Objective—To characterize age-associated changes
in lymphocyte population subsets and immunoglobulin
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)
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
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
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)
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
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
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
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)
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
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
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
Sample Population—Blood samples obtained from
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;
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
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,
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)
Objective—To compare the analgesic efficacy of administration of butorphanol tartrate, phenylbutazone, or both drugs in combination in colts undergoing routine castration.
Design—Randomized controlled clinical trial.
Animals—36 client-owned colts.
Procedures—Horses received treatment with butorphanol alone (0.05 mg/kg [0.023 mg/lb], IM, prior to surgery and then q 4 h for 24 hours), phenylbutazone alone (4.4 mg/kg [2.0 mg/lb], IV, prior to surgery and then 2.2 mg/kg [1.0 mg/lb], PO, q 12 h for 3 days), or butorphanol and phenylbutazone at the aforementioned dosages (12 horses/group). For single-drug–treated horses, appropriate placebos were administered to balance treatment protocols among groups. All horses were anesthetized, and lidocaine hydrochloride was injected into each testis. Physical and physiological variables, plasma cortisol concentration, body weight, and water consumption were assessed before and at intervals after surgery, and induction of and recovery from anesthesia were subjectively characterized. Observers assessed signs of pain by use of a visual analogue scale and a numerical rating scale.
Results—Significant changes in gastrointestinal sounds, fecal output, and plasma cortisol concentrations were evident in each treatment group over time, compared with preoperative values. At any time point, assessed variables and signs of pain did not differ significantly among groups, although the duration of recumbency after surgery was longest for the butorphanol-phenylbutazone–treated horses.
Conclusions and Clinical Relevance—With intratesticular injections of lidocaine, administration of butorphanol to anesthetized young horses undergoing routine castration had the same apparent analgesic effect as phenylbutazone treatment. Combined butorphanolphenylbutazone treatment was not apparently superior to either drug used alone.
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.
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.