bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison between two post exercise cooling methods
Authors: WILLIAMSON LISA , WHITE S. , MAYKUTH P. , ANDREWS F. , SOMMERDAHL C. , GREEN E.
Published: June 2010

Forty‐two fit 3‐day‐event horses were tested under hot, humid ambient conditions to determine if application of cold water (mean 9°C) over the entire body surface after exercise would cool horses more quickly than regional application of tepid water (mean 31°C); and to determine if topical application of cold water caused myopathy. Horses were exercised under saddle for an average of 81 min. Heart rate data and post exercise plasma lactate concentrations characterised the work effort as low intensity work with short bouts of moderate intensity effort.

Sixteen horses were studied in a crossover design on 2 consecutive days. Immediately after exercise, horses were randomly assigned to the hypercooling protocol (cold water on entire body surface) or the conventional protocol (tepid water on neck, shoulders, torso, underside and legs). Hypercooled horses (Group 1) had significantly lower rectal temperatures at 15, 20, 25 and 30 min after exercise compared to conventionally cooled horses (Group 2). In a supplemental study, an additional 19 horses (Group 3) were hypercooled after exercise. Mean rectal temperatures were significantly decreased from the immediate post exercise rectal temperature at 10, 15, 20 and 25 min after exercise. Based on physical examination and serum AST and CK concentrations, myopathy did not occur in any of the horses. These results suggest that application of cold water to the entire body surface relieves mild to moderate exertional hyperthermia quickly under hot, humid conditions; and that myopathy is not a common complication of this cooling approach.
Adaptation of Thoroughbred horses in training to a fat supplemented diet
Authors: HUGHES S. J. , POTTER G. D. , GREENE L. W. , ODOM T. W. , MURRAY‐GERZIK M.
Published: June 2010

Eight Thoroughbred horses were used in a repeated measures, crossover experiment in which horses were fed a fat supplemented and control diet. On Days 0, 7,14, 21 and 28, horses performed a standardised exercise test (SET) consisting of three 400 m sprints. Digestion trials were performed over 3 days prior to each SET and muscle biopsies were taken pre‐ and post SET. Feeding fat had no negative effect (P>0.05) on digestion of any diet constituent and digestive adaptation to the fat supplemented diet apparently occurred within 1 week. Pre‐exercise muscle glycogen concentrations increased up to Day 14 on both diet treatments. However, when horses were fed the fat supplemented diet pre‐SET muscle glycogen concentration increased until Day 21 (P<0.05) at which time it was higher (P<0.05) than when the horses were fed the control diet. This difference was also present at Day 28. Post SET muscle glycogen concentrations were similar (P>0.05) between treatments on all sampling days. In fat supplemented horses, muscle glycogen utilisation during the SET was increased on both treatments to Day 14 (P<0.05) and increased further to Day 21 when the horses were fed the fat supplemented diet. On Days 21 and 28, glycogen utilisation during the SET was greater (P<0.05) when horses were fed the fat supplemented diet than when fed the control diet.
Effects of post prandial interval and feed type on substrate availability during exercise
Authors: STULL CAROLYN , RODIEK ANNE
Published: June 2010

The glycaemic and lipaemic effects of 3 feeding regimes and 2 post prandial intervals were determined at rest and during exercise using 6 Thoroughbred geldings on 6 testing days according to a Latin square design. Three feeding regimes consisted of a fasting regime and isoenergetic meals (4.1 Mcal) of either cracked corn or alfalfa. One or 4 h after feeding, a standardised exercise test (SET) was imposed on fed and fasted horses. Blood was sampled via jugular catheters every 15 min from 0630 to 1500 h, except during the 55 min SET in which 7 samples were drawn. The SET consisted of three 10 min bouts of saddling, walking to the arena and warm‐up (walking and trotting), followed by 3 bouts of progressively more intense cantering at heart rates of 130–140 (10 min), 150–160 (10 min) and 170–180 (5 min) beats/min. There were no feeding regime effects on pre‐feeding levels of glucose, insulin, lactate, glycerol or free fatty acids (FFA). However, glucose in corn fed horses fell below pre‐feeding concentration during the SET but rebounded at the termination of cantering. Glucose in alfalfa fed and fasted horses gradually rose throughout the SET. Insulin levels closely followed glucose response. During the SET, corn fed horses had higher insulin concentrations (P<0.05) than fasted or alfalfa fed horses. During the onset of the SET one or 4 h post prandially, FFA levels in corn fed horses were less (P<0.05) than in alfalfa fed or fasted horses. Glycerol levels gradually increased during the SET; however, no differences were found between dietary treatments.
Effect of diet on weight and plasma variables in endurance exercised horses
Authors: DANIELSEN KRISTIN , LAWRENCE L. M. , SICILIANO P. , POWELL DEBBIE , THOMPSON K.
Published: June 2010

The purpose of this study was to determine whether a difference in roughage intake could affect electrolyte and water balance in horses during endurance type exercise. In each of 2 experiments, 2 treatments (a high hay or limited hay diet) were assigned in a crossover design so that each horse performed 2 exercise tests, 1 on each treatment. In experiment 1, diet was controlled only the night before the exercise test. Water intake was lower (P<0.001) when horses received the limited hay diet. Exercise caused a decrease in plasma chloride and potassium concentration and an increase in plasma total protein concentration, but there were no diet differences (P>0.05). Weight loss was 2.8% of body weight for both treatments. In experiment 2, horses were adapted to the diets for 7 days prior to the exercise test. Again, water intake was lower when the horses received the limited hay diet (P<0.01). During exercise, both groups lost about 4% of bodyweight, but total protein concentration was lower (P<0.05) in the horses receiving the high hay diet. Plasma potassium concentration initially increased and then decreased during exercise (P<0.05), but the horses receiving the high hay diet maintained a higher potassium concentration during exercise (P<0.05). Sodium was not affected by diet or exercise (P>0.05). Plasma chloride concentration decreased during exercise (P<0.05). The increased water intake and lower plasma protein concentration associated with the hay diet may be beneficial for horses involved in endurance type exercise.
Performance at high altitude of horses and mules receiving fat supplemented diets
Authors: WICKLER S. J. , PAULEY P. S. , BRAY R. E. , LONDON C. , GABBARD MARIE
Published: June 2010

The purpose of this study was to 1) evaluate and compare the athletic performance of 14 horses and 16 mules, working at high altitude (2700 to 4000 m) in the course of a commercial pack station routine and 2) assess the effect of fat supplementation (10% by weight) on performance. Lactate, haemoglobin, glucose and free fatty acid (FFA) concentrations were measured on Day 1 (prior to supplementation, animals at rest) and then each day thereafter from day 3–7 (i.e. a total of 6 samples for each animal) after an exercise test. Exercise tests ranged in power requirements from 160–730 J/s. Lactate concentrations were increased after the exercise bouts (P=0.029) and were positively correlated (r=0.93) to power. However the value for lactate concentrations indicated that these animals were working well below maximal intensities (mean ± s.e. 1.19 ± 0.1 mmol/l at the most intense work load) and there were no differences between mules and horses. Haemoglobin concentrations were also correlated with power (r=0.79). Glucose and FFA concentrations were increased after exercise. Fat supplemented animals maintained blood glucose concentrations higher than controls and had higher FFA concentrations after the first exercise bout. The only difference between mules and horses was noted after the most intense exercise period: FFA concentrations were higher in mules than horses during exercise.
Effects of weight and riding on workload and locomotion during treadmill exercise
Authors: VAN OLDRUITENBORGH‐OOSTERBAAN MARIANNE M. SLOET , BARNEVELD A. , SCHAMHARDT H. C.
Published: June 2010

To answer the question whether an experienced rider or a dead weight influences a horse's workload and/or its locomotion, 9 well trained Dutch Warmblood horses, fully accustomed to treadmill exercise, underwent a submaximal standardised treadmill exercise test under 3 different conditions: unloaded, mounted by an experienced rider of 90 kg and loaded with 90 kg of lead. Heart rate was monitored continuously and plasma lactate concentrations were determined in venous jugular blood samples immediately before and 2 and 10 min after exercise. Temporal and angular stride variables were measured in fore‐ and hindlimbs at the walk (1.7 m/s), trot (4.0 m/s) and canter (7.0 m/s) with a modified CODA‐3 computerised kinematic analysis system. Peak heart rates during exercise, and recovery heart rates thereafter were significantly lower in the unloaded horses compared to the mounted and lead‐loaded horses. Plasma lactate concentrations immediately and 10 min after exercise were also significantly lower in the unloaded horses than in the mounted and lead‐loaded horses. No differences were found in heart rate and plasma lactate concentration between the mounted and lead‐loaded horses. Relative stance duration increased comparing the unloaded to the mounted and the lead‐loaded horses (P<0.05). Small, but significant, differences were also observed in the fetlock extension and the maximal fetlock range of motion; both increased with loading. In conclusion, an experienced rider and a dead weight influence both workload and locomotion in exercising horses. Minimal differences were found between dead lead weight and a rider.
Indices of exercise capacity in horses presented for poor racing performance
Authors: ROSE R. J. , KING C. M. , EVANS D. L. , TYLER C. M. , HODGSON D. R.
Published: June 2010

We examined 106 Thoroughbred (TB) and 51 Standardbred (SB) racehorses that were presented because of poor performance. All horses were in training and had raced within 2 weeks of presentation. Horses were acclimatised (2–4 runs) and tested on a treadmill set at a 10% slope. The exercise test consisted of 3 min at 4 m/s, 2 min at 6 m/s, then 1 min steps at 8, 10, 11, 12 and 13 m/s or until the horse could not maintain pace with the treadmill. At the end of each speed, arterial blood and expired gas samples were collected and heart rate recorded. Measurements during the test included: arterial blood gas tensions, plasma lactate concentration [LA], V̇O2, V̇CO2, O2 pulse (V̇O2/HR), heart rate, maximum stride length (SLmax), post exercise haematocrit (PCVPE), total red cell volume (CV) and total run time. The TB ran longer than SB (522 vs. 477 s) and had higher values for CV, PCVPE, V̇O2max, V̇O2‐200, maximum O2 pulse, V200, VHRmax, post exercise [LA] ([LAPE]) and SLmax. There were no breed differences for VLA4 and PaO2 at 10 m/s. In the TB, significant correlations (Spearman's rank order) (P<0.01) were found for treadmill run time with: PCVPE, V̇O2max, V̇O2–200, peak O2 pulse, PaO2 at 10 m/s, PaCO2 at 10 m/s, V200, VLA4, [LAPE], VHRmax, maximum blood temperature and SLmax. In the SB significant but lower correlations (P<0.05) were found for treadmill run time with: PCVPE, V̇O2max, V200, VLA4, [LAPE], VHRmax, maximum blood temperature and SLmax. While these results may not be applicable to normal racehorses, the indices which correlated best with treadmill run time were generally those indicating a high capacity for oxygen transport.
Effects of exercise on erythrocytes in normal and splenectomised Thoroughbred horses
Authors: HANZAWA K. , KUBO K. , KAl M. , HIRAGA A. , WATANABE S.
Published: June 2010

Changes in erythrocyte quality during exercise were determined in 3 control (Group C) and 3 splenectomised (Group 5) horses that performed an incremental exercise test on a treadmill until the point of fatigue. Venous blood samples were drawn before the exercise test and immediately after warming‐up and incremental exercise test. Incremental exercise increased erythrocyte count and haemoglobin concentration by 46 and 37% respectively in control horses and by 15 and 17% respectively inGroup Sanimals. Packed cell volume (PCV) increased by 48% in controls but there was no change inGroup Sanimals. Warming‐up decreased mean cell volume (MCV), mean cell Hb (MCH) and mean cell Hb concentration (MCHC) by 9, 19 and 7% in control horses. Incremental exercise restored MCV and MCHC but MCH remained lower than the resting level. InGroup Shorses, warming‐up and incremental exercise decreased MCV by 6 and 9% respectively, did not change MCH, but increased MCHC by 4 and 15% respectively. Incremental exercise increased erythrocyte density (ED) inGroup Cbut not inGroup Shorses. Osmotic fragility of erythrocytes measured as the red cell haemolysis rates in 0.56% NaCl (HL) were significantly higher inGroup Cthan inGroup Shorses regardless of exercise. Warming‐up decreased HL by 7% inGroup Cvs 19% inGroup Shorses, but exercise increased HL by 26% inGroup Cvs 38% inGroup Shorses. These results suggest that: 1) exercise causes shrinking of erythrocytes; 2) erythrocyte indices are dependent on the intensity of the exercise; 3) release of erythrocytes from the spleen is associated with an increase in osmotic fragility; and 4) exercise changes osmotic fragility regardless of the release of erythrocytes from the spleen into circulation.
Acclimation to treadmill exercise
Authors: KING C. M. , EVANS D. L. , ROSE R. J.
Published: June 2010

Acclimation to treadmill exercise and to a respiratory gas collection mask were studied in 3 groups of Thoroughbred or Standardbred horses. Heart rate and plasma lactate concentration were measured at rest and at the completion of each speed increment during a series of acclimating runs at 4, 6 and 8 m/s on a treadmill inclined at a 10% slope. No significant differences were found in the heart rate at 4, 6 or 8 m/s between acclimating runs for any of the groups, except for a reduction between runs 1 and 2 at 4 m/s in a group of 19 racehorses that received 2 acclimating runs (Group 1). Heart rate values at 4 and 6 m/s were significantly higher during the subsequent exercise test in a group of 12 racehorses that received 4 prior acclimating runs (Group 3). Plasma lactate concentration was significantly reduced at 4 and 6 m/s from run 1 to 2 in Group 1 and at all speeds in a group of 6 experimental horses (Group 2) between run 1 and subsequent runs. There was also a significant reduction in plasma lactate concentrations at 6 and 8 m/s between runs 2 and 4 in Group 2 and between runs 3 and 4 at 8 m/s. A temperament scoring system was used to describe the behaviour of the horse on the treadmill. With the exception of 1 horse, the temperament score improved significantly, indicating acclimation to the treadmill after the first acclimating run in Groups 2 and 3. We conclude that acclimation occurred in the majority of horses after 1 or 2 exposures to treadmill exercise and a gas collection mask. However, there was substantial variability between horses and care must be taken when interpreting submaximal heart rate and plasma lactate data. This has important implications for the use of common measurements of exercise capacity such as V200 and VLA4, which rely on values obtained during submaximal exercise.
Modelling impact‐initiated wave transmission through lung parenchyma in relation to the aetiology of exercise‐induced pulmonary haemorrhage
Authors: SCHROTER R. C. , LEEMING A. , DENNY E. , BHARATH A. , MARLIN D. J.
Published: June 2010

Recently we proposed that exercise‐induced pulmonary haemorrhage (EIPH) results from locomotory‐impact‐induced trauma by impact of the scapula on the chest wall during footfall and the consequent transmission of waves through the lung. A computational model has been developed to demonstrate that wave amplification and focusing occur in the dorsocaudal tip of the lung for waves originating on the anterior subscapular surface. The propagation of an acoustic wave was investigated in a simplified 2‐dimensional representation of a vertical anterio‐dorsal section of horse lung. It was demonstrated that a complicated pattern of waves is transmitted from the scapula to the dorsal region. Wave motion was characterised using the instantaneous rate of change of pressure with time (dp/dt) which is associated with lung injury. Due to wave reflection and focusing, dp/dt is transiently very high on the spinal and diaphragmatic lung walls, particularly in the vicinity of the dorsal tip. The model therefore predicts that lung injury may occur in the region in which EIPH is reported to originate.
Is ventilation during maximal exercise limited by dynamic airway closure?
Authors: HOBO S. , HIRAGA A. , BIRKS E. K. , TAKAHASHI T. , HADA T. , JONES J. H.
Published: June 2010

A study was undertaken to And if the reason why horses hypoventilate when running is that they experience expiratory flow limitation due to dynamic airway closure. To test this hypothesis, we measured peak expiratory flows on a Thoroughbred galloping on a treadmill and hypoventilating and compared those flows with the peak dynamically‐limited flow that the same horse could achieve during a forced expiratory flow‐volume manoeuvre. At the approximate lung volumes at which the horse was ventilating while running, it did not appear to be mechanically limited and appeared to have reserve capacity available potentially to increase its expiratory flow.
Pathophysiology of dorsal displacement of the soft palate in horses
Authors: HOLCOMBE SUSAN J. , DERKSEN F. J. , STICK J. A. , ROBINSON N. E.
Published: June 2010

Dorsal displacement of the soft palate (DDSP) is an intermittent obstructive upper airway condition that occurs in athletic horses during high‐intensity exercise. The pathogenesis of this condition is unknown, but may involve epiglottic hypoplasia, malformation, or neuromuscular dysfunction. In this paper, we report on investigations into the pathophysiology of DDSP. In 3 separate experiments, Standardbred horses were exercised on a high‐speed treadmill at speeds corresponding to 50, 75 and 100% of maximum heart rate. The upper airway was evaluated by videoendoscopy and measurement of tracheal pressures.

Inexperiment 1, we examined the effect of bilateral hypoglossal and glossopharyngeal nerve block on epiglottic function in exercising horses. This nerve block caused epiglottic retroversion and inspiratory upper airway obstruction. However, DDSP did not occur. Inexperiment 2, we evaluated the hypothesis thattensor veli palatinimuscle dysfunction is involved in the pathogenesis of DDSP. Bilateraltensor veli palatinimuscle tenectomy did not cause DDSP, but caused instability of the rostral half of the soft palate and a modest inspiratory upper airway obstruction. Inexperiment 3, we hypothesised thatpalatinusand palatopharyngeal dysfunction causes DDSP. The pharyngeal branch of the vagus nerve was blocked bilaterally in the guttural pouch. This block caused DDSP in all horses within 2–15 min after nerve block. Furthermore, DDSP created an expiratory nasopharyngeal obstruction. Because the pharyngeal branch of the vagus nerve is in close proximity to the retropharyngeal lymph node chain, we suggest that retropharyngeal lymphadenopathy may cause neural dysfunction and thereby be involved in the pathogenesis of clinical DDSP.
Differences in the ventilatory responses of horses and ponies to exercise of varying intensities
Authors: KATZ LISA M. , BAYLY W. M. , HINES MELISSA T. , SIDES R. H.
Published: June 2010

Horses exercising at ˜90% V̇o2maxdevelop arterial hypoxaemia with concurrent hypercapnoea, whereas ponies exercising at comparative levels become hypocapnoeic and maintain arterial oxygen tensions close to resting values. We sought to investigate the possibility that these differences relate to the ventilatory responses of these animals to exercise. Six Thoroughbred horses weighing mean ± s.e. 501 ± 27 kg and 5 ponies weighing mean ± s.e. 164 ± 18 kg exercised for 2 min on a 10% slope at speeds calculated to require 60% V̇o2maxand for at least 1 min at speeds calculated to require 115% V̇o2max. Oxygen consumption (V̇o2), arterial oxygen (Pao2) and carbon dioxide (Paco2) tensions, acid‐base balance, tidal volume (VT), minute ventilation (V̇E), peak inspiratory (V̇Imax) and expiratory (V̇Emax) flow, and maximal changes in transpulmonary pressures (ΔPtpmax) were measured immediately before exercise and in the last 15 s of exercise at each intensity. The results confirmed that, unlike horses, ponies do not become hypoxaemic or hypercapnoeic during exercise. Despite having a higher ΔPtpmax, higher V̇Imaxand V̇Emaxand V̇E/kg0.75at the same relative intensities, horses were less capable of mounting an appropriate ventilatory response to exercise. This was reflected by lower mass specific and metabolic weight‐based ventilations at similar absolute workloads, and their higher Paco2and arterial [HCO3−]> and lower ventilatory equivalent for oxygen (V̇E/V̇o2). This suggests that horses become hypoxaemic and hypercapnoeic at work loads ˜90% V̇o2maxbecause their metabolic demand surpasses the capacity of their ventilatory system to meet this demand. Because ponies are less capable athletes, they can match their ventilatory response to their metabolic requirements.
Cardiorespiratory measurements and indices of oxidative stress in exercising COPD horses
Authors: ART TATIANA , KIRSCHVINK NATHALIE , SMITH NICOLA , VOTION DOMINQUE , LEKEUX P.
Published: June 2010

The effect of a COPD crisis on arterial blood gases, heart rate, lactate and indices of oxidative stress were investigated before, during and 1 h after a ‘run up to fatigue’ in 6 COPD horses. They were investigated twice, randomly: once in acute crisis (C) and once in clinical remission (R). Arterial and mixed venous blood samples were collected and analysed for partial pressures in O2 and CO2. The mixed venous blood was also analysed for plasma lactate (LA) and packed cell volume (PCV), as well as for indices of oxidative stress, i.e. reduced glutathione, glutathione disulphide, glutathione redox ratio (GRR) and lipid hydroperoxides (LPH). The exercise test was an effort of increasing intensity on a treadmill at 0% slope, which was stopped when the horses showed signs of exhaustion. Their performance was evaluated by the number of steps and the running time in the last step. Heart rate was monitored continuously during the test Blood sampling was performed before, just after and 1 h after the end of the test.

The COPD crisis significantly reduced the time to fatigue. However, despite the fact that the exercise intensity and length were lower, peak HR and peak LA were similar in C and R, while arterial hypoxaemia and hypercapnia, and PCV were significantly higher in C, indicating a higher physiological stress in this condition. By contrast, the oxidative stress seemed to be higher in R than in C as suggested by the fact that, 1 h after exercise, GRR and LPH were significantly increased with regards to their pre‐exercise values in R and not in C. The fact that exercise did not induce an oxidative stress in C could be partly related to (1) the lower exercise intensity reached by the horses, and (2) to the more severe hypoxaemia experienced in this condition.

In conclusion, COPD horses in acute crisis show a significant decrease in performance. The reasons for this exercise intolerance remain unclear, but do not appear to be related to any increase of the oxidative stress in C.
Changes in left ventricular dynamics during graded exercise
Authors: HIRAGA A. , HOBO S. , BIRKS E. K. , TAKAHASHI T. , HADA T. , SMITH B. L. , CARR E. A. , PASCOE J. R. , JONES J. H.
Published: June 2010

Three mature Thoroughbred horses were prepared surgically with ultrasonic sonomicrometer crystals affixed to their ventricular pericardia. Signals from crystals recorded dimensions of axes across the left ventricle. Cubic algorithms were fitted to dimensional data to generate volume estimates that matched stroke volumes simultaneously measured using the Fick principle. As horses stood at rest or exercised at various intensities (approx 7, 12, 24, 47 and 100% maximal rate of O2consumption [V̇o2max]), left ventricular dimensions were recorded and 20 consecutive diastolic and systolic volumes calculated. Although Fick estimates detected no difference in stroke volume at different exercise intensities, sonomicrometer measurements of stroke volume were significantly lower at rest and higher at V̇o2max. These differences mirrored changes in end‐diastolic volume, although end‐systolic volume did not change. At all exercise intensities, stroke volume was most variable and end‐diastolic volume the least. The pattern conforms to the Frank‐Starling mechanism, and indicates that at high exercise intensities ventricular myocytes generate high pressures with higher myocardial wall stress due to the increased size of the chamber.
Cardiac output measurements using sonomicrometer crystals on the left ventricle at rest and exercise
Authors: PASCOE J. R. , HIRAGA A. , HOBO S. , BIRKS E. K. , YARBROUGH T. B. , TAKAHASHI T. , HADA T. , AIDA H. , STEFFEY E. P. , JONES J. H.
Published: June 2010

Eight horses were fitted surgically with 8 ultrasonic sonomicrometer crystals each attached to their left ventricular pericardia and a left atrial catheter. Three horses returned to treadmill performance with a maximum rate of oxygen consumption similar to their presurgical values. These horses were evaluated to determine how well sonomicrometer estimates of cardiac output agreed with those obtained by a steady‐state method, the Fick principle. Variance between the 2 was similar to the coefficient of variation (approximately 12.5%) of the Fick estimates. We conclude that left ventricular sonomicrometer measurements in horses appear to give a reasonable estimate of ventricular dimensions and can, therefore, be used potentially to evaluate such variables as diastolic flow.
Oral nitroglycerin paste did not lower pulmonary capillary pressure during treadmill exercise
Authors: HACKETT R. P. , DUCHARME N. G. , GLEED R. D. , ERB H. N. , MITCHELL L. M. , SODERHOLM L. V.
Published: June 2010

We hypothesised that 22.5 mg of oral nitroglycerin would cause pulmonary vasodilation and therefore decrease pulmonary capillary pressure in horses during strenuous exercise. Six horses were assigned to exercise twice, once with no medication (control) and once with nitroglycerin (22.5 mg orally) in random order. Horses were exercised for 3 min each at 75, 90 and 100% of maximal heart rate (HRmax) with a 2 min period of walking between each period of exertion. Pulmonary artery and oesophageal pressures were recorded continuously. Subsequent analysis was carried out on the pulmonary arterial pressure signal with the oesophageal pressure subtracted, hence pulmonary vascular pressures reported in this paper approximate transmural pressures. Pulmonary arterial pressure, pulmonary arterial wedge pressure, pulmonary capillary pressure, heart rate and arterial blood gas tensions were determined for each level of exercise. Pulmonary arterial wedge and pulmonary capillary pressures were determined from the pulmonary artery waveform after dynamic occlusion of a branch of the pulmonary artery. The resulting decay in pulmonary artery pressure was submitted to an exponential curve fitting and the amplitude at the moment of occlusion on this curve was recorded as pulmonary capillary pressure. The effects of nitroglycerin on the various parameters were evaluated using a 3‐way ANOVA blocked on horse treatment, and exercise intensity, followed by Tukey's multiple comparison procedure. Resting pulmonary artery pressure decreased from mean ± s.e. 34.0 ± 5.5 mmHg to 24.0 ± 3.9 mmHg 5 min after administration of nitroglycerin (P<.05) but there were no significant effects on pulmonary capillary or wedge pressures. Nitroglycerin at this dose resulted in no significant differences in pulmonary artery, pulmonary capillary, and pulmonary wedge pressure, heart rate, arterial oxygen tension or arterial carbon dioxide tension at 75, 90 and 100% of HRmax. This dose of nitroglycerin does not appear significantly to protect the pulmonary vascular bed from exercise‐induced hypertension. These data do not support the use of this dose of oral nitroglycerin in the prevention of EIPH.
Influence of frusemide on dynamic cardiac variables during exercise
Authors: LANGSETMO INGRID , WEIGLE G. E. , ERICKSON H. H. , FEDDE M. R.
Published: June 2010

Exercising horses have extremely high right and left atrial pressures. Limitation in ventricular function (i.e. relaxation) may play a role in these high pressures. We studied relaxation characteristics of the right ventricular myocardium and the impact of frusemide (2.0 mg/kg bwt i.v.) on these characteristics in horses exercising at 8, 10, 12 and 14 m/s. Exercise tests were performed 4 h after administration of frusemide. Right ventricular (RV) pressure was analysed using Fast Fourier Transform techniques to remove non cardiac components of the pressure signal. Mean right atrial (RA) pressure increased with exercise and was significantly attenuated at all speeds by frusemide. RV maximum and minimum rates of pressure change with respect to time (RV+dP/dtmax, RV‐dP/dtmax) increased with exercise and RV relaxation time constant (RVτ) and time of RV relaxation from 65–20% of the difference between maximum and minimum ventricular pressure (Δ65–20) decreased with exercise. Frusemide produced no significant differences in +dP/dtmax, ‐dP/dtmax, RVτor Δ65–20 except at 12 m/s where RVτwas longer after frusemide (23.4 ms for frusemide vs. 19.7 ms for control). Significant reductions in stroke volume were seen at 8, 10 and 14 m/s after frusemide. These results suggest that the reduction of atrial pressure by frusemide is not due to changes in ventricular relaxation rate.
Effects of pre‐exercise frusemide administration and post exercise anaesthesia on cardiopulmonary and acid‐base parameters and blood and plasma volumes in horses exercised supramaximally to fatigue
Authors: KEEGAN R. D. , GREENE S. A. , BROWN J. A. , WEIL A. B. , BAYLY W. M.
Published: June 2010

Six horses were randomly assigned to receive either frusemide (F) (0.5 mg/kg i.v.) or an equivalent volume of saline (S) i.V., 4 h prior to treadmill exercise. Horses were instrumented to enable measurement of heart rate (HR), systolic (SAP), mean (MAP), and diastolic (DAP) carotid arterial pressures, pulmonary artery pressure (PAP), central venous pressure (CVP), pulmonary arterial temperature (TEMP), blood gases, and cardiac output (CO). Plasma (PV) and blood volumes (BV) were measured using 2 injections of Evan's Blue dye. Baseline parameters were recorded while the horse stood quietly. Horses were then administered F or S. Four hours later, they were warmed up for 3 min at 4 m/s and then exercised to the point of fatigue at 115% V̇o2max. Horses were anaesthetised immediately following exercise by administration of detomidine (0.04 mg/kg bwt i.v.) followed 5 min later by tiletamine‐zolazepam (1.25 mg/kg bwt i.v.). After transporting the horse to a recovery stall, anaesthesia was maintained with isoflurane in 100% O2. Data were analysed using a 2‐way ANOVA with repeated measures withpost hocdifferences identified using the Student‐Newman‐Keul's procedure. Exercise was associated with increases in HR, SAP, MAP, DAP, PAP, CVP, TEMP, PCV, and BV, and decreases in PV, pH, arterial bicarbonate and base excess. Anaesthesia was associated with marked hypercapnia, a decrease in HR following detomidine administration, and persistent pulmonary hypertension despite carotid arterial pressure which returned to baseline. No effects attributable to F were identified at any time during the study.
Influence of training on autonomic nervous function in horses: evaluation by power spectral analysis of heart rate variability
Authors: KUWAHARA M. , HIRAGA A. , KAI M. , TSUBONE H. , SUGANO S.
Published: June 2010

We studied the influence of training on autonomic nervous function in the horse. For this purpose, Holter electrocardiogram (ECG) was recorded before and after training from 24 Thoroughbred horses (2‐year‐olds) and autonomic nervous function was evaluated by the power spectral analysis of heart rate (HR) variability. We obtained HR, low‐frequency (LF) power, high‐frequency (HF) power, and LF/HF ratio from recording. We set LF at 0.01–0.07 Hz and HF at 0.07–0.6 Hz. The HF power is thought to reflect primarily parasympathetic nervous function. Both the sympathetic and parasympathetic nervous systems have been shown to contribute to the LF power. The LF/HF ratio is considered as an index of the cardiac sympathovagal balance. Second degree atrioventricular blocks were found in the ECG of 3 and 5 horses before and after the training period, respectively. Ventricular premature depolarisations were detected in a horse after the training period. Heart rate decreased at night The lowest HR values had a tendency to appear in the early morning. Both the LF and HF power tended to be higher at night However, the LF/HF ratio was almost the same throughout the day. The HR was significantly decreased by training. Although the LF power and LF/HF ratio were significantly increased, the HF power was not changed by training. These results suggest that parasympathetic nervous activity may be fully activated even before training in this species.
The effect of supramaximal exercise on equine platelet function
Authors: KINGSTON JANENE K. , SAMPSON SARAH N. , BEARD LAURIE A. , MEYERS K. M. , SELLON DEBRA C. , BAYLY W. M.
Published: June 2010

When blood is collected into sodium citrate in the proportion of 9 parts blood:1 part sodium citrate, the concentration of plasma sodium citrate in the sample will depend on the packed cell volume (PCV) of the blood sample. This difference in plasma sodium citrate concentration secondary to alterations in PCV significantly affects human platelet aggregation responses. Since horses attain a high PCV in response to high‐intensity exercise we investigated the effect of differences in sample plasma sodium citrate concentration on equine platelet aggregability. In addition, low molecular weight heparin (LMWH) was evaluated as an alternative anticoagulant for assessment of platelet aggregability during strenuous exercise in horses. Blood samples were collected pre‐exercise and at fatigue after supramaximal treadmill exercise into either 3.8% sodium citrate (9 parts blood:1 part sodium citrate) or 20 u LMWH/ ml of blood. Platelet aggregation responses to 1.25 μmol/l adenosine diphosphate (ADP) were measured via optical aggregometry. For samples collected into sodium citrate, aggregability was significantly less than pre‐exercise values in samples collected at fatigue and in pre‐exercise samples in which sodium citrate concentrations were adjusted to equal those in fatigue samples. However, samples collected into LMWH showed significantly increased platelet aggregability in samples collected at fatigue when compared to pre‐exercise samples. In conclusion, higher plasma sodium citrate concentration had a marked inhibitory effect on equine platelet aggregation responses. Low molecular weight heparin was a good alternative anticoagulant for assessment of equine platelet function and results indicate that equine platelet aggregability was enhanced in response to supramaximal exercise.
Plasma atrial natriuretic peptide during and after repeated exercise under heat exposure
Authors: KOKKONENt U.‐M. , HYYPPä S. , PÖSÖ A. REETA
Published: June 2010

Plasma atrial natriuretic peptide (ANP) responses were studied in horses during and after a competition exercise test (CET) designed to simulate the endurance test of a 3‐day event and including testPhases A‐D.CET was repeated 5 times at 2 week intervals at mean temperature +28°C and relative humidity (RH) 58%. Heart rate (HR) was monitored during CET. After CET, the horses were rehydrated with isotonic glucose‐electrolyte solution or water. ANP, NH2‐terminal pro‐atrial natriuretic peptide (NT‐ANP), aldosterone, arginine vasoapressin (AVP) and plasma proteins (PP) were measured during CET and recovery. ANP rose with intensity and duration of exercise from 8 pmol/l to 15 pmol/l at a gallop (Phase B), remained elevated atPhases C‐X, and peaked (23 pmol/l) at a canter (Phase D). Thereafter, ANP decreased to the pre‐exercise level within 2.5 h irrespective of rehydration. Repeated exercise bouts failed to affect plasma ANP, although other adaptive changes occurred. No diurnal variation in plasma ANP appeared. In NT‐ANP, the most marked elevation occurred duringPhases C‐D.In contrast to ANP, the decrease was minor for 1 h after the canter. ANP did not correlate with AVP or HR. In conclusion, exerciseper seaffected equine plasma ANP but the possible effect of thermal stress could not be demonstrated. The differences between ANP and NT‐ANP responses indicate differences in their release or elimination and suggest that the cardiac prohormone cleavage may occur intracellularly or simultaneously with secretion, not in circulation.
Relationship between V̇O2max, heart score and echocardiographic measurements obtained at rest and immediately following maximal exercise in Thoroughbred horses
Authors: SAMPSON SARAH N. , TUCKER R. L. , BAYLY W. M.
Published: June 2010

We evaluated the relationships of heart score (HS) and echocardiographic measures to maximal oxygen consumption (V̇o2max), maximal cardiac output (Q̇max), and maximal stroke volume (SVmax). Six fit, mature Thoroughbred horses weighing (mean ± s.e.) 487 ± 11 kg were run 4 times on an inclined (10%) treadmill. Each run consisted of a 3 min warm‐up at 4 m/s followed by completion of an incremental exercise test in which each horse ran until V̇os2max was reached. Arterial and mixed venous blood was collected to determine arteriovenous oxygen content difference [C(a‐v)o2] in the last 15 s of exercise. An ATL HDI 3000 ultrasound system and a 3.5 MHz phased array transducer were used to make echocardiographic measurements before and within 2 min of run completion. Guided M‐mode echocardiographic measurements of left ventricular diameter (LVD), interventricular septal thickness (IVS) and left ventricular free wall thickness (LVFW) during diastole (D) and systole (S) were made from the right parasternal short axis view at the level of the chordae, and V̇o2 and C(a‐v)o2 were measured as the appropriate M‐mode view was recorded. Maximum heart rate (HRmax) was determined using a cardiotachometer, and HS was calculated on nonexercise days using the established technique. Maximum cardiac output and SVmax were calculated from the Fick equation and HRmax. Backward stepwise regression analysis was used to relate pre‐ and post exercise echocardiographic measurements and HS to V̇o2, Q̇, and SV at the time of measurement, and to V̇o2max, Q̇max, and SVmax. Pre‐ and post exercise LVDD appeared to be the most important variable in these equations. Mean pre‐exercise HR at the time of measurement was 54.7 ± 1.9 beats/min, while the mean post exercise rate was 111.7 ± 2.6 beats/min. The mean ± s.e. V̇o2max was 150.4 ± 13.2 ml/(kg.min). Heart score was not correlated with V̇o2max, Q̇max, or SVmax. There was no significant difference between pre‐ and post exercise measurements of LVD, IVSS, and LVFWS.
Should equine athletes commence training during skeletal development?: changes in tendon matrix associated with development, ageing, function and exercise
Authors: SMITH R. K. , BIRCH HELEN , PATTERSON‐KANE J. , FIRTH E. C. , WILLIAMS L. , CHERDCHUTHAM W. , WEEREN W. R. van , GOODSHIP A. E.
Published: June 2010

In human athletes, conditioning, training and competition are commenced before skeletal maturity. Yet in equine athletics, racing of young (age 2 years) horses remains contentious. Tendon injury persists as major causes of wastage in equine athletes. Minimising injury and associated welfare issues could involve a radical approach to the timing and implementation of conditioning and training. Tendons were examined from Thoroughbreds, Dutch Warmblood foals, working horses and also a group of wild horses to evaluate effects of age, function and exercise. Gross mechanical properties did not differ significantly with age or exercise, but showed a high variance within each group. Mechanical properties of tendon tissue showed significant differences as a function of age and location. The collagen fibril crimp angle and length showed a regional reduction in the central core with exercise and age, with a synergistic effect. Regional differences in collagen fibril diameter were seen in long‐term exercised older horses, but not in short‐term exercised, or younger, horses. The higher proportion of small fibrils in the central region of the long‐term exercised horses did not correlate with new collagen formation and therefore appear to result from disassembly of the larger diameter fibrils. Fibril diameter distributions were influenced by exercise regimens in the growing foal. Changes in molecular composition occurred in longer‐term exercise and older horses, in the centre of the tendon, with higher levels oftype IIIcollagen and changes in glycosaminoglycan (GAG) content. Cartilage Oligomeric Matrix Protein (COMP) levels also appear to be modulated by age, function and superimposition of exercise. These changes were all exacerbated with age and exercise, suggesting appropriate exercise in young horses may lead to a lower incidence of injury than in older horses. An hypothesis is advanced that immature tendon can respond to exercise while mature tendon has limited, if any, ability to do so. These findings support potentially controversial earlier conditioning and racing of younger, rather than older, equine athletes.
Kinematics of the equine back: flexion‐extension movements in sound trotting horses
Authors: AUDIGIÉ F. , POURCELOT P. , DEGUEURCE C. , DENOIX J. M. , GEIGER D.
Published: June 2010

This study was undertaken to evaluate the flexion‐extension movements of the back in a group of sound trotting horses. Using a 3‐D kinematic analysis system, 13 clinically sound horses fitted with 5 skin markers placed on the dorsal midline of their trunk were recorded while trotting on a track in the conditions of the routine lameness examination. These markers were used to calculate 3 back angles (thoracic, thoracolumbar and lumbosacral angle). These back angles were then filtered using Fourier series. To evaluate the repeatability of flexion‐extension movements, the intra‐ and inter‐individual variabilities were studied. The angle‐time diagrams showed that the equine back extended during the first part of each diagonal stance phase and flexed during the second part of each diagonal stance phase. The ranges of motion were less than 4° for the 3 back angles. The intra‐ and inter‐individual variability values of maximal extension and maximal flexion time points were similar and extremely low. This demonstrates the high repeatability of the temporal pattern of flexion‐extension movements of the back. Intra‐and inter‐individual variabilities of the range of motion showed that the back mobility varies more in‐between horses than between trials of the same horse. Compared with electromyographic activities of back muscles reported in the literature, flexion‐extension movements described in this study tend to show that, at a slow trot, trunk muscles act mainly to limit flexion‐extension movements of the back rather than to induce movements.
Influence of rough track surfaces on components of vertical forces in cantering Thoroughbred horses
Authors: KAI M. , TAKAHASHI T. , AOKI O. , OKI H.
Published: June 2010

No kinetic data are available to indicate the influence of a rough track surface and the resultant loss of footing on the components of hoof vertical forces. The aim of the present study was to evaluate the influence of rough track surfaces on the components of hoof vertical forces. Seven clinically sound 2‐year‐old Thoroughbred horses had instrumented shoes attached to both of the fore hooves to obtain the magnitudes of consecutive forces exerted in the hoof. All horses were cantered at approximately 10 m/s on straight tracks of smooth and rough surfaces of woodchip and dirt. The instrumented shoe indicated in real time 4 component forces acting on the hoof via 4 transducers positioned on the lateral and medial sides of the toe (LT, MT) and the heel (LH, MH). The peak vertical component forces of the heel were about twice that of the toe. The variances of the 4 components of peak vertical forces significantly increased on the rough track surface of both the woodchip (Leading: LH, MH and MT; Trailing: MH and LT) and dirt (Leading: LH and LT; Trailing: MH and MT) tracks. The trajectories of the position of the resultant force acting on the hoof also tended to increase the variance on rough track surfaces. Therefore, running on a rough track changes the vertical hoof forces and the balance of the resultant hoof forces. These results suggest a mechanism by which the rough track surfaces may influence the soundness of the horse.
Treadmill exercise‐induced tendon hypertrophy: assessment of tendons with different mechanical functions
Authors: BIRCH HELEN L. , McLAUGHLIN LUCY , SMITH R. K. W. , GOODSHIP A. E.
Published: June 2010

The equine superficial digital flexor tendon (SDFT) functions as an energy store during high‐speed gaits reducing the energetic cost of locomotion. To enable the SDFT to function effectively, the appropriate mechanical properties are essential. We tested the hypothesis that the SDFT does not undergo gross hypertrophy in response to high‐intensity exercise whereas tendons not involved in energy storage undergo adaptive hypertrophy. Two groups (n=6) of Thoroughbred fillies were trained at high‐intensity on a highspeed equine treadmill for 5 months (short‐term study) or 18 months (long‐term study). Age‐matched groups (n=6) of horses undertook low‐intensity exercise only for the same time period. Throughout the short‐term study the SDFT and deep digital flexor tendon (DDFT) were ultrasonograpically scanned at mid‐metacarpal level and cross‐sectional area (CSA) calculated. At the end of the short‐term study (horse age=2 years) and long‐term study (horse age = 3 years) the left SDFT, DDFT, suspensory ligament (SL) and common digital extensor tendon (CDET) were harvested and CSA calculated. Comparison of the DDFT from 2‐ and 3‐year‐old horses revealed an age‐related increase in CSA which was confirmed by ultrasonographs.Post mortemanalysis showed a significant hypertrophy of the CDET with high‐intensity training in the short‐term study (younger horses). CSA did not differ significantly between training groups for any of the structures following long‐term training. These results suggest a structure specific hypertrophic response to the imposed training regime.