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Abstract

Objective—To characterize age-associated changes in lymphocyte population subsets and immunoglobulin isotypes.

Animals—30 healthy young light-breed horses (5 to 12 years old) and 30 healthy aged light-breed horses (> 20 years old).

Procedure—Lymphocyte subset populations were identified, using monoclonal antibodies to cell surface markers CD5, CD4, CD8, and IgG. Subset populations were quantitated by use of flow cytometric analysis of antibody-stained cells. Serum immunoglobulin concentration was determined using single radial immunodiffusion.

Results—Absolute cell counts of total lymphocytes, T cells, CD4+ and CD8+ T cells, and B cells were decreased in aged horses, compared with young horses. There was a significant decrease in the percentage of CD8+ cells and an increase in the CD4+-to- CD8+ cell ratio in the aged population, compared with young horses. However, serum concentration of IgG, IgG(T), IgM, or IgA did not differ with age.

Conclusions and Clinical Relevance—In horses, total lymphocyte count and lymphocyte subset cell counts decrease with age. Age-matched control values are necessary for optimal evaluation of hematologic variables in aged horses. The decrease in lymphocyte subset cell counts in healthy aged horses mimics that seen in other species and may contribute to an age-associated decrease in immunocompetency. ( Am J Vet Res 2001;62:1413–1417)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine an infusion rate of butorphanol tartrate in horses that would maintain therapeutic plasma drug concentrations while minimizing development of adverse behavioral and gastrointestinal tract effects.

Animals—10 healthy adult horses.

Procedure—Plasma butorphanol concentrations were determined by use of high-performance liquid chromatography following administration of butorphanol by single IV injection (0.1 to 0.13 mg/kg of body weight) or continuous IV infusion (loading dose, 17.8 µg/kg; infusion dosage, 23.7 µg/kg/h for 24 hours). Pharmacokinetic variables were calculated, and changes in physical examination data, gastrointestinal tract transit time, and behavior were determined over time.

Results—A single IV injection of butorphanol was associated with adverse behavioral and gastrointestinal tract effects including ataxia, decreased borborygmi, and decreased defecation. Elimination half-life of butorphanol was brief (44.37 minutes). Adverse gastrointestinal tract effects were less apparent during continuous 24-hour infusion of butorphanol at a dosage that resulted in a mean plasma concentration of 29 ng/ml, compared with effects after a single IV injection. No adverse behavioral effects were observed during or after continuous infusion.

Conclusions and Clinical Relevance—Continuous IV infusion of butorphanol for 24 hours maintained plasma butorphanol concentrations within a range associated with analgesia. Adverse behavioral and gastrointestinal tract effects were minimized during infusion, compared with a single injection of butorphanol. Continuous infusion of butorphanol may be a useful treatment to induce analgesia in horses. (Am J Vet Res 2001;62:183–189)

Full access
in American Journal of Veterinary Research

Abstract

OBJECTIVE To identify potential risk factors for digit injuries in dogs training and competing in agility events.

DESIGN Internet-based, retrospective, cross-sectional survey.

ANIMALS 1,081 dogs training or competing in agility events.

PROCEDURES Data were collected for eligible animals via retrospective surveys distributed electronically to handlers of dogs participating in agility-related activities. Variables evaluated included demographic (handlers) and signalment (dogs) information, physical characteristics of dogs, and injury characteristics. A separate survey of dogs competing in similar agility-related activities but without digit injuries was also administered. Multivariable logistic regression was used to develop a model for assessment of risk factors.

RESULTS Data were collected from 207 agility dogs with digit injuries and 874 agility dogs without digit injuries. Factors associated with significantly increased odds of injury included Border Collie breed (OR, 2.3; 95% confidence interval [CI], 1.5 to 3.3), long nails (OR, 2.4; 95% CI, 1.3 to 4.5), absence of front dewclaws (OR, 1.9; 95% CI, 1.3 to 2.6), and greater weight-to-height ratio (OR, 1.5; 95% CI, 1.1 to 2.0). Odds of injury decreased with increasing age of the dog (OR, 0.8; 95% CI, 0.76 to 0.86).

CONCLUSIONS AND CLINICAL RELEVANCE Results should be cautiously interpreted because of potential respondent and recall bias and lack of review of medical records. Nevertheless, results suggested that retaining healthy dewclaws, maintaining lean body mass, and trimming nails short for training and competition may decrease the likelihood of digit injuries. Research to investigate training practices, obstacle construction specifcations, and surface considerations for dogs competing in agility activities is indicated.

Restricted access
in Journal of the American Veterinary Medical Association
in Journal of the American Veterinary Medical Association

Abstract

OBJECTIVE To determine the plasma pharmacokinetics and safety of 1% diclofenac sodium cream applied topically to neonatal foals every 12 hours for 7 days.

ANIMALS Twelve 2- to 14-day old healthy Arabian and Arabian-pony cross neonatal foals.

PROCEDURES A 1.27-cm strip of cream containing 7.3 mg of diclofenac sodium (n = 6 foals) or an equivalent amount of placebo cream (6 foals) was applied topically to a 5-cm square of shaved skin over the anterolateral aspect of the left tarsometatarsal region every 12 hours for 7 days. Physical examination, CBC, serum biochemistry, urinalysis, gastric endoscopy, and ultrasonographic examination of the kidneys and right dorsal colon were performed before and after cream application. Venous blood samples were collected at predefined intervals following application of the diclofenac cream, and plasma diclofenac concentrations were determined by liquid chromatography–mass spectrometry.

RESULTS No foal developed any adverse effects attributed to diclofenac application, and no significant differences in values of evaluated variables were identified between treatment groups. Plasma diclofenac concentrations peaked rapidly following application of the diclofenac cream, reaching a maximum of < 1 ng/mL within 2 hours, and declined rapidly after application ceased.

CONCLUSIONS AND CLINICAL RELEVANCE Topical application of the 1% diclofenac sodium cream to foals as described appeared safe, and low plasma concentrations of diclofenac suggested minimal systemic absorption. Practitioners may consider use of this medication to treat focal areas of pain and inflammation in neonatal foals.

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 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 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