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Abstract

Objective

To determine whether body temperature of horses exercised in hot, humid conditions and then repetitively washed with cold water will decrease more rapidly than that of horses that are not washed, and to determine whether washing with cold water has deleterious effects on horses.

Animals

5 physically fit Thoroughbred mares, 3 to 10 years old.

Procedures

Horses were exercised on a high-speed treadmill in hot (31.1 ± 0.3 C), humid (relative humidity, 77.7 ± 2%) conditions. Exercise was terminated when pulmonary artery temperature reached 41.5 C. Values for pulmonary artery, rectal, and left gluteal muscle temperatures were compared throughout a 30-minute recovery period after exercise during which horses stood quietly (passive cooling) or were cooled (active cooling) by repeated applications of cold (15.6 ± 0.6 C) water.

Results

Pulmonary artery temperature was significantly less for actively cooled horses, compared with passively cooled horses 4 minutes into the recovery period. Left gluteal muscle temperature decreased significantly in actively cooled, but not passively cooled, horses during the recovery period. Heart rate and rectal temperature were significantly less for actively cooled horses by 15 minutes of the recovery period. Cooling technique did not effect hydration status, muscle health, or serum electrolyte concentrations. Active cooling did not cause obvious adverse effects.

Conclusion and Clinical Relevance

Active cooling by washing with cold water is a safe, effective means for facilitating heat dissipation of horses after exercise in a hot, humid environment. (Am J Vet Res 1999;60:299–305)

Free access
in American Journal of Veterinary Research

Abstract

Objective—To determine the effect of administration of commercially available sodium bicarbonate (NaHCO3) on carbon 13 (13C) isotopic enrichment of carbon dioxide (CO2) in serum of horses.

Animals—7 healthy Thoroughbreds.

Procedure—Sodium bicarbonate (450 g) was administered via nasogastric intubation to horses. Horses had been fed a diet obtained from the same source and had access to water from the same source for 3 months before the study. Blood samples were collected immediately before and at 2, 4, 6, and 24 hours after administration of NaHCO3. The concentration of total CO2 in serum was measured by use of a commercial analyzer. The 13C enrichment of bicarbonate in serum was estimated by measurement of 13C enrichment of CO2 released by acidification of the serum. The 13C enrichment of commercially available NaHCO3 was also determined and compared with that of CO2 in serum of horses before administration of NaHCO3.

Results—Commercially available NaHCO3 had a 13C enrichment significantly different from that of carbon dioxide in serum of horses before treatment. Administration of NaHCO3 increased the concentration of total CO2 from pretreatment values. The 13C enrichment of CO2 in serum was only transiently and minimally affected after administration of NaHCO3.

Conclusions and Clinical Relevance—Administration of NaHCO3 was not detected by measuring 13C enrichment of CO2 in serum of horses. ( Am J Vet Res 2004;65:307–310)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine components of the increase in oxygen consumption (O2) 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 acidbase state (protein, electrolytes, and PCO2).

Results—Increased O2 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]v 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 O2 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. (Am J Vet Res 2000;61:1325–1332)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To evaluate plasma epinephrine and norepinephrine concentrations and serum cortisol concentration in horses with colic and assess the relationship of these variables with clinical signs, routinely measured clinicopathologic variables, and outcome in affected horses.

Design—Prospective observational study.

Animals—35 horses with colic.

Procedure—Blood samples were collected within 30 minutes of arrival at the veterinary hospital from horses referred because of colic. Plasma and serum samples were analyzed for cortisol, epinephrine, norepinephrine, lactate, and electrolyte concentrations and acid-base variables. Heart rate at admission and outcome (survival or nonsurvival) were recorded. Univariate logistic regression was used to calculate crude (unadjusted) odds ratios and 95% confidence intervals.

Results—Of the 35 horses with colic, 26 survived. Higher plasma epinephrine, plasma lactate, and serum cortisol concentrations were significantly associated with increased risk of nonsurvival, but plasma norepinephrine concentration was not associated with outcome. Plasma epinephrine concentration was significantly correlated with heart rate (r = 0.68), plasma lactate concentration (r = 0.87), blood pH (r = –0.83), anion gap (r = 0.74), and base excess (r = –0.81).

Conclusions and Clinical Relevance—The risk of death appears to be greater in colic-affected horses with high circulating concentrations of epinephrine and cortisol. The correlation of epinephrine with other biochemical markers of illness severity and with heart rate indicates that the degree of sympathetic activation in horses with colic can be inferred from routinely measured variables. (J Am Vet Med Assoc 2005;227:276–280)

Full access
in Journal of the American Veterinary Medical Association

SUMMARY

The cardiovascular effects of xylazine and detomidine in horses were studied. Six horses were given each of the following 5 treatments, at 1-week intervals: xylazine, 1.1 mg/kg, iv; xylazine, 2.2 mg/kg, im; detomidine, 0.01 mg/ kg, iv; detomidine, 0.02 mg/kg, iv; and detomidine, 0,04 mg/kg, im. All treatments resulted in significantly decreased heart rate, increased incidence of atrioventricular block, and decreased cardiac output and cardiac index; cardiac output and cardiac index were lowest following iv administration of 0.02 mg of detomidine/kg. Mean arterial pressure was significantly reduced for various periods with all treatments; however, iv administration of 0.02 nig of detomidine/kg caused hypertension initially. Systemic vascular resistance was increased by all treatments. Indices of ventricular contractility and relaxation, + dP/dt and − dP/dt, were significantly depressed by all treatments. Significant changes were not detected in stroke volume or ejection fraction. The pcv was significantly reduced by all treatments. Respiratoiy rate was significantly decreased with all treatments, but arterial carbon dioxide tension did not change. Arterial oxygen tension was significantly decreased briefly with the 3 iv treatments only.

Free access
in American Journal of Veterinary Research

Abstract

Objective—To determine the effect of endurance training on QRS duration, QRS-wave amplitude, and QT interval.

Animals—100 sled dogs in Alaska.

Procedure—Dogs were examined in early September (before training) and late March (after training). During the interim, dogs trained by pulling a sled with a musher (mean, 20 km/d). Standard and signal-averaged ECG were obtained before and after training.

Results—Endurance training significantly increased mean QRS duration by 4.4 milliseconds for standard ECG (mean ± SEM; 62.3 ± 0.7 to 66.7 ± 0.6 milliseconds) and 4.3 milliseconds for signal-averaged ECG (51.5 ± 0.7 to 55.8 ± 0.6 milliseconds) without changing body weight. Increase in QRS duration corresponded to a calculated increase in heart weight (standard ECG, 23%; signal-averaged ECG, 27%). Signal-averaged QRS duration was correlated with echocardiographically determined left ventricular diastolic diameter for the X orthogonal lead (r = +0.41), Y orthogonal lead (r = +0.33), and vector (r = +0.35). Training also increased QT interval (234 ± 2 to 249 ± 2 milliseconds) and R-wave amplitude in leads II and rV2, increased peak-to-peak voltage and S-wave amplitude in the Y orthogonal lead, and decreased Q-wave amplitude in the Y orthogonal lead.

Conclusions and Clinical Relevance—Electrocardiographic changes reflected physiologic cardiac hypertrophy in these canine athletes in response to repetitive endurance exercise. The QRS duration increases in response to endurance exercise training and, therefore, may be of use in predicting performance in endurance activities. (Am J Vet Res 2000;61:582–588)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To compare effects of low and high intensity warm-up exercise on oxygen consumption (O2) and carbon dioxide production (CO2 ) in horses. Animals—6 moderately conditioned adult Standardbreds.

Procedures—Horses ran for 2 minutes at 115% of maximum oxygen consumption (O2max), 5 minutes after each of the following periods: no warm-up (NoWU); 10 minutes at 50% of O2max (LoWU); or 7 minutes at 50% O2max followed by 45-second intervals at 80, 90, and 100% O2max (HiWU). Oxygen consumption and CO2 were measured during exercise, and kinetics of O2 and CO2 were calculated. Accumulated O2 deficit was also calculated.

Results—For both warm-up trials, the time constant for the rapid exponential increase in O2 was 30% lower than for NoWU. Similarly, the rate of increase in CO2 was 23% faster in LoWU and HiWU than in NoWU. Peak values for O2 achieved during the highspeed test were not significantly different among trials (LoWU, 150.2 ± 3.2 ml/kg/min; HiWU, 151.2 ± 4.2 ml/kg/min; NoWU, 145.1 ± 4.1 ml/kg/min). However, accumulated O2 deficit (ml of O2 equivalents/kg) was significantly lower during LoWU (65.3 ± 5.1) and HiWU (63.4 ± 3.9) than during NoWU (82.1 ± 7.3).

Conclusions and Clinical Relevance—Both the lowand high-intensity warm-up, completed 5 minutes before the start of high-intensity exercise, accelerated the kinetics of O2 and CO2 and decreased accumulated O2 deficit during 2 minutes of intense exertion in horses that were moderately conditioned. (Am J Vet Res 2000;61:638–645)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine the effect of a tongue-tie on upper airway mechanics in clinically normal horses exercising on a treadmill following sternothyrohyoid myectomy.

Animals—6 Standardbreds.

Procedure—Upper airway mechanics were measured with horses exercising on a treadmill at 5, 8, and 10 m/s 4 weeks after a sternothyrohyoid myectomy was performed. Pharyngeal and tracheal inspiratory and expiratory pressures were measured by use of transnasal pharyngeal and tracheal catheters connected to differential pressure transducers. Horses were fitted with a facemask and airflow was measured by use of a pneumotachograph. Horses underwent a standardized exercise protocol on a treadmill at 5, 8, and 10 m/s with and without a tongue-tie in a randomized cross-over design. Inspiratory and expiratory airflow, tracheal pressure, and pharyngeal pressure were measured, and inspiratory and expiratory resistances were calculated.

Results—We were unable to detect an effect of a tongue-tie on any of the respiratory variables measured.

Conclusions and Clinical Relevance—Results indicate that a tongue-tie does not alter upper airway mechanics following sternothyrohyoid myectomy in clinically normal horses during exercise. (Am J Vet Res 2001;62:779–782)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To characterize insulin-sensitive glucose-transporter (GLUT-4) protein in equine tissues and determine effects of exercise and glucose administration on content of GLUT-4 protein in equine skeletal muscle.

Sample Population—Tissue samples from 9 horses.

Procedure—Western blot analyses were performed on crude membrane preparations of equine tissues to characterize GLUT-4. In a crossover, randomized study, horses were strenuously exercised for 3 consecutive days and then administered 13.5% glucose or isotonic saline (0.9% NaCl; control) solution, IV, at similar infusion rates for 12.1 hours. Samples were collected from the middle gluteal muscle before and after exercise and 10.1 hours after completion of an infusion and used for measurements of glycogen concentration and total content of GLUT-4 protein.

Results—Immunoblot analyses detected specifically immunoreactive bands for GLUT-4 in insulin-sensitive tissues. Content of GLUT-4 protein in skeletal muscle increased significantly by 27.3 and 12.3% 22.2 hours after exercise for control and glucose groups, respectively. Intravenous infusion of glucose resulted in a significantly higher rate of glycogenesis, compared with results for the control group (mean ± SD, 3.98 ± 0.61 and 1.47 ± 0.20 mmol/kg/h, respectively). Despite enhanced glycogenesis, we did not detect an increase in content of GLUT-4 protein after glucose infusion, compared with values after exercise.

Conclusions and Clinical Relevance—GLUT-4 protein was expressed in equine skeletal and cardiac muscles. Exercise increased total content of GLUT-4 protein in skeletal muscle, and replenishment of muscle glycogen stores after glucose infusion attenuated the exercise-induced increase in the content of GLUT-4 protein in equine skeletal muscle. (Am J Vet Res 2003;64:1500–1506)

Full access
in American Journal of Veterinary Research