Influence of cyclooxygenase inhibitors on furosemide-induced hemodynamic effects during exercise in horses.

Furosemide, which commonly is used as a prophylactic treatment for exercise-induced pulmonary hemorrhage in horses, may mediate hemodynamic changes during exercise by altering prostaglandin metabolism. To determine if furosemide's hemodynamic effects during exercise in horses could be reversed, cyclooxygenase inhibitors were administered with furosemide. Four treatments were administered 4 hours prior to treadmill exercise at 9 and 13 m/s. They included a control treatment (10 ml of 0.9% NaCl solution, IV), furosemide (1 mg/kg of body weight, IV) administered alone, and furosemide in combination with phenylbutazone (4 mg/kg, IV, q 12 h for 2 days) or with flunixin meglumine (1.1 mg/kg, IV, on the day of experiment). Five horses were randomly assigned to complete all treatments. Physiologic variables at rest prior to exercise were not influenced by treatments. Furosemide, administered alone, reduced mean right atrial pressure and mean pulmonary artery pressure during exercise. The combinations of furosemide and flunixin meglumine or furosemide and phenylbutazone, at both levels of exercise intensity, returned mean right atrial pressure and mean pulmonary artery pressure to the value of the control treatment. During rest and exercise, plasma lactate concentration, PCV, heart rate, mean carotid artery pressure, oxygen consumption, carbon dioxide elimination, and cardiac output were not altered by any of the treatments. At 5 minutes after exercise, the administration of furosemide, alone or with phenylbutazone, reduced mean right atrial pressure. Other measured variables were not significantly influenced by treatments during recovery from exercise. These results suggested that cyclooxygenase inhibition partially reverses the decrease in mean right atrial pressure or pulmonary artery pressure induced by furosemide during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of furosemide treatment on fluid and electrolyte balance in horses

Alterations in electrolyte and acid-base balance were studied in 6 horses for 8 hours after furosemide administration (1 mg/kg of body weight, IM), and the results were compared with those for 5 healthy untreated horses (controls) kept under identical environmental conditions. In the treated group, decreases in plasma potassium, chloride, and calcium concentrations and increases in total plasma protein content persisted for the 8-hour observation period, whereas there was no change in plasma sodium concentration, osmolality, or packed cell volume. Plasma bicarbonate concentration and PCO2 remained high throughout the study, during which time venous blood pH was modestly increased only at the 6-hour sampling time. Furosemide treatment resulted in decreases in urine pH, specific gravity, osmolality, and potassium and calcium concentrations and increases in urine volume and total urine sodium, chloride, and calcium excretion. Body weight decreased 19.2 +/- 5.2 kg (mean +/- SD) in treated horses (4 +/- 1% of body weight), compared with a weight loss of 8 +/- 2.1 kg in untreated horses (1.5 +/- 0.4% of body weight) during the 8-hour experimental period. The increased fluid losses induced by the diuretic did not cause any obvious clinical signs in the horses. Pulse pressure, skin turgor, capillary refill time, and jugular distensibility remained unchanged throughout the experimental period.     

Equine energetics. II. Energy expenditure in horses during submaximal exercise

Energy expenditure was measured in four geldings (433 to 520 kg) during submaximal exercise on a racetrack using a mobile open-circuit indirect respiration calorimeter. A total of 304 5-min measurements of O2 consumed and CO2 produced were taken. Measurements were made with and without riders. The amount of energy expended by the horses was exponentially related to speed and was proportional to the body weight of the riderless horse or the combined weight of the horse plus rider and tack. Total energy expended by the four horses walking, trotting, cantering was best described by the equation: Y = e3.02 + .0065X where Y = energy expended (cal X kg-1 X min-1) and X = speed (m/min). Digestible energy (DE) required above maintenance was calculated as (Formula: see text).     

Metabolic responses to oral tryptophan supplementation before exercise in horses

This study was conducted to evaluate the effects of oral tryptophan (Trp) supplementation on exercise capacity and metabolic responses in horses. Three horses had to perform an exercise test: a 15-min warm-up followed by a 60-min walk (1.7 m/s, W1), a 10-min trot (3.1 m/s, T1), a second 60-min walk (1.7 m/s, W2), a second 10-min trot (3.1 m/s, T2) and a final 30-min walk (1.7 m/s, W3) until the horses were unwilling to continue. The horses exercised on a treadmill at a 6% incline and with a constant draught load of 40 kg (0.44 kN). Two hours before exercise horses were given 50 g Trp (9.8-10.7 g Trp/100 kg BW) by nasogastric tube. A control exercise test was conducted without Trp. During the control test, one horse was able to finish the final 30-min walk (W3), whereas two horses finished W3 after Trp administration. Higher plasma Trp levels after Trp administration did not change significantly during exercise (Trp: start exercise, 524 +/- 41 micromol/l; end exercise 547 +/- 20 micromol/l; control: start exercise, 70 +/- 10 micromol/l; end exercise, 58 +/- 21 micromol/l). After Trp supplementation, blood lactate concentrations were significantly lower after the first and second trotting periods. Free fatty acids in plasma increased during exercise without any treatment-related differences. Although experimental plasma Trp levels were seven times higher than the control levels, Trp supplementation had no effect on exercise performance and metabolic responses to draught load exercise.     

Endothelin response during and after exercise in horses

The objective of the present study was to measure plasma endothelin-1 (ET-1) at rest and during exercise in the horse. Six healthy, Standardbred and Thoroughbred mares (5.3+/-0.8 years; 445.2+/-13.1 kg) which were unfit, but otherwise accustomed to running on the treadmill, were used in the study. Plasma ET-1 concentrations were measured using a commercially available radioimmunoassay kit. Horses performed three trials: a standing control (CON) trial where blood was collected from the jugular vein every minute for 5 min; a graded exercise test (GXT) where blood samples were collected at the end of each 1 min step of an incremental exercise test; and a 15 min submaximal (60% VO(2max)) steady-state exercise test (SST) where blood samples were collected 1 min before, immediately after, and at 2 min, 10 min and 20 min post-exercise. Plasma ET-1 concentration did not change (P>0.05) during the CON trial where it averaged 0.18+/- 0.03 pg/mL (mean+/-SE). Surprisingly, plasma ET-1 concentration did not change during the GXT trial where it averaged 0.20+/-0.03 pg/mL. There were no differences between the mean concentrations obtained in either trial (P>0.05). Plasma ET-1 concentrations were, however, significantly elevated (P<0.05) immediately following exercise and at 2 min post-exercise in the SST. Post-exercise plasma ET-1 concentrations returned to baseline (P>0.05) by 10 min of recovery. Together, these data may suggest that ET-1 concentrations are altered in response to an exercise challenge.     

Arterial-venous difference in atrial natriuretic peptide concentration during exercise in horses.

Six nontrained mares were subjected to steady-state, submaximal treadmill exercise to examine the effect of exercise on the plasma concentration of atrial natriuretic peptide (ANP) in arterial, compared with mixed venous, blood. Horses ran on a treadmill up a 6 degree grade for 20 minutes at a speed calculated to require a power equivalent to 80% of maximal oxygen uptake (VO2MAX). Arterial and mixed venous blood samples were collected simultaneously from the carotid and pulmonary arteries of horses at rest and at 10 and 20 minutes of exercise. Plasma was stored at -80 C and was later thawed; ANP was extracted, and its concentration was determined by radioimmunoassay. Exercise caused significant (P < 0.05) increases in arterial and venous plasma ANP concentrations. Mean +/- SEM arterial ANP concentration increased from 25.2 +/- 4.4 pg/ml at rest to 52.7 +/- 5.2 pg/ml at 10 minutes of exercise and 62.5 +/- 5.2 pg/ml at 20 minutes of exercise. Mean venous ANP concentration increased from 24.8 +/- 4.3 pg/ml at rest to 67.2 +/- 14.5 pg/ml at 10 minutes of exercise and 65.3 +/- 13.5 pg/ml at 20 minutes of exercise. Significant differences were not evident between arterial or mixed venous ANP concentration at rest or during exercise, indicating that ANP either is not metabolized in the lungs or is released from the left atrium at a rate matching that of pulmonary metabolism.     

Blood lactate responses to submaximal field exercise tests in thoroughbred horses

The associations between velocity during a standardized, submaximal 800-m exercise test and blood lactate concentration after exercise were investigated in Thoroughbred racehorses on sand and grass racetracks. Predicted lactate concentrations for each horse's exercise test velocity were calculated from the line of best fit derived from results at each racetrack. The repeatability of the differences between the measured and predicted blood lactate response to exercise was also investigated. Exercise tests were conducted at speeds ranging from 12.8 to 16.6 m/s. The variability of velocity within the exercise test was expressed as the coefficient of variation (CV) of the times for the four 200-m sections.On the sand track, the coefficient of determination for the lactate-speed relationship was highest for an exponential regression equation [lactate (mmol/L) = 0.08e(0.33x)(m/s);r(2)= 0.58, P< 0.05;n = 21]. Similar coefficients of determination were calculated for linear (r(2)= 0.56) and second order polynomial equations (r(2)= 0. 57). On the grass racetrack, the relationship was best described by a second order polynomial equation [lactate (mmol/L) = -0.87x(2)+ 28. 17x - 211.41;r(2)= 0.57, P< 0.05;n = 25]. The mean differences between the measured and predicted blood lactate concentrations in repeated tests were 1.9 +/- 1.8 (SD) and 1.8 +/- 1.7 ( SD) on the sand and grass racetracks. There were no significant associations between the velocity of the exercise and the CV on either racetrack. Differences between measured and predicted blood lactate concentrations, based on track-specific lines of best fit, have potential application in field studies of fitness in Thoroughbred horses.     

Effect of a tongue-tie on upper airway mechanics in horses during exercise

OBJECTIVE: To determine the effect of a tongue-tie on upper airway mechanics in exercising horses. ANIMALS: 5 Standardbreds. PROCEDURE: Peak inspiratory and expiratory tracheal and pharyngeal pressures and airflow were measured while horses exercised on a treadmill with and without a tongue-tie. Respiratory rate was also measured. Horses ran at speeds that corresponded to 50 (HR50), 75, 90 (HR90), and 100% of maximal heart rate. The tongue-tie was applied by pulling the tongue forward out of the mouth as far as possible and tying it at the level of the base of the frenulum to the mandible with an elastic gauze bandage. Peak inspiratory and expiratory tracheal, pharyngeal, and translaryngeal resistance, minute ventilation, and tidal volume were calculated. Data were analyzed by use of 2-way repeated-measures ANOVA. For post hoc comparison of significant data, the Student-Newman-Keuls test was used. RESULTS: We were unable to detect significant differences between groups for peak inspiratory or expiratory tracheal or pharyngeal resistance, peak pressure, peak expiratory flow, tidal volume, respiratory rate, or minute ventilation. Horses that ran with a tongue-tie had significantly higher peak inspiratory flows, compared with horses that ran without a tongue-tie. In the post hoc comparison, this effect was significant at 4 m/s, HR50, and HR90. CONCLUSION AND CLINICAL RELEVANCE: Application of a tongue-tie did not alter upper respiratory mechanics in exercising horses and may be beneficial in exercising horses with certain types of obstructive dysfunction of the upper airways. However, application of a tongue-tie does not improve upper airway mechanics in clinically normal horses.     

Plasma potassium and lactate concentrations in thoroughbred horses during exercise of varying intensity.

To investigate the effect of moderate to high intensity exercise of up to 6 min duration on plasma potassium and lactate concentrations, 6 Thoroughbred horses were studied using a treadmill at a 5 degree incline. Each test consisted of an 8-min standardised warm-up followed by an exercise bout at 8, 9, 10 or 12 m/sec. The horses were galloped at each speed for up to a maximum of 6 min or until signs of fatigue were present. The horses were then walked at 0 degree incline. Carotid arterial blood samples were taken during and after the exercise. At 8, 9 and 10 m/sec there was a general pattern of an initial rise in potassium to a peak around 1.5 min of exercise with the concentration then slowly decreasing. At 12 m/sec there was a continuous rise to a peak at the end of exercise in all horses. Immediately after exercise there was a rapid return (within 3-4 min) to the potassium concentrations recorded at the end of the warm-up period. Plasma lactate peaked around the end of exercise at all speeds. At the highest intensity of exercise the mechanisms for the re-uptake of potassium did not appear to be able to match the rate of efflux. In contrast, at less intense work loads, the rate of re-uptake appeared to be similar to or slightly greater than the rate of efflux. It is possible that a disturbance in this balance between efflux and re-uptake could result in a disturbance in normal neuromuscular function during exercise.     

Influence of different exercise regimes on the proximal hoof circumference in young Thoroughbred horses

Reasons for performing study: Most lameness in horses relates to foot problems and may be associated with changes in hoof shape, but there is a lack of information on the influence of normal exercise on hoof shape. Objectives: To investigate the effect of training on proximal hoof circumference in young Thoroughbred racehorses being prepared for racing. Methods: Thirty‐seven young Thoroughbred racehorses were included in this study. Front hoof circumference immediately below the coronary band was measured weekly with a measuring tape in all horses present at the stable. Most horses accomplished a minimum of 2 training periods at the stable separated by periods of rest on a paddock. One sample t tests were used to evaluate if the mean change per week differed from zero. To estimate the repeatability coefficient, the left proximal hoof circumference of 25 horses was measured 3 times in a random order on one day. Results: Most horses showed a similar pattern of change. The proximal hoof circumference decreased during the training periods (P<0.0001) and increased when the horse was rested (P<0.0001). The decrease of the circumference during the first training period was ?0.66 mm/week on the left and ?0.64 mm/week on the right. During the second training period, this was ?0.58 mm/week on the left and ?0.57 mm/week on the right. During the rest period, the circumference increased by 1.03 mm/week on the left and 1.12 mm/week on the right. The repeatability coefficient for the left circumference was 1.8 mm. Conclusions: Horses showed a decrease in circumference during race training that reversed when they were rested. Potential relevance: Measurement of front hoof circumference is a simple method to assess change in hoof shape. It provides an opportunity to investigate the relationships between specific training, hoof shape and soundness.     

Influence of exercise on thermographically determined surface temperatures of thoracic and pelvic limbs in horses

OBJECTIVE: To determine the amount of time required for surface temperatures of thoracic and pelvic limbs in horses to return to pre-exercise temperatures after high-speed treadmill exercise, as detected via infrared thermographic imaging. DESIGN: Prospective study. ANIMALS: 6 Thoroughbreds. PROCEDURES: All horses had been trained on and conditioned to use of a high-speed treadmill. Baseline thermographic images were obtained 3 days prior to exercise (baseline). Horses were exercised on a treadmill at a walk for 5 minutes, a slow trot (3 m/s) for 5 minutes, a trot (5 to 6 m/s) for 5 minutes, and a slow gallop (6 to 8 m/s) for 5 minutes, then back to a trot for 3 minutes, a slow trot for 3 minutes, and a walk for 3 minutes prior to stopping. Thermal images were obtained immediately after stopping exercise (0 minutes) and 5, 15, 45, and 60 minutes and 6 hours after stopping exercise. Ambient temperature surrounding each horse was recorded. RESULTS: In all regions, significant differences in surface temperatures were detected between thermograms obtained before exercise and those obtained immediately after, 5 minutes after, and 15 minutes after exercise was stopped. There were no significant differences in surface temperatures between thermograms obtained before exercise and those obtained > or = 45 minutes after exercise was stopped. CONCLUSIONS AND CLINICAL RELEVANCE: In horses, images generated via infrared thermography are not influenced by exercise-generated heat > or = 45 minutes after exercise is stopped.     

Cardiac output determination by use of lithium dilution during exercise in horses

OBJECTIVE: To compare cardiac output (CO) obtained by the lithium dilution method (LiDCO) with CO calculated from the Fick principle (FickCO), in horses maximally exercising on a high-speed treadmill. ANIMALS: 13 Thoroughbreds. PROCEDURES: In part 1 of the study, 5 horses performed a warm-up (walk, trot, and canter) and exercise test (walk, trot, canter, and gallop [90% to 100% maximum oxygen consumption [{[Formula: see text]O(2)max}]) with measurements of LiDCO and FickCO obtained simultaneously after 60 seconds at each exercise level, for a total of 7 measurements. In part 2 of the study, 8 horses performed a warm-up (walk, trot, and canter) followed by an exercise test (walk and gallop [90% to 100% [Formula: see text]O(2)max], repeated twice). Measurements of LiDCO and FickCO were obtained 60 seconds into the first walk and each gallop of the exercise tests, for a total of 3 measurements. RESULTS: Cardiac output increased significantly with increasing speeds by use of both methods. In part 1, lithium dilution significantly overestimated CO, compared with the Fick principle, during the exercise test (as both injection number and exercise intensity increased). Mean +/- SD bias was 246 +/- 264 mL of blood/min/kg in part 1 and 67 +/- 100mL of blood/kg/min in part 2. Three injections of lithium (part 2) did not result in the same degree of overestimation of LiDCO that was observed with 7 injections (part 1). CONCLUSIONS AND CLINICAL RELEVANCE: Lithium dilution may be an acceptable substitute for the Fick principle as a means to measure CO in maximally exercising client-owned horses.     

Determinants of oxygen delivery and hemoglobin saturation during incremental exercise in horses

OBJECTIVE: To determine components of the increase in oxygen consumption (VO2) and evaluate determinants of hemoglobin saturation (SO2) during incremental treadmill exercise in unfit horses. ANIMALS: 7 unfit adult mares. PROCEDURES: Horses performed 1 preliminary exercise test (EXT) and 2 experimental EXT. Arterial and mixed venous blood samples and hemodynamic measurements were taken during the last 30 seconds of each step of the GXT to measure PO2, hemoglobin concentration ([Hb]), SO2, and determinants of acid-base state (protein, electrolytes, and PCO2). RESULTS: Increased VO2 during exercise was facilitated by significant increases in cardiac output (CO), [Hb], and widening of the arteriovenous difference in O2. Arterial and venous pH, PaO2, and PvO2 decreased during exercise. Arterial PCO2, bicarbonate ([HCO3-])a, and [HCO3-] decreased significantly, whereas PVCO2 and increased. Arterial and venous sodium concentration, potassium concentration, strong ion difference, and venous lactate concentration all increased significantly during exercise. CONCLUSIONS AND CLINICAL RELEVANCE: Increases in CO, [Hb], and O2 extraction contributed equally to increased VO2 during exercise. Higher PCO2 did not provide an independent contribution to shift in the oxyhemoglobin dissociation curve (OCD) in venous blood. However, lower PaCO2 shifted the curve leftward, facilitating O2 loading. The shift of ODC resulted in minimal effect on O2 extraction because of convergence of the ODC at lower values of PO2. Decreased pH appeared responsible for the rightward shift of the ODC, which may be necessary to allow maximal O2 extraction at high blood flows achieved during exercise.     

Bronchoalveolar lavage findings in horses with exercise intolerance.

Significant differences were detected by bronchoalveolar lavage (BAL) between horses racing successfully and those showing exercise intolerance. Neutrophil percentage, haemosiderophage percentage and total bacterial numbers were significantly elevated in horses with exercise intolerance. BAL provided a more accurate indication of the incidence and extent of exercise induced pulmonary haemorrhage (EIPH) than visual inspection.     

Antibody responses of horses to equine influenza viruses during a postepizootic period in Japan.

The antibody responses to equine influenza viruses were investigated during a postepizootic period of the disease. Serum samples were collected from a total of 128 horses on three occasions during the years 1967-77. No significant increase of hemagglutination-inhibition antibody titers to subtypes 1 and 2 of equine influenza virus were detected in any of the sera tested. The maternal hemagglutination-inhibition antibody titers of foals decreased over a four month interval. A marked increase of the titers was recognized in only the equine influenza virus vaccinated horses. These findings suggest that equine influenza virus was not prevalent in the horse populations during the observation period. In such conditions, the dissemination of equine influenza viruses in the horses is discussed in relation to introduction of the disease from abroad. We also examined whether the doctrine of original antigenic sin, an immunological phenomenon recognized in human influenza, was applicable for equine influenza. However, no marked increase of hemagglutination-inhibition antibody titer to the primary infecting subtype in the 44 horses was observed after administration of the heterologous subtype vaccine.