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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 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

Summary

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° grade for 20 minutes at a speed calculated to require a power equivalent to 80% of maximal oxygen uptake (Vo 2MAX). 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.

Free access
in American Journal of Veterinary Research

Summary

Six untrained mares were subjected to incremental treadmill exercise to examine exercise-induced changes in plasma renin activity (pra) and plasma aldosterone (aldo) and plasma arginine vasopressin (avp) concentrations. Plasma renin activity, aldo and avp concentrations, and heart rate (hr) were measured at each step of an incremental maximal exercise test. Mares ran up a 6° slope on a treadmill set at an initial speed of 4 m/s. Speed was increased 1 m/s each minute until hr reached a plateau. Plasma obtained was stored at − 80 C and later was thawed, extracted, and assayed for pra and aldo and avp values by use of radioimmunoassay. Exercise caused significant increase in hr from 40 ± 2 beats/min (mean ± sem) at rest to 206 ± 4 beats/min (hr max) at speed of 9 m/s. Plasma renin activity increased from 1.9 ± 1.0 ng/ml/h at rest to a peak of 5.2 ± 1.0 ng/ml/h at 9 m/s, paralleling changes in hr. Up to treadmill speed of 9 m/s, strong linear correlations were obtained between exercise intensity (and duration) and hr (r = 0.87, P < 0.05) and pra (r = 0.93, P < 0.05). Heart rate and pra reached a plateau and did not increase when speed was increased from 9 to 10 m/s. Plasma aldo concentration increased from 48 ± 16 pg/ml at rest to 191 ± 72 pg/ml at speed of 10 m/s. Linear relation was found between exercise intensity (and duration) and aldo concentration (r = 0.97, P < 0.05). Plasma avp concentration increased from 4.0 ± 3.0 pg/ml at rest to 95 ± 5.0 pg/ml at speed of 10 m/s. The relation between avp concentration and exercise intensity (and duration) appeared to be curvilinear, and was described by an exponential function (r = 0.92, P < 0.05). These data indicate that pra and aldo and avp concentrations increase in horses during progressive treadmill exercise.

Free access
in American Journal of Veterinary Research

SUMMARY

Changes in clotting time (ct) and fibrinolytic actvity (fa) were evaluated in 6 mature, female horses during exercise. Two trials were performed on consecutive days, using a randomized crossover design. Each mare was assigned to either an exercise trial or a control trial on the first day, and to the alternate trial 24 hours later. Mares exercised for 20 minutes on a treadmill at an elevation of 2° and a velocity of 5 m/s. Venous blood samples were collected immediately before exercise, at 4, 8, 12, 16, and 20 minutes during exercise, and 15 minutes after cessation of exercise. Blood was placed into plain glass tubes for determination of CT, and into chilled, citrated tubes for determination of FA, plasminogen/plasmin complex activity (plg), one-stage prothrombin time (ospt), activated partial thromboplastin time (aptt), and antithrombin-III (at-III) activity. There were significant differences (P < 0.05) between the control and exercise groups for ct, fa, and plg. During exercise, clotting time decreased from 21.5 ± 1.6 minutes to 9.9 ± 1.6 minutes (mean ± sd; P < 0.05), without significant changes in ospt, aptt, or at-III. Fibrinolytic activity and plg increased (P < 0.05) during exercise. Changes in ct, fa, and plg were significant at 4 minutes of exercise, remained altered until the end of exercise, and returned to baseline values by 45 minutes of recovery. Clotting time, ospt, aptt, fa, at-III, and plg did not change (P > 0.05) during control trials.

Free access
in American Journal of Veterinary Research

Abstract

Objective

To compare exercise-induced immune modulation in young and older horses.

Animals

6 young and 6 aged horses that were vaccinated against equine influenza virus.

Procedure

Venous blood samples were collected for immunologic assessment before and immediately after exercise at targeted heart rates and after exercise for determination of plasma lactate and cortisol concentrations. Mononuclear cells were assayed for lymphoproliferative responses and incubated with interieukin-2 (IL-2) to induce lymphokine-activated killer (LAK) cells. Antibodies to equine influenza virus were measured.

Results

Older horses had significantly lower proliferative responses to mitogens than younger horses prior to exercise. Exercise caused a significant decrease in lymphoproliferative response of younger horses, but not of older horses. Activity of LAK cells increased slightly with exercise intensity in younger horses. Cortisol concentrations increased in both groups after exercise; younger horses had higher concentrations after exercise at heart rates of 180 and 200 beats/min than those of older horses. Plasma lactate concentrations increased with exercise intensity but there were no differences between older and younger horses. Older horses had lower antibody titers to equine influenza virus than younger horses. Exercise did not affect antibody titers.

Conclusion

Although lymphoproliferative responses and antibody titers of older horses were less than those of younger horses, older horses were more resistant to exercise-induced changes in immune function, possibly because of lower cortisol concentrations.

Clinical Relevance

Stress and aging are known to affect immune function. Older horses had reduced immune function, but were more resistant to exercise-induced immune suppression than younger horses. (Am J Vet Res 1999;60:643–647)

Free access
in American Journal of Veterinary Research

Abstract

Objective—To describe neuroendocrine responses that develop in dogs subjected to prolonged periods of ventricular pacing.

Animals—14 adult male hound-type dogs.

Procedure—Samples were obtained and neuroendocrine responses measured before (baseline) and after 3 periods of ventricular pacing. A pacemaker was used to induce heart rates of 180, 200, and 220 beats/min (BPM). Each heart rate was maintained for 3 weeks before increasing to the next rate. Atrial natriuretic peptide, antidiuretic hormone, aldosterone, norepinephrine, epinephrine, and dopamine concentrations and plasma renin activity were measured. Severity of left ventricular compromise was estimated.

Results—Shortening fraction decreased significantly with increasing heart rates (mean ± SE, 35.5 ± 1.4, 25.0 ± 1.4, 19.5 ± 1.9, and 12.2 ± 2.3 for baseline, 180 BPM, 200 BPM, and 220 BPM, respectively). Atrial natriuretic peptide concentrations increased significantly at 180 BPM (44.1 ± 3.0 pg/mL) and 200 BPM (54.8 ± 5.5 pg/mL), compared with baseline concentration (36.8 ± 2.6 pg/mL). Dopamine concentration increased significantly at 200 BPM (70.4 ± 10.4 pg/mL), compared with baseline concentration (44.2 ± 7.3 pg/mL). Norepinephrine concentrations increased significantly from baseline concentration (451 ± 46.2 pg/mL) to 678 ± 69.8, 856 ± 99.6, and 1,003 ± 267.6 pg/mL at 180, 200, and 220 BPM, respectively.

Conclusions and Clinical Relevance—Dogs subjected to ventricular pacing for 9 weeks developed neuroendocrine responses similar to those that develop in humans with more chronic heart failure and, except for epinephrine concentrations, similar to those for dogs subjected to ventricular pacing for < 6 weeks. (Am J Vet Res 2002;63:1413–1417)

Full access
in American Journal of Veterinary Research