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Abstract

Objective

To quantify total fluid loss in sweat of Thoroughbreds during > 3 hours of low-intensity exercise in controlled conditions and to calculate and compare estimated ion losses in sweat, according to 3 methods.

Animals

6 exercise-trained Thoroughbreds.

Procedure

Fluid and ion losses in sweat were measured in 6 horses exercising at 40% of the speed that elicited maximum oxygen consumption for 45 km. Horses were given a 15-minute rest period at the end of three 15-km exercise phases. Horses completed 2 exercise trials. Ion losses in sweat were calculated, using measurements of local sweating rate and sweat ion composition (SWT), change in net exchangeable cation content (CAT), and change in extracellular ion content (PLAS) derived from plasma total solids and ion concentrations.

Results

Measurement of SWT revealed a mean (± SEM) fluid loss in sweat during 45 km of exercise of 27.5 ± 1.6 L. Total ion loss in sweat was approximately 241 g or 7.8 mol with higher sodium losses in the second and third phases of exercise compared with the first phase. Losses of sodium and potassium calculated by SWT or CAT were not significantly different from each other, whereas losses of these ions as determined by PLAS were significantly lower.

Conclusions and Clinical Relevance

Calculation of ion losses from a mean whole body sweating rate extrapolated from either local sweating rate and sweat ion composition or from change in net exchangeable cation content provide similar results, whereas ion losses determined by changes in extracellular ion content derived from plasma total solids and ion concentration results in underestimation of actual losses. (Am J Vet Res 1999;60:1248–1254)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To compare dew-point hygrometry, direct sweat collection, and measurement of body water loss as methods for determination of sweating rate (SR) in exercising horses.

Animals

6 exercise-trained Thoroughbreds.

Procedure

SR was measured in 6 horses exercising at 40% of the speed that elicited maximum oxygen consumption for 45 km, with a 15-minute rest at the end of each 15-km phase. Each horse completed 2 exercise trials. Dew-point hygrometry, as a method of local SR determination, was validated in vitro by measurement of rate of evaporative water loss. During exercise, local SR was determined every 10 minutes by the following 2 methods: (1) dew-point hygrometry on the neck and lateral area of the thorax, and (2) on the basis of the volume of sweat collected from a sealed plastic pouch attached to the lateral area of the thorax. Mean whole body SR was calculated from total body water loss incurred during exercise.

Results

Evaporation rate measured by use of dewpoint hygrometry was significantly correlated (r 2 = 0.92) with the actual rate of evaporative water loss. There was a similar pattern of change in SR measured by dew-point hygrometry on the neck and lateral area of the thorax during exercise, with a significantly higher SR on the neck. The SR measured on the thorax by direct sweat collection and by dew-point hygrometry were of similar magnitude. Mean whole body SR calculated from total body water loss was not significantly different from mean whole body SR estimated from direct sweat collection or dew-point hygrometry measurements on the thorax.

Conclusions

Dew-point hygrometry and direct sweat collection are useful methods for determination of local SR in horses during prolonged, steady-state exercise in moderate ambient conditions. Both methods of local SR determination provide an accurate estimate of whole body SR. (Am J Vet Res 1997;58:175–181)

Free access
in American Journal of Veterinary Research

Abstract

Objective—To investigate the effects of sodium citrate, low molecular weight heparin (LMWH), and prostaglandin E1 (PGE1) on aggregation, fibrinogen binding, and enumeration of equine platelets. Sample Population—Blood samples obtained from 4 Thoroughbreds.

Sample Population—Blood samples obtained from 4 Thoroughbreds.

Procedure—Blood was collected into syringes in the ratio of 9 parts blood:1 part anticoagulant. Anticoagulants used were sodium citrate, LMWH, sodium citrate and LMWH, or 300 nM PGE1/ml of anticoagulant. Platelet aggregation in response to ADP, collagen, and PGE1 was assessed, using optical aggregometry. Platelet activation was evaluated, using flow cytometry, to detect binding of fluorescein- conjugated anti-human fibrinogen antibody. Plasma concentration of ionized calcium was measured, using an ion-selective electrode.

Results—Number of platelets (mean ± SEM) in samples containing LMWH (109.5 ± 11.3 × 103 cells/µl) was significantly less than the number in samples containing sodium citrate (187.3 ± 30.3 × 103 cells/µl). Increasing concentrations of sodium citrate resulted in reductions in platelet aggregation and plasma concentration of ionized calcium. Addition of PGE1 prior to addition of an agonist inhibited platelet aggregation in a concentration-dependent manner, whereas addition of PGE1 4 minutes after addition of ADP resulted in partial reversal of aggregation and fibrinogen binding.

Conclusion and Clinical Relevance—A high concentration of sodium citrate in blood samples decreases plasma concentration of ionized calcium, resulting in reduced platelet aggregation and fibrinogen binding. Platelets tend to clump in samples collected into LMWH, precluding its use as an anticoagulant. Platelet aggregation and fibrinogen binding can be reversed by PGE1, which may result in underestimation of platelet activation. (Am J Vet Res 2001; 62:547–554)

Full access
in American Journal of Veterinary Research

Abstract

Objectives—To assess safety and determine effects of IV administration of formaldehyde on hemostatic variables in healthy horses.

Animals—7 healthy adult horses.

Procedure—Clinical signs and results of CBC, serum biochemical analyses, and coagulation testing including template bleeding time (TBT) and activated clotting time (ACT) were compared in horses given a dose of 0.37% formaldehyde or lactated Ringer’s solution (LRS), IV, in a 2-way crossover design. In a subsequent experiment, horses received an infusion of 0.74% formaldehyde or LRS. In another experiment, horses were treated with aspirin to impair platelet responses prior to infusion of formaldehyde or LRS.

Results—Significant differences were not detected in any variable measured between horses when given formaldehyde or any other treatment. Infusion of higher doses of formaldehyde resulted in adverse effects including muscle fasciculations, tachycardia, tachypnea, serous ocular and nasal discharge, agitation, and restlessness.

Conclusions and Clinical Relevance—Intravenous infusion of formaldehyde at doses that do not induce adverse reactions did not have a detectable effect on measured hemostatic variables in healthy horses. (Am J Vet Res 2000;61:1191–1196)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To investigate the potential use of fluorescent- labeled annexin V, anti-human fibrinogen antibody, and anti-human thrombospondin antibody for detection of the activation of equine platelets by use of flow cytometry.

Sample Population—Platelets obtained from 6 Thoroughbreds.

Procedure—Flow cytometry was used to assess platelet activation as indicated by detection of binding of fluorescent-labeled annexin V, anti-human fibrinogen antibody, and anti-thrombospondin antibody to unactivated and ADP-, collagen-, platelet activating factor (PAF)-, and A23187-activated equine platelets. Human platelets were used as control samples. Determination of 14C-serotonin uptake and release was used to assess the extent of platelet secretion.

Results—Anti-human thrombospondin antibody failed to bind to equine platelets. Annexin V bound to platelets activated with PAF or A23187 when platelets had undergone secretion. Anti-human fibrinogen antibody bound to ADP-, PAF-, and A23817- activated platelets, but binding was not dependent on platelet secretion. The extent of binding of anti-fibrinogen antibody was less in equine platelets, compared with that for human platelets, despite maximal stimulation.

Conclusions and Clinical Relevance—Activation of equine platelets can be detected by use of fluorescent- labeled annexin V and anti-human fibrinogen antibody but not by use of anti-human thrombospondin antibody. These flow cytometric techniques have the potential for detection of in vivo platelet activation in horses at risk of developing thrombotic disorders. (Am J Vet Res 2002;63:513–519)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To investigate the effects of formaldehyde fixation on equine platelets using flow cytometric methods to evaluate markers of platelet activation.

Sample Population—Blood samples from 6 Thoroughbreds.

Procedure—The degree of fluorescence associated with binding of fluorescein isothiocyanate (FITC)-conjugated anti-human fibrinogen antibody and FITCannexin V in unactivated and adenosine diphosphate (ADP)-, platelet activating factor (PAF)-, and A23187- activated platelet samples in unfixed and 0.5, 1.0, and 2.0% formaldehyde-fixed samples was assessed by use of flow cytometry.

Results—In samples incubated with FITC-anti-human fibrinogen antibody prior to fixation, addition of 2.0% formaldehyde resulted in a 30% increase in total fluorescence in ADP- and PAF-activated samples and a 60% increase in A23187-activated samples. Fixation for 24 hours prior to addition of antibody resulted in reduced fluorescence of samples containing antihuman fibrinogen antibody for all 3 concentrations of formaldehyde in PAF-activated samples. The addition of all 3 concentrations of formaldehyde after incubation with FITC-annexin V resulted in significant increases in fluorescence in unactivated and activated platelet samples. As length of fixation time increased, there was a gradual increase in fluorescence that was significant at 24 hours.

Conclusion and Clinical Relevance—Because fixation with 2.0% formaldehyde results in significant changes in fluorescence in activated platelet samples containing anti-fibrinogen antibody, lower concentrations of formaldehyde should be used to fix equine platelet samples. Formaldehyde-fixed platelet samples should be analyzed within 12 hours of fixation to avoid artifactual increases in fluorescence. Fixation of samples containing FITC-annexin V should be avoided because of significant increases in fluorescence that may interfere with interpretation of results. (Am J Vet Res 2002;63:840–844)

Full access
in American Journal of Veterinary Research

Abstract

Objectives—To establish maximum oxygen consumption (O2max) in ponies of different body weights, characterize the effects of training of short duration on O2max, and compare these effects to those of similarly trained Thoroughbreds.

Animals—5 small ponies, 4 mid-sized ponies, and 6 Thoroughbreds.

Procedure—All horses were trained for 4 weeks. Horses were trained every other day for 10 minutes on a 10% incline at a combination of speeds equated with 40, 60, 80, and 100% of O2max. At the beginning and end of the training program, each horse performed a standard incremental exercise test in which O2max was determined. Cardiac output (), stroke volume (SV), and arteriovenous oxygen content difference (C [a-v] O2) were measured in the 2 groups of ponies but not in the Thoroughbreds.

Results—Prior to training, mean O2max for each group was 82.6 ± 2.9, 97.4 ± 13.2, and 130.6 ± 10.4 ml/kg/min, respectively. Following training, mean O2max increased to 92.3 ± 6.0, 107.8 ± 12.8, and 142.9 ± 10.7 ml/kg/min. Improvement in O2max was significant in all 3 groups. For the 2 groups of ponies, this improvement was mediated by an increase in ; this variable was not measured in the Thoroughbreds. Body weight decreased significantly in the Thoroughbreds but not in the ponies.

Conclusions and Clinical Relevance—Ponies have a lower O2max than Thoroughbreds, and larger ponies have a greater O2max than smaller ponies. Although mass-specific O2max changed similarly in all groups, response to training may have differed between Thoroughbreds and ponies, because there were different effects on body weight. (Am J Vet Res 2000; 61:986–991)

Full access
in American Journal of Veterinary Research