Mild-moderate equine asthma: A scoping review of evidence supporting the consensus definition

Current consensus defines mild-moderate equine asthma (mEA; previously inflammatory airway disease) by a hierarchy of indicators of lung pathology: cough, poor performance, increased tracheobronchial mucus, inflammatory bronchoalveolar lavage (BAL) cytology and pulmonary dysfunction. Exclusion criteria include fever, systemic disease, or increased resting respiratory effort. The aim of this review was to inform future research by identifying gaps, strengths and weaknesses in the current body of evidence supporting this consensus-proposed definition. Objectives were to critique evidence supporting the inclusion of each diagnostic indicator in the case definition, by summarising and evaluating evidence for its association with higher-level indicators of lung inflammation. Searches of three databases identified 2275 articles relating to mEA or its diagnostic indicators, from which 298 full-text articles were screened and 45 reviewed in full. Studies (n = 44) had been performed worldwide in clinics, hospitals, racetracks, yards or research herds, in 6092 horses. Studies were predominantly opportunistic observational (n = 13/44: 29.5%) or cross-sectional (n = 11/44; 25%). The median number of horses per study was 74. Where breed and use were reported most were Thoroughbreds (58.2%; 2730/4688) and racehorses (72.8%; n = 3960/5439). Domains rated as high risk of bias in almost 50% of articles were 'study power' and 'masking'. Heterogeneity in clinical and laboratory measures precluded meta-analysis. Evidence was more consistent for certain pairwise relationships (e.g., between cough and tracheobronchial mucus) than others (e.g., BAL cytology and lung function). Findings highlight the need for increased standardisation of diagnostic methods and reporting to facilitate future systematic review and meta-analysis.

Effects of forages, dust exposure and proresolving lipids on airway inflammation in horses

OBJECTIVE

To investigate the role of omega-3 polyunsaturated fatty acids (Ω-3)-derived proresolving lipid mediators (PRLM) in the resolution of mild airway inflammation in horses.

ANIMALS

20 horses with mild airway inflammation.

PROCEDURES

Horses previously eating hay were fed hay pellets (low Ω-3 content; n = 10) or haylage (high Ω-3 content; 9) for 6 weeks. Dust exposure was measured in the breathing zone with a real-time particulate monitor. Bronchoalveolar lavage (BAL) was performed at baseline, week 3, and week 6. The effect of PRLM on neutrophil apoptosis and efferocytosis was examined in vitro. BAL fluid inflammatory cell proportions, apoptosis of circulating neutrophils, efferocytosis displayed by alveolar macrophages, and plasma lipid concentrations were compared between groups fed low and high amounts of Ω-3 by use of repeated measures of generalized linear models.

RESULTS

Dust exposure was significantly higher with hay feeding, compared to haylage and pellets, and equivalent between haylage and pellets. BAL fluid neutrophil proportions decreased significantly in horses fed haylage (baseline, 11.8 ± 2.4%; week 6, 2.5 ± 1.1%) but not pellets (baseline, 12.1 ± 2.3%; week 6, 8.5% ± 1.7%). At week 6, horses eating haylage had significantly lower BAL neutrophil proportions than those eating pellets, and a significantly lower concentration of stearic acid than at baseline. PRLM treatments did not affect neutrophil apoptosis or efferocytosis.

CLINICAL RELEVANCE

Despite similar reduction in dust exposure, horses fed haylage displayed greater resolution of airway inflammation than those fed pellets. This improvement was not associated with increased plasma Ω-3 concentrations. Feeding haylage improves airway inflammation beyond that due to reduced dust exposure, though the mechanism remains unclear.

Evaluation of the airway mechanics of modified toggle laryngoplasty constructs using a vacuum chamber airflow model

OBJECTIVE

To evaluate the airway mechanics of modified toggle LP constructs in an airflow chamber model and compare these to the airway mechanics of standard LP constructs.

STUDY DESIGN

Ex-vivo experimental study.

SAMPLE POPULATION

Fifty-one equine cadaveric larynges.

METHODS

Bilateral LP constructs were performed using a modified toggle (n = 23) or a standard (n = 21) LP technique. Constructs were tested in an airflow model before and after cyclic loading which was designed to mimic postoperative swallowing. The cross-sectional area (CSA), peak translaryngeal airflow (L/s), and impedance (cmH₂ 0/L/s) were determined and compared between LP constructs before and after cycling.

RESULTS

The mean CSA of the rima glottidis of the modified toggle LP constructs was 15.2 ± 2.6 cm² before and 14.7 ± 2.6 cm² after cyclic loading, and the mean CSA of the rima glottidis of the standard LP constructs was 16.4 ± 2.9 cm² before and 15.7 ± 2.8 cm² after cyclic loading. The modified toggle LP constructs had similar peak translaryngeal impedance before and after cyclic loading (p = .13); however, the standard LP constructs had higher peak translaryngeal impedance after cyclic loading (p = .02).

CONCLUSION

The modified toggle and standard LP constructs had comparable airway mechanics in an ex-vivo model.

CLINICAL SIGNIFICANCE

Further investigation is warranted to determine the extent to which the modified toggle LP technique restores normal airway function in horses with RLN.

An observational study of environmental exposures, airway cytology, and performance in racing thoroughbreds

Background

Mild equine asthma is presumed to arise in response to environmental exposures but the relative impact of differing inflammatory phenotypes upon performance are largely unexplored.

Hypotheses: Airway inflammation negatively affects performance and cytological phenotype varies with environmental exposure.

Animals

Thoroughbred racehorses in active training and racing.

Methods

Thoroughbreds were recruited 24‐48 hours before racing. Each horse was eligible for re‐enrollment with each race entry. Within one hour of race completion, physical examination, respiratory endoscopy, and BAL were performed. Respirable and inhalable dust, respirable endotoxin, and respirable β‐glucan exposures were measured at the breathing zone within one week after racing. Controlling for age, trainer, and pulmonary hemorrhage, the relationship between performance, bronchoalveolar lavage fluid (BALF) cytology, and measures of exposure were modeled.

Results

Performance and BALF data were collected on 64 individual horses from 8 stables for a total of 98 race performances and 79 dust exposure assessments. Evidence of mild equine asthma was found in 80% (78/98) of BALF samples from 52/64 horses. For each percent increase in BALF mast cell and neutrophil proportions, speed figures were reduced by 2.9 (P = .012) and 1.4 (P = .046) points, respectively. Respirable dust concentration was associated with BALF neutrophil proportions (P = .015). Bronchoalveolar lavage fluid mast cell proportions were only associated with respirable β‐glucan exposures (P = .030).

Conclusions and Clinical Importance: Mild equine asthma is common in racing horses and negatively impacts performance. The data support that respirable, rather than inhalable, dust exposure measures are pertinent to equine airway health.

Hypertrichosis in a Horse with Alimentary T-Cell Lymphoma and Pituitary Involvement

A 13-year-old Quarterhorse mare had a 6-month history of diarrhea, progressive weight loss, and lethargy. At presentation the mare was hirsute, had hyperhidrosis, and abnormal fat distribution in addition to severe diarrhea. A presumptive clinical diagnosis of protein-losing enteropathy and pituitary pars intermedia dysfunction was made. T-cell lymphoma was diagnosed in a rectal biopsy specimen. The owner elected to euthanize the mare because of poor prognosis and the severity of the disease. At necropsy, the mare had hypertrichosis and the pituitary gland was diffusely enlarged. Histologically, neoplastic lymphocytes infiltrated the gastrointestinal mucosa, mesenteric lymph nodes, and the pituitary gland. In addition, there was hyperplasia of the pituitary gland pars intermedia. Pituitary adenoma was not present. Hypertrichosis in this case could have been triggered by a combination of adenomatous hyperplasia of pars intermedia and lymphoma resulting in disruption of the hypothalamic dopaminergic tone or disruption of the hypothalamic thermoregulatory center.

Evaluation of a PCR to Detect Salmonella in Fecal Samples of Horses Admitted to a Veterinary Teaching Hospital

The diagnostic accuracy of a PCR used to identify horses shedding Salmonella spp. in their feces during hospitalization was estimated, relative to bacterial culture of serially collected fecal samples, using longitudinal data. Five or more fecal samples were collected from each of 116 horses admitted as inpatients, for reasons other than gastrointestinal disease, between July 26, 2001 and October 25, 2002. All 873 fecal samples collected were tested with a PCR based on oligonucleotide primers defining a highly conserved segment of the histidine transport operon gene of Salmonella typhimurium, and each sample was cultured for Salmonella spp. One or more samples from 87 (75%) horses were PCR positive, and Salmonella was cultured from 1 or more samples from 11 (9.5%) horses. All culture-positive horses had at least 1 PCR-positive result, whereas only 29 (28%) culture-negative horses were PCR negative on all fecal samples tested. The PCR was most specific, relative to bacterial culture of serially collected fecal samples, when used to test samples from Quarterhorse or breeds other than Thoroughbred or Standardbred, or from clinical (vs. healthy, accompanying horses) cases. Overall, the PCR had the greatest agreement (70%), compared with bacterial culture of serially collected fecal samples, using a cutoff of 2 or more positive PCR test results to define a Salmonella-positive horse. The reasons why some fecal samples, from which Salmonella organisms cannot be isolated, are PCR positive need to be determined before the PCR can be incorporated into Salmonella surveillance programs for hospitalized equine populations.

Efficacy of Inhaled Levalbuterol Compared to Albuterol in Horses with Recurrent Airway Obstruction

Background

The (R)‐enantiomer of racemic albuterol (levalbuterol) has bronchodilatory properties whereas the (S)‐enantiomer causes adverse effects in human airways, animal models, and isolated equine bronchi. Levalbuterol is commercially available and improves pulmonary function of asthmatic patients with a longer duration of effect than albuterol.

Objective

To determine the dose at which inhaled levalbuterol produces maximal bronchodilatory effect (EDmax) and determine its duration of action in recurrent airway obstruction (RAO)‐affected horses in comparison to racemic albuterol.

Animals

Nine horses with inducible and reversible RAO.

Methods

Randomized, crossover trial. Horses were challenged with moldy hay to induce airway obstruction. Horses were treated with nebulized albuterol or levalbuterol chosen randomly. Pulmonary function testing (PFT) was measured before and for up to 3 hours after bronchodilatation challenge. Maximum change in transpulmonary pressure (DP_max) was measured to assess the dose effect and duration of action of each drug. After a 24 hours washout period, the bronchodilatation challenge was repeated with the second bronchodilator.

Results

The duration of effect was 60 minutes for albuterol and 120 minutes for levalbuterol. The dose of bronchodilator EDmax was not significantly different between albuterol and levalbuterol (EDmax = 125.0 [125–125 μg] and EDmax = 188 [125–188 μg] respectively; P = .068). The magnitude of bronchodilatation was not significantly different between the 2 treatments (61.1 and 59.9% decrease in DP_max for albuterol and levalbuterol respectively; P = .86).

Conclusions and clinical importance

Levalbuterol is as effective a bronchodilator as albuterol; although levalbuterol lasts twice as long as albuterol, its duration of action is still too short to make it practical for RAO treatment.

Inflammatory Airway Disease of Horses--Revised Consensus Statement

The purpose of this manuscript is to revise and update the previous consensus statement on inflammatory airway disease (IAD) in horses. Since 2007, a large number of scientific articles have been published on the topic and these new findings have led to a significant evolution of our understanding of IAD.

Investigating the link between particulate exposure and airway inflammation in the horse

Inhalant exposure to airborne irritants commonly encountered in horse stables is implicated in the pathogenesis of inflammatory airway disease (IAD) and recurrent airway obstruction (RAO), non‐infectious, inflammatory pulmonary disorders that impact the health and performance of horses across all equine disciplines. IAD and RAO have overlapping clinical, cytological, and functional manifestations of the pulmonary response to organic dust and noxious gases encountered in the barn environment. Study of these diseases has provided important but incomplete understanding of the effect of air quality upon the respiratory health of horses. In this review, the principles of particulate exposure assessment, including health‐related aerosol size fractions and size‐selective sampling, the factors influencing air quality in equine environments, and the effect of air quality on the equine respiratory tract are discussed. The objective of this review is to provide the reader with a summary of the most common chronic inflammatory airway diseases in the horse and the principles of air sampling that are essential to the planning, interpretation, and assessment of equine respiratory health‐related exposure studies.

Environmental exposures and airway inflammation in young thoroughbred horses

Background

Inflammatory airway disease (IAD) in horses is a widespread, performance‐limiting syndrome believed to develop in response to inhaled irritants in the barn environment.

Objectives

To evaluate changes in bronchoalveolar lavage fluid (BALF) cytology and exposure to particulates, endotoxin, and ammonia during horses' first month in training.

Animals

Forty‐nine client‐owned 12‐ to 36‐month‐old Thoroughbred horses entering race training.

Methods

In this prospective cohort study, a convenience sample of horses was assigned to be fed hay from a net (n = 16), whereas the remaining horses were fed hay from the ground (n = 33). BALF was collected at enrollment and after 14 and 28 days in training. Respirable particulate, inhalable particulate, respirable endotoxin, and ammonia concentrations were measured at the breathing zone of each horse weekly.

Results

Median respirable particulates were significantly higher when horses were fed from hay nets than when fed hay from the ground (hay net 0.28 mg/m³, no hay net 0.055 mg/m³, P < .001). Likewise, inhalable particulate (hay net 8.3 mg/m³, no hay net 3.3 mg/m³, P = .0064) and respirable endotoxin (hay net 173.4 EU/m³, no hay net 59.2 EU/m³, P = .018) exposures were significantly higher when horses were fed from hay nets. Feeding hay from a net resulted in significantly higher BALF eosinophil proportions over time (P < .001). BALF eosinophils were significantly related to respirable particulate exposure (14 days in training r_s = 0.37, P = .012, 28 days in training, r_s = 0.38, P = .017).

Conclusions and Clinical Importance

Pulmonary eosinophilic inflammation develops in response to respirable particulate exposure in young Thoroughbreds, indicating a potential hypersensitivity to inhaled particulate allergens.

Comparison of two analyzers for measurement of plasma total carbon dioxide concentration in horses

OBJECTIVE

To determine the degree of agreement between 2 analyzers for measurement of total CO₂ concentration (ctCO₂) in equine plasma.

ANIMALS

6 healthy untrained horses, 6 trained Standardbreds undergoing a simulated race protocol, and 135 trained Standardbreds at a racetrack.

PROCEDURES

Jugular venous blood samples were obtained from all horses. Two analyzers (commonly used analyzer A and less expensive analyzer B) were used to measure plasma ctCO₂ in each sample. Validation of both analyzers was conducted in accordance with guidelines established by the Clinical and Laboratory Standards Institute and involved characterization of linearity, total analytic error, and bias estimation.

RESULTS

Total analytic error (instrument SD) was 0.58 mmol/L (coefficient of variation, 1.6%) and 0.49 mmol/L (coefficient of variation, 1.4%) for analyzers A and B, respectively, when measuring an aqueous standard containing 36.0 mmol of CO₂/L. A 1 g/L decrease in plasma protein concentration corresponded to an increase in ctCO₂ measured with analyzer B of 0.065 mmol/L. A difference plot indicated that analyzer B produced values 2.7% higher than analyzer A for 103 samples from the 6 trained and exercised Standardbreds (mean plasma protein concentration, 67 g/L).

CONCLUSIONS AND CLINICAL RELEVANCE

Analyzer B provided adequate precision and linearity for measurement of ctCO₂ from 5 to 40 mmol/L and was therefore suitable for measuring ctCO₂ in equine plasma, provided allowances are made for changes in plasma protein concentration.

Effect of sample handling and storage time on the stability of total CO2 in equine plasma

REASONS FOR PERFORMING STUDY

The stability of total CO2 concentration (ctCO2) in plasma is influenced by storage temperature and handling during sample processing. Conflicting information exists regarding the stability of ctCO2 in equine plasma over time, and the effect of centrifugation on the measured value for plasma ctCO2 is unclear.

OBJECTIVES

To determine plasma ctCO2 stability over 5 days when equine blood is collected into Vacutainer tubes, centrifuged within 30 min of collection, and stored at 4 degrees C; and to determine whether a delay in centrifugation increases the rate at which plasma ctCO2 decreases over time.

METHODS

Blood was collected from 6 adult horses into 3 ml plastic Vacutainer tubes and randomly assigned to be centrifuged immediately, or after, storage. Plasma ctCO2 was measured in triplicate at 0, 24, 48, 72 and 96 h after collection using a NOVA-4 analyser Data were analysed using multivariable linear regression, with P < 0.05 being defined as significant.

RESULTS

Plasma ctCO2 decreased linearly over time during storage at 4 degrees C. The measured value for ctCO2 decreased at a faster rate (-0.28 mmol/l/day; P < 0.0001) when centrifugation was delayed, compared with immediate centrifugation (-0.10 mmol/l/day). There was a significant effect of sequence of sample analysis on the ctCO2 value when measured in triplicate: the second and third measurements were 0.31 and 0.41 mmol/l lower than the first measurement, respectively.

CONCLUSIONS

Blood samples collected from horses into Vacutainer tubes should be centrifuged immediately after collection and analysed as soon as possible to ensure accurate values for plasma ctCO2.

POTENTIAL RELEVANCE

Failure to centrifuge, or excessive delay in measuring ctCO2 after centrifugation, produces values significantly lower than the true value.

Effect of the size of evacuated blood collection tubes on total carbon dioxide concentration in equine plasma

OBJECTIVE

To determine whether plasma total CO(2) concentrations would vary with the size of the evacuated tube used to collect blood samples.

DESIGN

Randomized crossover study.

ANIMALS

Convenience sample of 20 healthy adult horses.

PROCEDURES

Jugular venous blood was collected from horses in random order into 8 types of evacuated tubes: 2-mL glass, 2- or 3-mL plastic or plastic plasma separator, 4- or 6-mL plastic, and 10-mL glass or plastic. Total CO(2) concentrations in plasma were measured with a biochemistry analyzer. Data were analyzed via repeated-measures ANOVA and multivariate regression.

RESULTS

The air volume-to-blood volume ratio was significantly higher and consequently, plasma total CO(2) concentration was significantly lower when blood was collected into 2-mL glass tubes and 2- or 3-mL plastic tubes than when the other 5 types of evacuated tubes were used. Concentrations in the other tube types were statistically equivalent. A linear relationship was detected between total CO(2) concentration and air volume-to-blood volume ratio.

CONCLUSIONS AND CLINICAL RELEVANCE

Blood samples should be collected into evacuated tubes with a small air volume-to-blood volume ratio whenever an accurate estimate of plasma total CO(2) concentration is required.

Comparative efficacy of inhaled albuterol between two hand-held delivery devices in horses with recurrent airway obstruction

REASONS FOR PERFORMING STUDY

Studies investigating the clinical efficacy of albuterol administered with the same propellant and commercially available delivery devices in horses with recurrent airway obstruction (RAO) are not currently available.

OBJECTIVES

To determine the efficacy of aerosolised albuterol administered to horses with RAO by means of 2 commercially available, hand-held delivery devices.

METHODS

Ten horses with RAO were kept in a dusty environment and fed mouldy hay to induce airway obstruction. Lung mechanics were measured before and after the procedure. ΔP(max) was measured 5 min after administration of 180 µg of albuterol from a pressurised metered dose inhaler, using an aerosol delivery device chosen randomly. This process was repeated every 5 min until maximal bronchodilation was achieved. After a 24 h washout period, lung mechanics data were again collected using the other aerosol delivery device.

RESULTS

Aerosolised albuterol induced a significant and rapid bronchodilation in the horses using both aerosol delivery devices. No statistically significant difference in pulmonary function was observed in response to albuterol therapy between the 2 devices. The dose required to achieve 50% of maximal bronchodilation was not statistically different between the 2 devices (173.35 ± 78.35 µg with Device 1 and 228.49 ± 144.99 µg with Device 2, P = 0.26). The decrease in lung resistance tended to be more pronounced after albuterol administration with Device 1 (P = 0.066).

CONCLUSIONS

Aerosolised albuterol is an effective bronchodilator in horses with recurrent airway obstruction. There is no statistically significant difference between the 2 commercially available aerosol delivery devices in terms of efficacy.

POTENTIAL RELEVANCE

Aerosolised albuterol is effectively delivered using currently available devices leading to maximal bronchodilation in horses with RAO at an average dose of 540 µg.

Effect of furosemide and furosemide-carbazochrome combination on exercise-induced pulmonary hemorrhage in Standardbred racehorses

The objective was to quantify the effect of furosemide and carbazochrome on exercise-induced pulmonary hemorrhage (EIPH) in Standardbred horses using red blood cell count and hemoglobin concentration in bronchoalveolar lavage (BAL) fluid. Six healthy Standardbred horses with prior evidence of EIPH performed a standardized treadmill test 4 h after administration of placebo, furosemide, or furosemide-carbazochrome combination. Red blood cell (RBC) counts and hemoglobin concentrations were determined on the BAL fluid. The RBC count in BAL ranges were (2903-26,025 cells/microL), (45-24,060 cells/microL), and (905-3045 cells/microL) for placebo, furosemide, and furosemide-carbazochrome, respectively. Hemoglobin concentration ranges were (0.03-0.59 mg/mL), (0.01-0.55 mg/mL), and (0.007-0.16 mg/mL) for placebo, furosemide, and furosemide-carbazochrome groups, respectively. No significant differences were detected among treatments. However, there was great variability among horses, suggesting that a larger sample size or better selection of horses was needed.

Lung function and airway cytologic profiles in horses with recurrent airway obstruction maintained in low-dust environments

BACKGROUND

The effects of long-term environmental management on airway obstruction and inflammation in horses with recurrent airway obstruction (RAO) are unknown.

HYPOTHESIS

Horses with RAO maintained in low-dust environments have persistent airway obstruction and neutrophilic inflammation.

ANIMALS

Study horses were treated for RAO and then maintained in low-dust environments with no medical management. Horses were classified into 3 groups by years after diagnosis: 1 year (time 1, n = 9), 2-3 years (time 2, n = 7), and 5-6 years (time 3, n = 8). The comparison groups were age-matched healthy horses.

METHODS

In this cross-sectional study, a clinical examination was performed, and the clinical score was calculated. Standard lung function, forced expiratory maneuvers, and the cytology of bronchoalveolar lavage fluid (BALF) were evaluated.

RESULTS

The clinical scores of the RAO horses were higher than those of the non-RAO horses at time 2 (P = .018). Standard lung function data were not different between the groups at any time point. The forced expiratory flow between 75-95% of exhaled vital capacity was lower in RAO horses than in non-RAO horses at all time points (P < .02), indicating persistent peripheral airway obstruction. Cytologic evaluation of BALF revealed no difference in total nucleated cell numbers or differential cell counts between RAO and non-RAO horses at any time point.

CONCLUSIONS AND CLINICAL IMPORTANCE

The peripheral airway obstruction detected in horses with RAO maintained in low-dust environments likely is due to irreversible airway remodeling but is not associated with cytologic evidence of airway inflammation.

Inflammatory airway disease of horses

The purpose of this consensus statement is to provide a review of current knowledge and opinions concerning inflammatory airway disease (IAD) and to help practitioners differentiate IAD from heaves (or recurrent airway obstruction; RAO) and other inflammatory respiratory diseases of horses.

DNA binding activity of transcription factors in bronchial cells of horses with recurrent airway obstruction

Horses with recurrent airway obstruction (RAO) present many similarities with human asthmatics including airway inflammation, hyperresponsiveness, reversible obstruction, and increased NF-kappaB expression. Studies in experimental asthma models have shown that transcriptions factors such as activator protein-1 (AP-1), GATA-3, cyclic AMP response element binding protein (CREB) and CAAT/enhancer binding protein (C/EBP) may also play an important role in airway inflammation. The purpose of this study was to measure DNA binding activity of these transcription factors in the airways of horses with RAO and to compare it to pulmonary function and bronchoalveolar lavage fluid (BALF) cytology. Seven horses with RAO and six control animals were studied during a moldy hay challenge and after 2 months at pasture. Pulmonary function, BALF cytology and transcription factors' activities in bronchial brushings were measured during hay and pasture exposures. During moldy hay challenge, RAO-affected horses developed severe airway obstruction and inflammation and a significantly higher airway AP-1 binding activity than in controls. After 2 months on pasture, pulmonary function and airway AP-1 binding activity were not different between RAO and control horses. The DNA binding activity of CREB in airways of RAO-affected horses increased significantly after 2 months at pasture and became higher than in controls. A significant positive correlation was detected between AP-1 binding activity and indicators of airway obstruction and inflammation. Airway GATA-3, CEBP and CREB binding activities were negatively correlated with indices of airway obstruction. However, contrarily to CREB binding activity, GATA-3 and CEBP binding activities were not different between RAO and control horses and were unaffected by changes in environment. These data support the view that AP-1 and CREB play a role in modulating airway inflammation in horses with RAO.

Effect of beclomethasone dipropionate and dexamethasone isonicotinate on lung function, bronchoalveolar lavage fluid cytology, and transcription factor expression in airways of horses with recurrent airway obstruction

Glucocorticoid (GC) therapy is recognized to be effective for the treatment of recurrent airway obstruction (RAO) in horses. Anti-inflammatory properties of GC are thought to be mediated by suppression of inflammatory gene expression via inhibition of transcription factors such as nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1). The purpose of this study was to evaluate the effect of low-dose inhaled beclomethasone dipropionate and injectable dexamethasone 21-isonicotinate on clinical signs, pulmonary function, airway cytology, and activity of NF-kappaB and AP-1 in bronchial cells of RAO-affected horses. Seven horses with RAO were exposed to moldy hay until they developed airway obstruction on 3 separate occasions. In a crossover design, they were then treated with a placebo (injection on day 1), inhaled beclomethasone (500 microg q12h for 10 days), or dexamethasone (0.06 mg/kg, IM on day 1) and monitored for 10 days. Pulmonary function, bronchoalveolar lavage fluid cytology, and NF-kappaB and AP-1 activity in bronchial brushing cells were measured before (day 1) and after treatment (day 10). Treatment with beclomethasone resulted in significantly improved pulmonary function of RAO-affected horses compared with placebo and dexamethasone treatments. However, none of the treatments had an effect on bronchoalveolar lavage fluid cytology or NF-kappaB and AP-1 activity. These findings reveal that, in a model of severe RAO, the benefits of low-dose inhaled beclomethasone on pulmonary function are not accompanied by a decrease in airway inflammatory cells or a suppression of transcription factors NF-kappaB and AP-1 DNA-binding activity.

Randomized, controlled study of inhaled fluticasone propionate, oral administration of prednisone, and environmental management of horses with recurrent airway obstruction

OBJECTIVE

To determine whether administration of glucocorticoids provides additional benefits to environmental management of horses with recurrent airway obstruction (RAO).

ANIMALS

28 horses with RAO.

PROCEDURE

Horses were classified as having mild, moderate, or severe RAO. Within each category, horses were randomly assigned to receive inhaled fluticasone propionate, inhaled control substance, or oral administration of prednisone. During the 4-week study, horses were maintained outdoors and fed a pelleted feed. Clinical scores, pulmonary function, results of cytologic examination of bronchoalveolar lavage fluid (BALF), and adrenal gland function were determined before and 2 and 4 weeks after initiation of treatment.

RESULTS

Clinical score and pulmonary function of all RAO-affected horses improved during the treatment period. After 4 weeks, clinical scores and pulmonary function of horses treated with a glucocorticoid were not different from those for the control treatment. In horses with severe RAO, treatment with fluticasone for 2 weeks resulted in significantly greater improvement in pulmonary function, compared with pulmonary function after treatment with prednisone or the control substance. Treatment with a glucocorticoid for 4 weeks and a low-dust environment did not have any effect on cellular content of BALF Treatment with prednisone for 2 weeks resulted in a significant decrease in serum cortisol concentration, compared with concentrations after administration of fluticasone or the control substance.

CONCLUSIONS AND CLINICAL RELEVANCE

Environmental management is the most important factor in the treatment of horses with RAO. Early treatment with inhaled fluticasone can help accelerate recovery of horses with severe RAO.

Climatic and aeroallergen risk factors for chronic obstructive pulmonary disease in horses

OBJECTIVE

To estimate the association between climate and airborne pollen and fungal factors and chronic obstructive pulmonary disease (COPD) in horses.

SAMPLE POPULATION

Data from 1,444 horses with a diagnosis of COPD.

PROCEDURE

The Veterinary Medical Database was used to identify records of horses admitted to veterinary teaching hospitals in the United States and Canada between 1990 and 1999. Rainfall, mean minimum and maximum temperature, and maximum monthly pollen and fungal spore (mold) counts recorded at the city closest to where the hospital is located were identified for each month data were reported to the Veterinary Medical Database. Associations between climatic and aeroallergen data and monthly prevalence of COPD were estimated by use of cross-correlation and logistic regression models.

RESULTS

Significant positive correlations were found between prevalence of COPD and rainfall 3 months previously, minimum temperature 1 and 2 months previously, total pollen counts measured 3 months previously, and total mold counts measured during the same month and 1 month previously.

CONCLUSIONS AND CLINICAL RELEVANCE

Outdoor aeroallergens and climatic factors may contribute to the occurrence of COPD in horses.

Investigation and control of an outbreak of salmonellosis caused by multidrug-resistant Salmonella typhimurium in a population of hospitalized horses

An outbreak of salmonellosis in a population of hospitalized horses resulted in the closure of a teaching hospital for a period of 10 weeks. Fecal samples were collected from suspected cases and cultured for Salmonella. Salmonella isolates were characterized using antimicrobial susceptibility testing, pulsed-field gel electrophoresis (PFGE) and phage typing. Thirty-three cases of infection by a multidrug-resistant strain of S. typhimurium were detected. The index case was admitted on 26 August 1999. Fifteen (45%) cases occurred between April and June 2000. PFGE results suggested that this strain of S. typhimurium might have been introduced into the hospital environment by a foal presenting with diarrhea. The hospital was closed on June 13, and intensive environmental cleaning and disinfection were completed. Enforcement of infectious disease control protocols in hospitals and environmental and patient surveillance is needed to prevent outbreaks of salmonellosis.

Use of continuous-flow peritoneal dialysis for the treatment of acute renal failure in an adult horse

A 15-year-old Paso Fino gelding was evaluated because of acute renal failure following an episode of exertional rhabdomyolysis. The horse was azotemic and treated conservatively at another referral practice with no improvement in the azotemia. With conservative treatment and intermittent peritoneal dialysis, the horse had minimal improvement. Continuous-flow peritoneal dialysis (CFPD) was instituted on day 7 and continued for 3 consecutive days. Dramatic changes in the horse's attitude and serum creatinine concentration were detected within the first 24 hours of CFPD treatment. The horse remained hospitalized for 23 days; within 3 months of discharge, serum BUN and creatinine concentrations had returned to within the reference ranges and the horse had resumed normal activity. In adult horses, it appears that CFPD can be used to successfully treat acute renal failure that is refractory to conventional treatments.

Effect of airway disease on blood gas exchange in racehorses

Inflammatory Airway Disease (IAD), exercise-induced pulmonary hemorrhage (EIPH), and upper airway obstruction (UAO) are common respiratory tract diseases that can decrease performance. The purpose of this retrospective study was to compare bronchoalveolar lavage fluid cytology and arterial blood gas analysis during a treadmill test by poorly performing racehorses presented to Purdue University. One hundred thirty-two horses with a history of poor performance were included in this study. Ten horses with no history or diagnosis of EIPH, IAD, or UAO served as controls. Horses were evaluated by rhinolaryngoscopy for upper airway abnormalities and underwent a standardized treadmill test, and samples were collected for blood gas analysis. Horses with IAD or EIPH had a more severe exercise-induced hypoxemia, (mean+/-SD; 84.8+/-1.5 and 86.0+/-1.7 mm Hg average Pao2, respectively), than horses in the control group (92.8+/-2.1 mm Hg). The average Pao2 of horses with only UAO (88.3+/-3.3 mm Hg) was not significantly different from control horses. Gas exchanges were the most severely impaired in horses affected with both EIPH and UAO because they exhibited the lowest Pao2 and highest Paco2 values (66.5+/-15.2 and 52.2+/-6.3 mm Hg, respectively).

Treatment of tracheal collapse with an intraluminal stent in a Miniature Horse

A 7-month-old miniature horse was referred for respiratory distress. Tracheal collapse at the level of the thoracic inlet was diagnosed. An intraluminal nitinol stent was placed with endoscopic guidance. Respiratory function was restored immediately after stent placement. The main complication observed during a 14-month follow-up period was growth of granulation tissue through the stent, which was controlled satisfactorily by electrocautery performed during endoscopy with the horse standing. Treatment of tracheal collapse with an intraluminal stent is an effective, practical, and minimally invasive procedure in miniature and young equids and ponies.

Detection of Salmonella organisms and assessment of a protocol for removal of contamination in horse stalls at a veterinary teaching hospital

OBJECTIVES

To assess methods of detecting environmental contamination with Salmonella organisms and evaluate a cleaning and disinfection protocol for horse stalls in a veterinary teaching hospital.

DESIGN

Original study.

SAMPLE POPULATION

37 horses with diarrhea likely to be caused by Salmonella infection and their stall environments.

PROCEDURES

Fecal samples were collected from horses daily during hospitalization; samples were obtained from stall sites after cleaning and application of disinfectants. Fecal and environmental samples were cultured for Salmonella spp and tested via polymerase chain reaction (PCR) assay to detect Salmonella DNA.

RESULTS

1 horse died and 2 were discharged prior to sample collection. Fecal samples from 9 of 34 horses yielded growth of Salmonella organisms on bacteriologic culture, and 23 yielded positive results via PCR assay on > or = 1 occasion. Among environmental samples from 21 stalls, salmonellae were detected at > or = 1 stall site on 6 of 78 occasions, and > or = 1 stall site yielded positive results via PCR assay on 69 of 77 occasions. Salmonella DNA was detected more frequently in samples of stall drains, cracks, and corners. Salmonella spp were cultured from samples of 3 stalls after both initial and second cleaning and disinfection cycles, but no organisms were detected in samples obtained after use of a peroxygen disinfectant.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that stalls in which horses with salmonellosis were housed should only be used to accommodate newly hospitalized horses after samples (collected after 2 cycles of cleaning and disinfection) from drains, cracks, and corners yield negative results on bacteriologic culture.

Analysis of risk factors for recurrent airway obstruction in North American horses: 1,444 cases (1990-1999)

OBJECTIVE

To identify risk factors for recurrent airway obstruction (RAO) among horses examined at veterinary teaching hospitals in North America.

DESIGN

Retrospective case-control study.

ANIMALS

1,444 horses with RAO and 1,444 control horses examined for other reasons.

PROCEDURE

The Veterinary Medical Database was searched for records of horses in which RAO was diagnosed. A control group was identified by randomly selecting a horse with a diagnosis other than RAO that matched the institution and year of admission for each of the horses with RAO. Information obtained included hospital, admission year and month, age, sex, breed, and discharge status. The association between risk factors and diagnosis of RAO was estimated with logistic regression models.

RESULTS

The risk of RAO increased significantly with age, with horses > or = 7 years old being 6 to 7 times as likely to have RAO as were horses < or = 4 years old. Thoroughbreds were 3 times as likely to have RAO as were ponies. Horses were 1.6 and 1.5 times as likely to be examined because of RAO during winter and spring, respectively, than they were during summer.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that RAO was more likely to be diagnosed in females, horses > or = 4 years old, and Thoroughbreds and that RAO has a seasonal distribution.

Risk factors for fecal shedding of Salmonella from horses in a veterinary teaching hospital

Identification of risk factors for horses shedding Salmonella in their feces helps identify patients at-risk of infection and protect the overall population through heightened biosecurity. Fecal samples from 230 hospitalized horses were cultured for Salmonella spp. Historical data were collected on 21 putative risk factors and assessed for association with the risk of a horse being culture positive using forwards stepwise logistic regression. Salmonella was isolated from 13 horses--most commonly from either the first (n=5) or second (n=4) sample collected. Only presenting complaint (confounded by age, breed and gender) was significantly (P < or = 0.05) associated with positive Salmonella-culture results. Analysis of residuals showed that the model was robust, but individual risk-factor estimates were changed by removal of outliers. Overall, presenting complaint (for example, lower-respiratory-tract disease) was the most important indicator of culture status.

Clinical signs, evaluation of bronchoalveolar lavage fluid, and assessment of pulmonary function in horses with inflammatory respiratory disease

OBJECTIVE

To evaluate the association among clinical signs, results of cytologic evaluation of bronchoalveolar lavage (BAL) fluid, and measures of pulmonary function in horses with inflammatory respiratory disease.

ANIMALS

9 healthy horses, 5 horses with inflammatory airway disease (IAD), and 9 horses with chronic obstructive pulmonary disease (COPD).

PROCEDURES

Clinical examination, lung function tests, and BAL were performed on each horse.

RESULTS

Standard lung mechanics of horses with exacerbated COPD differed significantly from those of healthy horses; however, there were few differences among horses with IAD, horses with COPD during remission, and healthy horses. Most variables for forced expiration (FE) in horses with COPD or IAD differed significantly from those for healthy horses. Results of clinical examination had low to moderate sensitivity and predictive values for a diagnosis of COPD (range, 67 to 80%). Results of FE tests had high sensitivity, specificity, and predictive values for a diagnosis of COPD (79 to 100%), and results of standard lung mechanics tests had low sensitivity and predictive values (22 to 69%). Percentage of neutrophils in BAL fluid was highly sensitive (100%) but moderately specific (64%) for a diagnosis of COPD.

CONCLUSIONS AND CLINICAL RELEVANCE

Clinical examination is moderately accurate for establishing a diagnosis of COPD. Forced expiration tests can specifically detect early signs of airway obstruction in horses with COPD and IAD that may otherwise be inapparent. Cytologic evaluation of BAL fluid allows early detection of inflammatory respiratory disease, but it is not specific for COPD.

Forced expiration: a test for airflow obstruction in horses

The purpose of this study was to assess whether our method of inducing forced expiration detects small airway obstruction in horses. Parameters derived from forced expiratory flow-volume (FEFV) curves were compared with lung mechanics data obtained during spontaneous breathing in nine healthy horses, in three after histamine challenge, and in two with chronic obstructive pulmonary disease (COPD) pre- and posttherapy with prednisone. Parameters measured in the healthy horses included forced vital capacity (FVC = 41.6 +/- 5.8 liters; means +/- SD) and forced expiratory flow (FEF) at various percentages of FVC (range of 20.4-29.7 l/s). Histamine challenge induced a dose-dependent decrease in FVC and FEF at low lung volume. After therapy, lung function of the two COPD horses improved to a point where one horse had normal lung mechanics during tidal breathing; however, FEF at 95% of FVC (4.9 l/s) was still decreased. We concluded that FEFV curve analysis allowed the detection of induced or naturally occurring airway obstruction.

Blood gas, plasma lactate and bronchoalveolar lavage cytology analyses in racehorses with respiratory disease

The purpose of this study was to evaluate the relationship between bronchoalveolar lavage (BAL) cytology, arterial blood gases and plasma lactate concentration during a standardised treadmill test (STT) in racehorses with small-airway inflammation (SAI), or exercise-induced pulmonary haemorrhage (EIPH). Sixteen Thoroughbred and 20 Standardbred actively racing racehorses, were divided into a control group (n = 10), EIPH group (n = 13) and SAI group (n = 13). Each STT consisted of a 2 min trot at 4 m/s followed by 5 x 1 min, incremental speed steps (6, 8, 10, 11 and 12 m/s) at 10% incline for Thoroughbred and 5% for Standardbred horses, followed by a 15 min recovery period. Blood was collected via a transverse facial artery catheter at the end of each step. Total nucleated cell count of bronchoalveolar lavage fluid (BALF) collected from horses with EIPH was significantly higher than controls. Neutrophil count and percentage in BALF collected pre-STT from horses with SAI were significantly higher than controls. Horses with EIPH or SAI exhibited a more severe exercise-induced arterial hypoxaemia than control horses during the first 4 steps of the STT (P < 0.001). Poorly performing horses were more severely hypercapnic than control horses during the STT recovery period (P < 0.05). Five and 15 min post exercise, horses with SAI and EIPH had higher blood lactate and lower blood bicarbonate concentrations than control horses (P < 0.05). The results of this study suggest that lung ventilation-perfusion mismatch may be more severe in horses with respiratory disease. BALF of horses with SAI and EIPH was characterised by neutrophilic and lymphocytic inflammation, respectively. Very few parameters were significantly different between groups of good and poor performers.

Adrenal insufficiency in a neonatal foal

A 3-day-old female Pinto was admitted with profuse watery diarrhea and severe hypovolemic shock. After 1 week of intensive care, the foal developed seizures associated with profound serum electrolyte abnormalities suggestive of hypoadrenocorticism. Treatment with prednisone and isotonic saline (0.9% NaCl) solution led to prompt clinical response. Premature withdrawal of prednisone resulted in relapse of clinical signs. A diagnosis of adrenal insufficiency was made on the basis of clinical signs, electrolyte abnormalities, low baseline cortisol concentration, and lack of response to administration of exogenous adrenocorticotropin. Two months later, adrenocortical function was normal and the foal was doing well clinically. Clinical signs of acute adrenal insufficiency in neonatal foals can be confused with other conditions, such as septicemia, enteritis, and ruptured urinary bladder. A persistently low serum sodium-to-potassium ratio associated with CNS malfunction should warrant investigation of adrenal gland function. Acute hypoadrenocorticism in foals may be reversible.

Listeria monocytogenes and Escherichia coli septicemia and meningoencephalitis in a 7-day-old llama

Listeria monocytogenes and Escherichia coli were isolated from blood collected on presentation and tissues samples taken postmortem. Listeria monocytogenes was isolated from cerebrospinal fluid collected antemortem. The importance of passive transfer of immunity, the subtlety of neurologic signs in early meningitis, and considering blood-CSF penetration in antimicrobial selection are discussed.

Primary hyperparathyroidism with osteodystrophia fibrosa of the facial bones in a pony

A 17-year-old pony mare was admitted for evaluation of progressive enlargement of the facial bones during the preceding 9 months. Laboratory testing revealed that the pony had hypercalcemia, hypophosphatemia, high urinary fractional excretion of phosphorus, and high serum concentration of intact parathyroid hormone (185.1 pmol/L; reference range, 0.25 to 2.0 pmol/L). On the basis of these findings, a diagnosis of primary hyperparathyroidism was made by ruling out nutritional secondary hyperparathyroidism, chronic renal disease, and pseudohyperparathyroidism resulting from neoplasia. Although primary hyperparathyroidism is best treated by surgical removal of the affected parathyroid gland, the owners declined surgical exploration of the neck in this pony. Because of the poor prognosis, the pony was euthanatized. A functional lesion of the parathyroid tissue was not located on necropsy or histologic examination. Difficulty localizing and grossly identifying parathyroid tissue in horses complicates definitive diagnosis and treatment of primary hyperparathyroidism.