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Abstract

Objective—To determine plasma endotoxin concentration in horses competing in a 48-, 83-, or 159-km endurance race and its importance with regard to physical, hematologic, or serum and plasma biochemical variables.

Animals—83 horses.

Procedure—Weight and rectal temperature measurements and blood samples were obtained before, during, and after exercise. Blood samples were analyzed for plasma endotoxin concentration; serum antiendotoxin antibody titers; thromboxane B2 (TxB2) and 6- keto-prostaglandin F (PGF) concentrations; tumor necrosis factor alpha (TNFα) and interleukin-6 (IL-6) activities; WBC, plasma protein, lactate, serum electrolyte, and calcium concentrations; PCV; and creatine kinase activity.

Results—Detection of plasma endotoxin increased during exercise for horses competing at all distances but occurred more frequently in the 48- and 83-km groups. Plasma lactate concentration was significantly greater when endotoxin was concurrently detected. Endotoxin in plasma was not significantly associated with success of race completion. Plasma TxB2 and PGF concentrations and serum IL-6 activity significantly increased with exercise. Horses that had an excellent fitness level (as perceived by their owners) had greater decreases in serum antiendotoxin antibody titers during exercise than did horses perceived as less fit. In horses with better finish times, TxB2 and PGF concentrations were significantly greater and TNFα activity was significantly less than that of slower horses.

Conclusions and Clinical Relevance—Endotoxemia developed during endurance racing, but was significantly correlated with increased plasma lactate concentration and not with other variables indicative of endotoxemia. Plasma TxB2 and PGF concentrations and serum TNFα activity may be associated with performance success. (Am J Vet Res 2003;64:754–761)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To compare physiologic, hematologic, and selected serum and plasma biochemical variables obtained from horses competing in 48-, 83-, or 159- km endurance rides before competition and at the same cumulative distance points.

Animals—83 horses.

Procedure—Weight and rectal temperature measurements and blood samples were obtained from horses before, during, and after 1 of 3 rides conducted on the same day. Plasma protein (PP), lactate, WBC, serum electrolyte, and calcium concentrations; PCV; and creatine kinase (CK) activity were determined. Assessments were made to determine whether any differences among groups, with respect to total distance competed, could be explained by differences in lap speed or conditioning and to investigate the effect of time in transit or on-site prior to competition on results of blood analyses or competition outcome.

Results—Horses in the 159-km distance group had the lowest preride serum sodium, chloride, bicarbonate, and calcium concentrations. As hours in transit increased, preride PP concentration was significantly greater; serum sodium, chloride, and bicarbonate concentrations were lower; CK activity at 159 km was greater; and horses were more likely to be eliminated. The preride sodium was significantly greater in horses that completed the ride, compared with those eliminated.

Conclusions and Clinical Relevance—Among distance groups, distance ridden, speed, level of fitness, and years of experience of horses had little effect on the variables examined. Electrolyte and water supplementation and earlier arrival at the event may be beneficial for horses that are transported long distances to endurance competition. (Am J Vet Res 2003;64:746–753)

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in American Journal of Veterinary Research

Abstract

Objective—To determine the pharmacokinetics of azithromycin and its concentration in body fluids and bronchoalveolar lavage cells in foals.

Animals—6 healthy 6- to 10-week-old foals.

Procedure—Azithromycin (10 mg/kg of body weight) was administered to each foal via IV and intragastric (IG) routes in a crossover design. After the first IG dose, 4 additional IG doses were administered at 24-hour intervals. A microbiologic assay was used to measure azithromycin concentrations in serum, peritoneal fluid, synovial fluid, pulmonary epithelial lining fluid (PELF), and bronchoalveolar (BAL) cells.

Results—Azithromycin elimination half-life was 20.3 hours, body clearance was 10.4 ml/min·kg, and apparent volume of distribution at steady state was 18.6 L/kg. After IG administration, time to peak serum concentration was 1.8 hours and bioavailability was 56%. After repeated IG administration, peak serum concentration was 0.63 ± 0.10 µg/ml. Peritoneal and synovial fluid concentrations were similar to serum concentrations. Bronchoalveolar cell and PELF concentrations were 15- to 170-fold and 1- to 16-fold higher than concurrent serum concentrations, respectively. No adverse reactions were detected after repeated IG administration.

Conclusions and Clinical Relevance—On the basis of pharmacokinetic values, minimum inhibitory concentrations of Rhodococcus equi isolates, and drug concentrations in PELF and bronchoalveolar cells, a single daily oral dose of 10 mg/kg may be appropriate for treatment of R equi infections in foals. Persistence of high azithromycin concentrations in PELF and bronchoalveolar cells 48 hours after discontinuation of administration suggests that after 5 daily doses, oral administration at 48-hour intervals may be adequate. (Am J Vet Res 2001;62:1870–1875)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine the effects of dexamethasone on development of IgG subclass responses following vaccination of healthy horses.

Animals—11 mature Thoroughbreds.

Procedure—Horses received 2 IM injections at 2- week intervals of a vaccine containing inactivated infectious bovine rhinotracheitis, bovine viral diarrhea, and parainfluenza-3 viral antigens and were then randomly assigned to 2 groups. Six horses received dexamethasone (0.2 mg/kg of body weight, IM) twice weekly for 8 weeks starting the day of the first vaccination. Five control horses received an equivalent volume of saline (0.9% NaCl) solution. Antigen-specific serum IgG subclass titers were determined weekly after vaccination by use of an ELISA.

Results—Vaccination resulted in similar antigen-specific serum IgG(T) titers in dexamethasone-treated and control horses. In contrast, although control horses developed IgGa and IgGb responses after vaccination, corticosteroid administration completely inhibited these responses in treated horses.

Conclusions and Clinical Relevance—Cortico steroids can have profound effects on primary immune responses in horses and can significantly affect IgG responses to inactivated vaccines. Corticosteroid treatment regimens commonly used to treat diseases in horses may result induction of a nonprotective IgG subclass response, leaving treated horses susceptible to disease. Additionally, mechanisms regulating IgGa and IgGb responses appear to differ from those regulating IgG(T) responses. Further defining these mechanisms is a critical step in designing effective vaccines, and corticosteroid-induced immunomodulation may be a valuable tool for studying immune responses in horses. (Am J Vet Res 2000;61:1530–1533)

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in American Journal of Veterinary Research

Abstract

Objective—To determine signalment, clinical findings, results of diagnostic testing, outcome, and postmortem findings in horses with West Nile virus (WNV) encephalomyelitis.

Design—Retrospective study.

Animals—46 horses with WNV encephalomyelitis.

Procedure—Clinical data were extracted from medical records of affected horses.

Results—On the basis of clinical signs and results of serologic testing, WNV encephalomyelitis was diagnosed in 46 of 56 horses with CNS signs. Significantly more males than females were affected. Increased rectal temperature, weakness or ataxia, and muscle fasciculations were the most common clinical signs. Paresis was more common than ataxia, although both could be asymmetrical and multifocal. Supportive treatment included anti-inflammatory medications, fluids, antimicrobials, and slinging of recumbent horses. Results of the IgM capture ELISA and the plaque reduction neutralization test provided a diagnosis in 43 horses, and only results of the plaque reduction neutralization test were positive in 3 horses. Mortality rate was 30%, and 71% of recumbent horses were euthanatized. One horse that had received 2 vaccinations for WNV developed the disease and was euthanatized. Follow-up communications with 19 owners revealed that most horses had residual deficits at 1 month after release from the hospital; abnormalities were resolved in all but 2 horses by 12 months after release.

Conclusions and Clinical Relevance—Our findings were similar to those of previous WNV outbreaks in horses but provided additional clinical details from monitored hospitalized horses. Diagnostic testing is essential to diagnosis, treatment is supportive, and recovery rate of discharged ambulatory horses is < 100%. (J Am Vet Med Assoc 2003;222:1241–1247)

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in Journal of the American Veterinary Medical Association