the first days of training
Authors: MCKEEVER K. H. , SCALI R. , GEISER S. , KEARNS C. F.
Published: June 2010

The purpose of the present study was to determine whether the training‐induced hypervolemic response seen in the horse is associated with aldosterone‐mediated renal mechanisms affecting sodium conservation during the first days of training. Five healthy, Standardbred mares (weight 450–500 kg, age 4–8 years) that were unfit, but accustomed to running on the treadmill, were used to test the hypothesis that repeated submaximal exercise would alter plasma aldosterone (ALDO) concentration and renal excretion of electrolytes in horses within the first 3 days of training. The experiment consisted of a 2 week housing equilibration period followed by a 1 week control period and a 3 day exercise training period (30 min/day at 60% V̇O2max). During control, ALDO and renal fluid and electrolyte losses were measured for 24 h on 3 separate days. Renal function (urine volume [UV], 24 h excretion of Na+, K+and CI‐ [UNA+V, UK+V, UClV], clearance of Na+[CNa+], K+[CK+] and Cl−[CCl‐], creatinine [CCr], osmotic substances [Cosm], and solute‐free water [FWC], and the fractional excretion of Na+, K+and Cl−) and ALDO were measured for an additional 3 consecutive days during the training period. There were no differences (P>0.05) in any variable during the control period. Plasma volume increased (+18.7%, P<0.05) after 3 days of training. During training, there were no significant changes in plasma osmolality, electrolyte concentrations or CCr. Training caused decreases (P<0.05) in UV (‐30%), UNA+V (‐73%), UK+V, (‐55%) and UCl‐V (‐70%). Training also caused decreases (P<0.05) in Cosm(‐30%), through decreases in CNa+(‐60%), CK+(‐60%), and CCl‐(‐66%). Interestingly, FWC increased (+30%, P<0.05), whereas, there were significant decreases in the fractional excretion of Na+(‐59%), K+(‐48%) and Cl−(‐60%). Training caused substantial elevations in both pre‐exercise (967%, P<0.05) and postexercise (+3013%, P<0.05) plasma ALDO concentrations suggesting an increase in both basal levels and the responsiveness to acute exercise. Together, these observations suggest that mechanisms affecting tubular conservation of electrolytes contribute to the early response to training. However, it is also concluded that renal mechanisms appear to be only part of the mechanism for conserving sodium and water intake as well as training‐induced changes in gastrointestinal mechanisms affecting electrolyte and water balance.
Metabolic and osmoregulatory function at low and high (3800 m) altitude
Authors: GREENE H. M. , COGGER E. A. , MILTENBERGER T. L. , KOCH A. K. , BRAY R. E. , WICKLER S. J.
Published: June 2010

Altitude evokes physiological adjustments that include not only respiratory and cardiovascular properties, but also metabolic function, renal and endocrine responses. The purpose of the present study was designed to expand our understanding of the physiological process involved with acclimatisation to high altitude in equids. The study examined temporal effects on metabolic and osmoregulatory function in horses (n = 6) at rest and postexercise at 3800 m. Animals were studied at 225 m (Pb = 743 mmHg) and during a 10 day stay at altitude (Pb = 487 mmHg). Rest samples were taken 90 min postprandial at 0830 h and immediately after the gallop phase of a standard exercise test. Changes in glucose, insulin, cortisol, thyroxine, sodium, potassium, chloride and total protein were assessed at both altitudes. Exercise stimulated increases in cortisol, thyroxine, potassium, and chloride; while the concentrations of glucose, insulin, sodium and total protein (regardless of altitude) decreased. Acute (Day 2) altitude exposure (following transport stress) produced significant increases in glucose, cortisol, thyroxine, chloride and protein at rest and exercise. All variables (except cortisol) appeared to stabilise by Day 4 of altitude exposure.

Observations from these data (coupled with haematological and blood gases data) indicate that equids acutely acclimate within 2–3 days to this altitude.
Evaluation of the i‐STAT hand‐held chemical analyser during treadmill and endurance exercise
Authors: SILVERMAN S. C. , BIRKS E. K.
Published: June 2010

This study examined the accuracy and precision of a ***hand‐held, chemical analyser, i‐STAT, in measuring selected blood constituents which may be of use in the diagnosis and management of metabolic disorders found in exercising horses. Venous blood samples were taken from 3 Thoroughbred geldings, fit and trained to exercise on a treadmill, both before and after exercise at a speed sufficient to elicit V̇O2max. The samples were analysed both with the i‐STAT and with in‐house analysers to compare the values of pH, partial pressure of oxygen (PO2), partial pressure of carbon dioxide (PCO2), bicarbonate (HCO3), lactate and base excess (BE). The i‐STAT demonstrated acceptable accuracy and precision for determination of pH, PO2and PCO2, and lactate. We concluded that these parameters could be reliably evaluated by the i‐STAT.

The i‐STAT was further evaluated at veterinary checkpoints during a 60 and 100 mile endurance ride. Because a built‐in thermostat prevents function when the temperature of the analyser is outside the optimum range (16–30°C), it was necessary to insulate the i‐STAT from extreme ambient temperatures. As this portion of the study was conducted in warm temperatures, the appropriate insulation was to maintain the i‐STAT in an ice‐cooled container except during actual blood analyses. Further investigation into the feasibility of using hand‐held chemical analysers at the veterinary checkpoints during endurance rides is recommended.
Carbonic anhydrase activity and sweat gland morphology in trained and untrained Standardbred trotters
Authors: LARSDOTTER S. , HOLM L. , DAHLBORN K. , JANSSON A. , JOSEFSSON M. , RIDDERSTRÅLE Y.
Published: June 2010

Sweat gland morphology and carbonic anhydrase (CA) distribution was studied after exercise in trained and untrained horses using a histochemical technique and light microscopic image analysis. Three trained and 3 untrained Standardbred trotters performed an exercise test (20 min trot at 6 m/s with 5 min walk at 1.8 m/s in the beginning and end) on a high‐speed treadmill at 35°C. Skin biopsies were taken before exercise and after trot. The fluid loss after exercise was 10, 12 and 12 g/kg bwt in the untrained horses and 4, 6 and 11 g/kg in the trained. Trained horses had a larger cell area than untrained after exercise, which might be related to an increase in secretory capacity. The area of the cell occupied by CA was independent of training status, but increased with exercise in both groups. The CA activity was higher in untrained animals and increased after exercise in both groups. The change in CA during exercise might be a response to an increasing demand for HCO3‐ secretion during sweat formation. Therefore, the sweat gland undergoes morphological changes due to stimuli such as heat, exercise and training, but species differences are evident. To our knowledge, no one has previously studied the influence of training on the morphology of the equine sweat gland.
Age‐related changes and inheritance of lactate transport activity in red blood cells
Authors: VÄIHKÖNEN L. K. , OJALA M. , PÖSÖ A.R.
Published: June 2010

In red blood cell membranes, the activity of the main lactate carrier, H+‐monocarboxylate co‐transporter (MCT), varies interindividually and its distribution is bimodal. To show the repeatability of MCT activity, 2 to 5 blood samples were taken, at an interval of approximately 1 year, from 51 Standardbred horses, age 2 weeks‐8 years, for a total of 128 observations. The horses could be divided into low (LT) and high (HT) lactate transport activity groups. Age significantly affected (P<0.05) MCT activity such that activity was highest in foals, reached a nadir at 2–3 years, and tended to increase again thereafter. Interindividual variation was not sufficiently high to allow a horse to switch from the LT‐group to the HT‐group, orvice versa.When MCT activity from 4 sires, 15 dams and their 52 offspring was analysed, the data showed that MCT activity is heritable and supported the hypothesis that low MCT activity was caused by a recessive allele in a single autosomal locus. Because MCT activity affects RBC lactate concentrations, the phenomenon may be physiologically significant.
Effects of oral electrolyte supplementation on endurance horses competing in 80 km rides
Authors: SAMPIERI F. , SCHOTT H. C. , HINCHCLIFF K. W. , GEOR R. J. , JOSE‐CUNILLERAS E.
Published: June 2010

Reasons for performing study:There is no evidence that use of oral electrolyte pastes enhances performance in competing endurance horses.

Objective:To ascertain whether oral administration of a high dose (HD) of sodium chloride (NaCl) and potassium chloride (KCl) to endurance horses would differentially increase water intake, attenuate bodyweight (bwt) loss and improve performance when compared to a low dose (LD).

Methods:A randomised, blinded, crossover study was conducted on 8 horses participating in two 80 km rides (same course, 28 days apart). Thirty minutes before and at 40 km of the first ride 4, horses received orally 0.2 g NaCl/kg bwt and 0.07 g KCl/kg bwt. The other 4 received 0.07 g NaCl/kg bwt and 0.02 g KCl/kg bwt. Horses received the alternate treatment in the second ride. Data were analysed with 2‐way ANOVA for repeated measures (P<0.05).

Results:Estimated water intake was significantly greater with HD both at the 40 km mark and as total water intake; however, differences in bwt loss and speed between HD and LD were not found. Treatment significantly affected serum Na+, Cl−, HCO3, pH and water intake, but not serum K+or bwt. Serum Na+and Cl−were significantly higher at 80 km when horses received HD, but no differences were found in early recovery. Venous HCO3and pH were significantly lower throughout the ride and in early recovery when horses received HD.

Conclusions and potential relevance:Other than enhancing water intake, supplementing endurance horses with high doses of NaCl and KCl did not provide any detectable competitive advantage in 80 km rides. Further, the elevated serum electrolyte concentrations induced with HD might not be appropriate for endurance horses.
Endurance exercise is associated with increased plasma cardiac troponin I in horses
Authors: HOLBROOK T. C. , BIRKS E. K. , SLEEPER M. M. , DURANDO M.
Published: June 2010

Reason for performing study: Information is lacking regarding the influence of long distance exercise on the systemic concentration of cardiac troponin I (cTnl) in horses.

Objectives: To determine if the concentration of cTnl in horses competing in 80 and 160 km endurance races increases with exercise duration and if cTnl concentrations can be correlated with performance data.

Methods: Blood samples for the measurement of cTnl and 3 min electrocardiogram recordings were obtained from horses prior to, during and after completion of 80 and 160 km endurance races at 3 ride sites during the 2004 and 2005 American Endurance Ride Conference competition seasons.

Results: Full data sets were obtained from 100 of the 118 horses. Endurance exercise was associated with a significant increase in cTnl over baseline in both distance groups. Failure to finish competition (poor performance) was also associated with an increased cTnl concentration over baseline at the time of elimination when data from both distances were combined. Other than one horse that developed paroxysmal atrial fibrillation, no arrhythmias were noted on the 3 minute ECG recordings that were obtained after endurance exercise in either distance group.

Conclusions: Systemic concentrations of cTnl increase in endurance horses competing in both 80 and 160 km distances. Although final cTnl concentrations were significantly increased over their baseline values in horses that failed to finish competition, the degree of increase was not greater than the increase over baseline seen in the horses that successfully completed competition. The clinical significance of increased cTnl in exercising horses could not be ascertained from the results of this study.

Potential relevance: These data indicate that cardiac stress may occur in horses associated with endurance exercise. Future studies utilising echocardiograpy to assess cardiac function in horses with increased cTnl are warranted.
Thyroid hormone responses to endurance exercise
Authors: GRAVES E. A. , II H. C. SCHOTT , MARTENIUK J. V. , REFSAL K. R. , NACHREINER R. F.
Published: June 2010

Reasons for performing study:Limited information exists about changes in circulating thyroid hormone concentrations during prolonged endurance exercise in horses.

Objective:To examine the effects of prolonged exercise on serum iodothyronine concentrations in horses performing endurance exercise of varying distances.

Methods:Serum concentrations of iodothyronines were measured in horses before and after completion of 40, 56, 80 and 160 km endurance rides (Study 1); daily during a 5 day, 424 km endurance ride (Study 2); and before and for 72 h after completion of a treadmill exercise test simulating a 60 km endurance ride (Study 3).

Results:In Study 1, 40 and 56 km of endurance exercise had little effect on serum iodothyronine concentrations with the exception of a 10% decrease (P<0.05) in free thyroxine (FT4) concentration after the 56 km ride. In contrast, total thyroxine (T4), total triiodothyronine (T3), FT4and free triiodothyronine (FT3) concentrations all decreased (P<0.05) after successful completion of 80 and 160 km rides, with decreases ranging from 13–31% and 47–54% for distances of 80 and 160 km, respectively. Further, pre‐ride T4concentration was lower (P<0.05) and FT3concentration was higher (P<0.05) in horses competing 160 km as compared to horses competing over shorter distances. In Study 2, serum concentrations of T4, T3and reverse triiodothyronine (rT3) progressively decreased (P<0.05) over the course of the multi‐day ride. In Study 3, the greatest decrease (P<0.05) in all iodothyronines was observed at 12 h of recovery, ranging from 25% for FT4to 53% for FT3, but all thyroid hormone concentrations had returned to the pre‐exercise values by 24 h of recovery.

Conclusion:Endurance exercise results in transient decreases in serum iodothyronine concentrations.

Potential relevance:These data are important to consider when thyroid gland function is assessed by measurement of serum iodothyronine concentrations in endurance horses.
Gene expression profiling in blood cells of endurance horses completing competition or disqualified due to metabolic disorder
Authors: BARREY E. , MUCHER E. , ROBERT C. , AMIOT F. , GIDROL X.
Published: June 2010

Reasons for performing study:Genomics using cDNA microarrays could provide useful information about physiological adaptations and metabolic disorders in endurance horses.

Objectives:In order to show that genes are modulated in leucocytes in relationship with performance and clinical status of the horses, gene expression in leucocytes, haematological and biochemical parameters were compared between successful and disqualified endurance horses.

Methods:Blood samples were collected at rest (T0) and just after a 140–160 km endurance race (T1) in 2 groups of horses: 10 continuing successful (S) and 10 disqualified horses stopped at a vet‐gate for metabolic disorders (D). Total RNA was extracted from the blood cells (leucocytes), checked for purity, amplified and hybridised using mouse cDNA microarrays including 15,264 unique genes. Differential gene expressions were studied by hybridisation of each sample T1 vs. a control sample collected at T0 (pool of 20 sound horses).

Results:Some significant differences were observed in the haematology and biochemistry of the 2 groups (Svs.D). InGroup D, rhadomyolysis was confirmed with CK 13,124 u/***l and AST 1242 u/***l. The list of 726 (including 603 annotated genes) significant genes was filtered according to a high P‐value cut‐off (P<0.00001). Among them, 130 were up‐regulated (expression ratio>1.5) and 288 were down‐regulated (<1/1.5). Analysis of variance revealed 62 genes differentially expressed (P<0.05) inGroups DandS.The expression levels of 28 and 50 genes were significantly correlated (r>0.75) with CK and AST level inGroup D, respectively. The gene ontology classification showed that more genes were up‐regulated inSthan in theD.More genes were down‐regulated in the disqualified horses.

Conclusions:Long exercise induced many significant gene modulations in leucocytes. Some genes were expressed in relationship with the clinical phenotype observed inGroup D:rhabdomyolysis and haemolysis.

Potential relevance:Some of these genes could be candidates to explain poor performance or pathologies. Further association studies with a greater number of genes should be conducted.
Trot asymmetry in relation to physical performance and metabolism in equine endurance rides
Authors: MUÑOZ A. , CUESTA I. , RIBER C. , GATA J. , TRIGO P. , CASTEJÓN F. M.
Published: June 2010

Reason for performing study:Trot is a symmetric gait and asymmetry might appear or increase during endurance rides due to lameness, pain or excessive fatigue.

Hypothesis:To assess whether trot asymmetry increases during endurance competitions, whether it is possible to discriminate between horses with different performance and also its possible relationship with metabolism.

Methods:Fifty‐eight horses were filmed at trot during the lameness examinations in the vet‐gates, before the competition (BCO), and afterphases I(at 29 km),2(at 59 km) and3(at the end of the ride, at 80 km) and stride duration (SD) measured in all 4 limbs. A locomotion symmetry index (LSI) was calculated by comparing SD in the diagonal pairs of limbs. In all the cases, the longer diagonal pair SD was compared to the shorter. Horses were classified as symmetric (SyH) when LSI was lower than mean + 2s.d. and asymmetric (ASyH) when LSI was higher than mean + 2s.d. of the data obtained in BCO. Venous samples were withdrawn in the vet‐gates and PCV, WBC, creatinine, TPP, uric acid, CK, AST, LDH, Na, K and Cl were measured. Horses were divided into different performance groups: successful (SH), lame (LH) and metabolic (MH), and according to ride velocity, the SH group was also divided into faster finishers (FF) and slower finishers (SF).

Results:The percentages of SyH were high (>80%) and very similar between the different performance groups. LSI became more asymmetrical in the vet‐gates, especially in the LH and MH groups. LSI presented negative correlations with the velocities during the rides and in the vet‐gates and CK. The ASyH had higher velocities during the rides and plasma CK and lower velocities during the vet‐gates and plasma uric acid concentrations.

Conclusions:Although trot asymmetry increases during endurance events, LSI calculated comparing SD in the two diagonal pair of limbs did not allow the differentiation of horses with different performance.
Stride parameters and hindlimb length in horses fatigued on a treadmill and at an endurance ride
Authors: WICKLER S. J. , GREENE H. M. , EGAN K. , ASTUDILLO A. , DUTTO D. J. , HOYT D. F.
Published: June 2010

Reason for performing study:The relationship between fatigue and stride and/or muscle stiffness requires further study.

Objective:To measure stride parameters in horses undergoing fatigue associated with running at submaximal speeds both on a treadmill and in an endurance ride.

Hypothesis:Stride frequencies and estimates of hindlimb stiffness would be decreased in fatigued horses.

Methods:Horses were fatigued using 2 paradigms: run to exhaustion at a treadmill (4.5 m/sec, 6% incline) and finishing an 80 km endurance ride. Videos were digitised before and after fatigue and analysed for stride parameters: hind limb length, stride frequency, time of contact, step length, duty factor and stride length.

Results:In fatigued horses, stride durations were 5% longer (P=0.007) resulting in lower stride frequencies (P=0.016) and longer stride lengths (P = 0.006). The time of contacts (tc) for stance phase were not different (P = 0.108) nor was duty factor (tc/stride period, P = 0.457). Step length (speed x tc) and hindlimb lengths were also not different (P=0.104, P=0.8). For endurance horses, stride data for nonfatigued horses were consistent with data extrapolated to 4.5 m/sec from nonfatigued horses on the treadmill. Endurance horses slowed (P = 0.002) during the race from 4.55 to 4.03 m/sec and stride lengths were shorter. Despite a slower speed, other stride parameters were unchanged. Hindlimb length was shorter in fatigued horses.

Conclusion:Horses fatigued on a treadmill and during the natural course of an endurance ride responded differently, biomechanically. On the treadmill, where speed is constrained, stride frequencies decreased and stride lengths increased. During one endurance ride, stride frequencies were the same, although speeds were substantially reduced. Limb length was shorter in fatigued endurance horses. It remains to be determined if these changes in mechanics are advantageous or disadvantageous in terms of energetics or injury. Further examination of endurance rides is also warranted.
Measurements of fitness in Thoroughbred racehorses using field studies of heart rate and velocity with a global positioning system
Authors: VERMEULEN A. D. , EVANS D. L.
Published: June 2010

Reasons for performing study:Field based studies of changes in fitness are difficult to conduct in galloping Thoroughbreds. Measurements of heart rate (HR) and real time velocity with a global positioning system (GPS) could provide a method for routine field studies of fitness.

Objective:To investigate measurements of fitness in the field without using multiple, standardised steps of increasing velocity in the exercise test.

Methods:Twelve healthy 3‐ to 5‐year‐old Thoroughbreds were used in the study of reliability, and twelve 2‐year‐old Thoroughbreds in the investigation of the effect of training. Five second averages of velocity and HR were recorded during a typical fast exercise training session, using a GPS and Polar HR monitor. A standardised exercise test protocol was not used. Regression analyses using trot and gallop data were used to calculate velocities at HR of 200 beats/min (V200), and at maximal HR (VHRmax). Data were collected on consecutive ‘fast’ day training sessions to assess the reliability of measurements. The effect of training was investigated with fitness tests in weeks 2 and 6 of ‘fast’ training. Absolute and relative differences were calculated to evaluate reliability, and pairedttests were used to detect an effect of training.

Results:VHRmax, V200and HRmaxwere reliable measurements of fitness, with mean differences of 2% or less. Reliability of VHRmaxwas not dependent on VHRmax. VHRmaxand V200both increased significantly with training (P<0.01), but there was no effect of training on HRmax. There were no significant changes in the slope or intercept of the regression equations after training.

Conclusions:Velocity and HR measurements during field gallop exercise provided reliable measures of fitness which enabled a measurement of the response to training.

Potential relevance:This approach offers a simple, noninvasive method for monitoring adaptations to training in the field.
Racing speeds of Quarter Horses, Thoroughbreds and Arabians
Authors: NIELSEN B. D. , TURNER K. K. , VENTURA B. A. , WOODWARD A. D. , O'CONNOR C. I.
Published: June 2010

Reasons for performing study:While Quarter Horses are recognised as the fastest breed of horse, direct comparisons to race times with other breeds can be misleading. Quarter Horse races begin when the starting gates open. Thoroughbred and Arabian races begin a short distance from the gates after horses have started running. This study compared speeds of these breeds as they accelerate from the starting gates and during the middle and end of races.

Objectives:To compare racing speeds of the 3 breeds, and to compare speeds during various segments of the races.

Methods:Video tapes of races were obtained from a local track. The various race segments were viewed and the winning horse timed by 5 individuals. Fastest and slowest times were removed and the 3 remaining times averaged.

Results:Quarter Horses averaged faster speeds than Thoroughbreds even when Thoroughbreds were raced at a distance (402 m) similar to Quarter Horse races. Both breeds were substantially faster than Arabians. Quarter Horses racing 336 m or less gained speed in each segment of the race while Arabians and Thoroughbreds racing 1006 m ran fastest during the middle of the race and had decreased their speed in the final segment of the race.

Conclusions:Despite similar race times reported for 402 m, Quarter Horses averaged faster speeds than Thoroughbreds when timed from a standing start. In short races, both breeds accelerate throughout the race. Arabians, despite being known for endurance, had slowed by the end of the race.

Potential relevance:This study demonstrates that Quarter Horses achieve faster racing speeds than do other breeds. It also reveals a potential flaw in race‐riding strategy as a more consistent pace throughout the Arabian and longer Thoroughbred races may be more efficient and result in a faster overall race time.
Utilisation of the time constant calculated from heart rate recovery after exercise for evaluation of autonomic activity in horses
Authors: HADA T. , MUKAI H. OHMURA. K. , ETO D. , TAKAHASHI T. , HIRAGA A.
Published: June 2010

Reasons for performing study:Heart rate (HR) recovery immediately after exercise is controlled by autonomic functions and the time constant (T) calculated from HR recovery is thought to be an index of parasympathetic activity in man.

Objectives:To investigate whether it is possible to evaluate autonomic function using the time constant in horses.

Methods:Five Thoroughbred horses were subjected to a standard exercise test. Following pre‐medication with saline, atropine and/or propranolol, the horses ran for 2.5 min at a speed of 8 m/sec at a 10% incline and T was calculated from HR after the exercise. Secondly, 7 Thoroughbred horses were then trained for 11 weeks and T and maximal oxygen uptake (VO2max) measured at intervals of 1 or 2 weeks. In 6 horses, T with atropine pre‐medication was also measured before and after the whole training period. Furthermore, the HR variability at rest was evaluated by power spectral analysis at intervals of 3 or 4 weeks.

Results:Time constant was increased by atropine and/or propranolol pre‐medication, decreased with the progress of training and inversely correlated with VO2maxduring training (r = 0.43, P<0.005). Parasympathetic blockade significantly decreased T only after and not before, the training; however, T was lower in post training than in pre‐training, irrespective of parasympathetic blockade. On the other hand, parasympathetic activity at rest was attenuated and sympathetic activity became predominant following the training.

Conclusion:Heart rate recovery is affected by sympathetic withdrawal and parasympathetic reactivation in horses and suggests that physical training hastened HR recovery by improving the parasympathetic function after exercise with aerobic capacity. However, the effects of other factors need to be considered because the training effect appeared on T even under parasympathetic blockade. The parasympathetic activity at rest is in contrast to that after exercise, suggesting that T does not reflect parasympathetic activity at rest.

Potential relevance:If demonstrated how HR recovery is controlled after exercise, its analysis will be important in the evaluation of physical fitness in horses.
An echocardiographic and auscultation study of right heart responses to training in young National Hunt Thoroughbred horses
Authors: LIGHTFOOT G. , JOSE‐CUNILLERAS E. , ROGERS K. , NEWTON J. R. , YOUNG L.E.
Published: June 2010

Reasons for performing study:There are few data available to determine the effect of training on cardiac valve function.

Objectives:To investigate the effect of commercial race training on right ventricular (RV) and tricuspid valve function in an untrained group of National Hunt Thoroughbreds (TB).

Material and methods:Cardiac auscultation, guided M‐mode echocardiography of the RV, and colour flow Doppler (CFD) tricuspid valve and right atrium were performed in 90 TB horses (age 2–7 years) 1998–2003. Forty horses were examined at least once and 48 horses were examined on at least 2 occasions. Examinations were then classified as: i) before commencement of race training, ii) after cantering exercise had been sustained for a period of 8–12 weeks and iii) at full race fitness. Tricuspid valve regurgitation (TR) murmurs were graded on a 1–6 scale and CFD echocardiography TR signals were graded on a 1–9 scale. Right ventricular internal diameter (RVID) in diastole and systole (RVIDdand RVIDs) was measured by guided M‐mode. Associations between continuous RVID and TR measures and explanatory covariates of weight, age, heart rate, yard and stage of training were examined using general linear mixed models with horse‐level random effects.

Results:On average, RVIDdand RVIDsincreased by 0.08 and 0.1 cm, respectively, per year increase in age (P=0.1 and 0.02) and by 0.3 and 0.4 cm, respectively between pre‐training and race fitness (P = 0.07 and 0.005). Tricuspid regurgitation score by colour flow Doppler increased by 0.6/year with age (P<0.0001) and by 1.8 between pre‐training and race fitness (P< 0.0001). No significant associations were found between any outcomes and weight, heart rate and training yard. Due to the high level of co‐linearity between age and training, multivariable models including both terms were not interpretable.

Conclusions and clinical relevance:Athletic training of horses exerts independent effects on both severity and prevalence of tricuspid valve incompetence. This effect should therefore be taken into account when examinations are performed. Dimensions of RV increase with age and training in TB horses in a manner that appears to be similar to that of the LV.
Effect of light exercise on valvular regurgitation in Standardbred trotters
Authors: BUHL R. , ERSBØLL A. K.
Published: June 2010

Reasons for performing study:Although valvular regurgitation is diagnosed frequently by colour Doppler echocardiography in racehorses at rest, there is currently no information about the effect of exercise on valvular regurgitation.

Objectives:To investigate the effect of light exercise on valvular regurgitation in a population of trotters.

Methods:Standardbred trotters (n = 73) were examined by resting auscultation and echocardiography, of which 50 fullfilled the criteria of the study. Of these, 4 had reduced performance according to the trainers and were not included in the statistical analyses. Horses that showed valvular regurgitations diagnosed by colour Doppler echocardiography at rest, were light exercised and the regurgitant valves were then re‐examined by colour Doppler echocardiography.

Results:Of the 46 horses, 41 (89%) had one or more valvular regurgitations at rest with tricuspid regurgitation present in 83% of horses, mitral regurgitation 46%, pulmonary regurgitation 37% and aortic regurgitation 57%. After exercise, one or more valvular regurgitation persisted for 23 of the 41 horses (56%). The regurgitation decreased significantly for mitral, pulmonary and aortic valves; the mitral regurgitation persisted for 21% of the horses, pulmonary regurgitation persisted for 6% and aortic regurgitation persisted after exercise for 23% with regurgitation diagnosed at rest. Half of those with tricuspid regurgitation at rest still had tricuspid regurgitation after exercise.

Conclusions:The results of this study showed that the majority of small valvular regurgitations disappear after light exercise. However, the severity of tricuspid regurgitation increased in 4 horses. Furthermore, these horses were not performing satisfactorily according to the trainers.

Potential relevance:Studies in man have shown that severity after exercise suggests pathological regurgitation. The present study indicates that echocardiographic examination of valvular regurgitation after exercise might be a relevant examination in horses. However, more studies are needed to evaluate the effect of strenuous exercise on valvular regurgitation in horses.
Right ventricular pressure dynamics and stress echocardiography in pharmacological and exercise stress testing
Authors: DURANDO M. M. , SLACK J. , REEF V. B. , BIRKS E. K.
Published: June 2010

Reasons for performing study:There is interest in using pharmacological stress testing (PST) as a substitute for exercise stress testing (EST) to evaluate cardiac function in horses.

Obectives:To compare the effect of PST and EST on right ventricular pressure dynamics and stress echocardiography.

Methods:Five horses completed a PST and EST in a randomised crossover design. High fidelity pressure transducers were placed in the right ventricle. Continuous pressure signals were digitally collected and stored, and dP/dtmax, dP/dtminand tau calculated from these measurements. ECGs were recorded continuously for 20 h. Echocardiography was performed prior to EST and PST, during and after PST, and immediately post EST. Plasma cardiac troponin I concentrations were measured pre‐ and 3–4 h post stress testing. For PST, 5 μg/kg bwt glycopyrrolate i.v. followed after 10 min by 5 μg/kg bwt/min dobutamine infusion over 10 min was given. EST consisted of a 2 min gallop at 110% speed required to elicit VO2max.

Results:Both EST and PST resulted in a significant increase in right‐ventricular dP/dtmaxand dP/dtminover baseline (P<0.05) and a significant decrease in tau compared with baseline (P<0.05). EST dP/dtmaxand dP/dtminwere significantly greater than PST dP/dtmaxand dP/dtmin(P<0.05) and EST tau was significantly less than PST tau (P<0.05). Two minutes post EST and 5 min post PST dP/dtmaxwere not significantly different, but were significantly less than end‐EST and during PST. Tau was also not significantly different between post EST and post PST, but was significantly decreased end‐EST compared with during PST. FS were not significantly different between PST and post EST, but during PST and post EST all FS were significantly higher than baseline. Cardiac troponin I concentrations were significantly elevated post PST and were greater than post EST. The clinical relevance of this is unknown.

Conclusions:PST had a similar, although less marked effect on the cardiac parameters related to right‐ventricular pressure dynamics and a similar effect on echocardiography as exercise stress testing.

Potential relevance:PST deserves further evaluation in normal horses and those with cardiac disease, and may be complementary to EST to better identify exercise‐induced cardiac dysfunction.