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To characterize antimicrobial prescribing patterns of clinicians and clinical services at a large animal veterinary teaching hospital and identify factors associated with antimicrobial prescribing.


All large animals (ie, equids, bovids, sheep, goats, camelids, swine, and cervids) evaluated at the New Bolton Center hospital at the University of Pennsylvania from 2013 through 2018.


In a cross-sectional study design, data on antimicrobial use by clinicians and clinical services were collected from administrative and billing records. Multivariable regression modeling was performed to identify factors associated with antimicrobial prescribing patterns.


Antimicrobials and critically important antimicrobials of the highest priority were dispensed in 42.1% (9,853/23,428) and 24.0% (2,360/9,853) of visits, respectively, and these proportions differed significantly among clinicians. Per visit, the median (interquartile [25th to 75th percentile] range) number of animal-defined daily doses dispensed was 3.6 (0.8 to 11.1) and the mean (SD) number of antimicrobial classes dispensed was 2.0 (1.3). Patient species, age, affected body system, and duration of hospitalization as well as submission of specimens for bacterial culture were significantly associated with prescribing patterns.


The frequency and quantity of antimicrobials prescribed differed significantly among clinicians within and across services, even for animals with clinical signs affecting the same body system. Patient- and visit-level factors explained some but not all of the heterogeneity in prescribing patterns, suggesting that other clinician-specific factors drove such practices. More research is needed to better understand antimicrobial prescribing patterns of clinicians, particularly in situations for which no antimicrobial use guidelines have been established.

Full access
in American Journal of Veterinary Research


Objective—To determine whether prolonged administration of clenbuterol results in tachyphylaxis, specifically regarding its bronchoprotective properties and effect on sweating in horses.

Animals—8 Thoroughbreds with inflammatory airway disease.

Procedures—In a crossover design, horses received clenbuterol (0.8 μg/kg, PO, q 12 h) or placebo for 21 days, with a washout period of ≥ 30 days between the 2 treatments. Airway reactivity was evaluated by use of flowmetric plethysmography and histamine broncho-provocation before (day 0; baseline) and every 7 days after the start of treatment. Sweat function was evaluated via response to epinephrine administered ID before and every 10 days after the start of treatment.

Results—The concentration of histamine required to increase total airway obstruction by 35% (PC35) was significantly reduced during treatment with clenbuterol (mean change, 11.5 mg/mL), compared with during administration of the placebo (mean change, −1.56 mg/mL), with a peak effect at 14 days. Tachyphylaxis was evident by day 21, with 7 of 8 horses having a PC35 below the baseline value (mean change, −0.48 mg/mL), which returned to baseline values during the washout period. No effect of clenbuterol was seen in sweat response to epinephrine administration.

Conclusions and Clinical Relevance—Clenbuterol initially reduced airway sensitivity to inhaled histamine, but tachyphylaxis that resulted in increased airway reactivity was evident by day 21. Although no effects on sweating were detected, the technique may not have been sensitive enough to identify subtle changes. Prolonged administration of clenbuterol likely results in a clinically important reduction in its bronchodilatory effects.

Full access
in American Journal of Veterinary Research


OBJECTIVE To determine the anabolic and lipolytic effects of a low dosage of clenbuterol administered orally in working and nonworking equids.

ANIMALS 8 nonworking horses and 47 polo ponies in active training.

PROCEDURES Each polo pony continued training and received either clenbuterol (0.8 μg/kg) or an equal volume of corn syrup (placebo) orally twice daily for 21 days, and then was evaluated for another 21-day period. Nonworking horses received clenbuterol or placebo at the same dosage for 21 days in a crossover trial (2 treatments/horse). For working and nonworking horses, percentage body fat (PBF) was estimated before treatment and then 2 and 3 times/wk, respectively. Body weight was measured at intervals.

RESULTS Full data sets were not available for 8 working horses. For working horses, a significant treatment effect of clenbuterol was detected by day 3 and continued through the last day of treatment; at day 21, the mean change in PBF from baseline following clenbuterol or placebo treatment was −0.80% (representing a 12% decrease in PBF) and −0.32%, respectively. By day 32 through 42 (without treatment), PBF change did not differ between groups. When treated with clenbuterol, the nonworking horses had a similar mean change in PBF from baseline from day 6 onward, which peaked at −0.75% on day 18 (an 8% decrease in PBF). Time and treatment had no significant effect on body weight in either experiment.

CONCLUSIONS AND CLINICAL RELEVANCE Among the study equids, long-term low-dose clenbuterol administration resulted in significant decreases in body fat with no loss in body weight.

Full access
in American Journal of Veterinary Research


Objective—To determine whether there are important differences relating to seasonality of signs or clinical features between subtypes of inflammatory airway disease (IAD) in horses caused by neutrophilic and eosinophilic-mastocytic inflammation having dissimilar etiopathologic pathways.

Design—Retrospective case series.

Animals—98 horses.

Procedures—Data were compiled from medical records of horses examined because of poor performance from 2004 through 2010. Horses underwent a standardized high-speed treadmill test, lameness evaluation, cardiac evaluation, and postexercise bronchoalveolar lavage (BAL). By means of standard BAL cytologic criteria, horses were divided into 4 groups: eosinophilic-mastocytic inflammation, neutrophilia only, mixed inflammation, or no inflammation (control). Associations between IAD subtype and clinical parameters were investigated.

Results—Data for 98 horses were obtained, including age, career, season of admission, and results of hematologic evaluation, high-speed treadmill arterial blood gas analysis, upper airway endoscopy, cardiologic evaluation, and BAL. Cytologic evidence of IAD was found in 81% (79/98) of the horses, and 30% (30/98) had erythrocytes present in the BAL fluid after exercise. Horses in the eosinophilic-mastocytic inflammation and mixed-inflammation groups were significantly more likely to be Thoroughbred than Standardbred and have larger amounts of mucus in their BAL fluid. No significant differences were found in season of evaluation, results of exercising blood gas analyses, or comorbidities.

Conclusions and Clinical Relevance—No association between season and cytologic profile of BAL fluid and no major effects of IAD subtype on pulmonary gas exchange during exercise were seen in this population of horses.

Full access
in Journal of the American Veterinary Medical Association


Case Description—5 horses were evaluated because of decreased appetite, weight loss, fever, cough, tachypnea, and respiratory distress.

Clinical Findings—Tachycardia, tachypnea, increased respiratory effort, lethargy, fever, poor body condition, and nasal discharge were detected in various combinations on initial physical examination. Evaluation of the lower portion of the respiratory tract via radiography and ultrasonography revealed a severe nodular interstitial pattern. Histologic examination of lung tissue revealed interstitial expansion of alveolar parenchyma with collagen, intraluminal accumulation of neutrophils and macrophages within the alveoli, and occasional intranuclear inclusion bodies within alveolar macrophages. Equine herpesvirus type 5 was detected in samples of lung tissue, bronchoalveolar lavage fluid, or both via polymerase chain reaction assay in all cases. A diagnosis of equine multinodular pulmonary fibrosis (EMPF) was established.

Treatment and Outcome—Horses were provided supportive treatment and were administered a variety of medications including corticosteroids and acyclovir. Two horses survived and returned to their previous level of activity. Three horses were euthanized because of either deterioration of clinical condition (n = 2) or failure to improve within 4 weeks of initiation of treatment (1).

Clinical Relevance—EMPF should be considered as a differential diagnosis for adult horses with interstitial pneumonia and should be suspected on the basis of characteristic radiographic, ultrasonographic, and histopathologic findings. Equine herpesvirus type 5 is found in association with EMPF; although the exact pathogenic role this virus plays in EMPF is unknown, equine herpesvirus type 5 may be an etiologic agent or cofactor in the development of EMPF.

Full access
in Journal of the American Veterinary Medical Association