Effect of stabling on bronchoalveolar cells obtained from normal and COPD horses

Influence of climatic changes on respiratory health in a teaching herd of outdoor-housed horses

Horses maintained outdoors may experience a lower-allergenic environment compared to their stabled counterparts. This study hypothesizes that climatic changes in southern Brazil can influence respiratory status. To test this hypothesis, we evaluated the lower airways of 17 horses from a teaching herd in southern Brazil, maintained outdoors, during winter, spring, and summer. Except for one mare with a history of severe asthma, all horses were considered healthy and underwent a physical examination. Airway endoscopic evaluation included scoring for tracheal mucus (0-5) and bronchial septum thickness (1-5). Bronchoalveolar lavage fluid (BALF) was collected at three time points, while bronchial septum biopsies were performed during spring and summer for airway epithelial investigation. Data analysis involved repeated measures ANOVA and Wilcoxon tests (p < 0.05). Tracheal mucus score and septal thickness did not differ across investigation periods. In BALF cytology, the mean percentage of neutrophils was higher in spring than summer (7.9 ± 13.4 % vs. 4.5 ± 11.7 %, P = 0.037), and eosinophil count was higher in winter than spring (0.64 ± 1.29 % vs. 0.03 ± 0.13 %, P = 0.034) and summer (0.64 ± 1.29 % vs. 0.14 ± 0.60 %, P = 0.023). Histopathological observations showed no differences between time points, and no correlations were observed with BALF analyses (P > 0.05). This study demonstrates that, even in an outdoor environment, horses' airways exhibit cytological modifications associated with different seasons, indicating a need for deeper investigation; endobronchial biopsy did not contribute to the clinical diagnosis.

Bilateral bronchoalveolar lavage cytology profiles in a warmblood horse population during a 1-year period

BACKGROUND

Bronchoalveolar lavage (BAL) cytology results from 1 lung might not be representative of both lungs.

OBJECTIVES

To determine whether the lung site sampled would influence the horse's BAL cytology profile, and if a pooled BAL sample would be superior with regard to BAL cytology diagnosis in a cohort of healthy and subclinical asthmatic warmblood horses.

ANIMALS

Fifty-nine horses in 2021 and 70 horses in 2022, the follow-up included 53 of the same in each year.

METHODS

A cross-sectional study with follow-up included BAL cytology samples from individual lungs and from pooled BAL samples. The BAL samples were enumerated and differential cell count were applied to categorize the horses as control or with airway inflammation (AI).

RESULTS

Bronchoalveolar lavage mast cell count was higher in left lung compared to right lung (2021; median 1.6 [range, 0.6-3.3] vs 1.2 [0.7-1.5] P = .009, 2022; median 3.1 [2.1-4.2] vs 2.4 [1.7-3.4], P < .001) and compared to pooled samples (2022; median 2.6 [1.7-3.7], P < .001). Between year 2021 and 2022, 17 of the horses had changes in BAL cytology from control to AI or vice versa.

CONCLUSIONS AND CLINICAL IMPORTANCE

Pooled BAL sample was the least reliable for detecting AI, and was not representative of the overall lung condition.

A CONSORT-guided, randomized controlled clinical trial of nebulized administration of dexamethasone and saline on lower airway cytokine mRNA expression in horses with moderate asthma

BACKGROUND

Nebulized administration of dexamethasone on cytokine regulation in horses with moderate asthma has not been investigated.

OBJECTIVE

To investigate the changes in expression of inflammatory cytokine mRNA after nebulized administration of dexamethasone treatment of horses with moderate asthma.

ANIMALS

Horses with naturally occurring moderate asthma (n = 16) and healthy control horses (n = 4). All horses were kept in a dusty environment during the study.

METHODS

Prospective, parallel, randomized, controlled, blinded clinical trial. Blood endogenous cortisol, tracheal mucus, and bronchoalveolar lavage (BAL) were sampled before and after 13 days treatment with either nebulized administration of dexamethasone (15 mg once daily) or 0.9% saline (3 mL). Treatment groups were randomly allocated via randomization function (Microsoft Excel). Amplification of target mRNA in BAL fluid (IL-1β, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12, IL-17, IL-23, IFN-γ, Eotaxin-2, and TNF-α) was achieved by qPCR, and the relative expression software tool was used to analyze BAL inflammatory cytokine mRNA.

RESULTS

Horses treated with nebulized administration of dexamethasone had increased relative expression of IL-5 (1.70-fold), IL-6 (1.71-fold), IL-17 (3.25-fold), IL-12 (1.66-fold), and TNF-α (1.94-fold), and decreased relative expression of IL-23 (1.76-fold; P = .04) in samples collected on Day 14, in comparison to samples collected on Day 0 (all P < .05). Horses treated with nebulized administration of saline had no significant difference in the relative expression of any gene (all P > .05).

CONCLUSIONS AND CLINICAL IMPORTANCE

Nebulized administration of dexamethasone was associated with increased expression of inflammatory cytokine mRNA. There was no improvement in inflammatory airway cytology associated with either dexamethasone or saline treatment.

Lipid species profiling of bronchoalveolar lavage fluid cells of horses housed on two different bedding materials

The lipidome of equine BALF cells has not been described. The objectives of this prospective repeated-measures study were to explore the BALF cells' lipidome in horses and to identify lipids associated with progression or resolution of airway inflammation. BALF cells from 22 horses exposed to two bedding materials (Peat 1-Wood shavings [WS]-Peat 2) were studied by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The effects of bedding on lipid class and species compositions were tested with rmANOVA. Correlations between lipids and cell counts were examined. The BALF cells' lipidome showed bedding-related differences for molar percentage (mol%) of 60 species. Whole phosphatidylcholine (PC) class and its species PC 32:0 (main molecular species 16:0_16:0) had higher mol% after Peat 2 compared with WS. Phosphatidylinositol 38:4 (main molecular species 18:0_20:4) was higher after WS compared with both peat periods. BALF cell count correlated positively with mol% of the lipid classes phosphatidylserine, sphingomyelin, ceramide, hexosylceramide, and triacylglycerol but negatively with PC. BALF cell count correlated positively with phosphatidylinositol 38:4 mol%. In conclusion, equine BALF cells' lipid profiles explored with MS-based lipidomics indicated subclinical inflammatory changes after WS. Inflammatory reactions in the cellular lipid species composition were detected although cytological responses indicating inflammation were weak.

Nebulized glycosylated caffeic acid phenylether ester attenuation of environmental particulate-induced airway inflammation in horses

The objective of this study was to determine the extent that nebulized glycosylated caffeic acid phenylether ester-4-O-alpha-D-glucopyranoside (G-CAPE) attenuates particulate-induced airway inflammation in healthy horses. Our hypothesis was that nebulization with G-CAPE would result in improved respiratory scores, higher arterial oxygen partial pressure, and less inflammatory airway infiltrates in horses with induced airway inflammation, compared with untreated controls. Five healthy adult horses were housed inside a climate controlled, closed barn on straw bedding and fed ad lib moldy grass hay for 16 days to induce airway inflammation. An experimental crossover study was performed in which animals were treated with 200 mg G-CAPE dissolved in 45 mL of 10% triethanolamine (G-CAPE group) or 45 mL of 10% triethanolamine (CONTROL group), and clinical respiratory scoring, arterial blood gases, and bronchoalveolar lavages (BALs) were collected at predetermined time points up to 24 h post nebulization. While the mean neutrophil percentage decreased in treated horses compared to controls (9.3 ± 2.0 and 16.9 ± 2.4, respectively) at 6 hours post treatment (t = 6 h), the difference did not achieve statistical significance (p = 0.1154). Blood gas analysis did not differ significantly between groups. There was a significant difference in the mean respiratory scores of G-CAPE-treated horses between baseline and at 1-h post treatment (from 3.2 ± 0.7 to 1.6 ± 0.7, p = 0.0013). This study demonstrates that a single nebulized dose of G-CAPE decreased clinical respiratory scores 1 h post administration and decreased BAL percentage of neutrophils 6 h post administration in horses with particulate induced airway inflammation. This compound shows promise as an anti-inflammatory and warrants further investigation.

Immunohistochemical Expression of Neurokinin-A and Interleukin-8 in the Bronchial Epithelium of Horses with Severe Equine Asthma Syndrome during Asymptomatic, Exacerbation, and Remission Phase

Severe equine asthma (EA) syndrome is a chronic obstructive disease characterized by exaggerated contraction, inflammation, and structural alteration of the airways in adult horses, when exposed to airborne molds and particulate material. However, little is known about the relationship between the degree and type of inflammation on one hand, and the severity of the disease and the response to treatment on the other. Furthermore, to date, very few studies evaluate the diagnostic value of histology and immunohistochemical features of endoscopic biopsies on subjects with severe equine asthma. To investigate the expression of two inflammatory markers (NKA and IL-8) before, during, and after the exacerbation of severe EA, a histological and immunohistochemical study was carried out on a series of biopsy samples collected by bronchoscopy from six EA-affected horses subjected to process exacerbation through environmental stimuli and then to pharmacological treatment. The application of a histological biopsy scoring system revealed a significant difference between control cases and the EA-affected horses in all experimental phases (asymptomatic, early exacerbation phase, late exacerbation phase, and remission phase). For immunohistochemistry (IHC), only the intensity of NKA positivity increases significantly between control horses and the EA horses at late exacerbation and remission phases. In EA-affected horses, a difference was detected by comparing histology between asymptomatic and remission phase, meanwhile, NKA and IL-8 showed no differences between the experimental phases. Based on these results we can assert that: (1) The endoscopic biopsies generate reliable and homogeneous samples in the entire bronchial tree; (2) the clinical improvement associated with treatment is characterized by a significant worsening of the histological findings; and (3) the NKA immunopositivity seems to increase significantly rather than decrease, as one would have expected, after pharmacological treatment. Further studies are necessary both to implement the number of samples and to use other markers of inflammation to characterize the potential role of cytokines in the diagnosis and therapeutic approach of severe equine asthma.

The Dynamics of Circulating Immune Complexes in Horses with Severe Equine Asthma

Simple Summary

Equine asthma syndrome is a cost-consuming equine respiratory disease of the lower airways in horses. Non-invasive biomarkers from blood or urine are sought. The aim of this study was to assess the circulating immune complexes (CICs) during the exacerbation and remission of an asthma episode—with and without additional treatment and the potential usefulness of CIC levels in the diagnosis, monitoring, and treatment progression. The control group, asthma group, and treated asthma group each contained six horses. The horses were kept in a dusty environment for seven days and then moved to an asthma-friendly environment for over three weeks (the treated group received injections of glucocorticoids). Blood was collected at baseline and on the 1st, 2nd, 3rd, 7th, 14th and 30th days. CICs measured in the time points did not show statistical differences. When CICs were analysed within the groups, there was a significant decrease in CIC in the treated group and a significant increase in CIC in the non-treated group on day 30. CIC did not support the diagnosis procedure of equine asthma syndrome, although it may help in monitoring patients with and without treatment. To the best of the authors’ knowledge, this is the first study to analyse the dynamics of CIC in equine asthma patients during an environmental challenge, remission, and treatment.

Abstract

Non-invasive diagnostic biomarkers of equine asthma syndrome (EAS) from blood or urine are sought. The aim of this study was to assess the absorbance of circulating immune complexes (CICs) during the exacerbation, remission, and treatment of an asthma episode and assess the potential usefulness of CIC levels in the diagnosis and monitoring of the disease. The control group, asthma group, and treated asthma group each contained six horses. Following an initial examination and group classification, the horses were kept in a dusty environment for seven days and then moved to an asthma-friendly environment for three weeks (the treated group received injections of glucocorticoids). Blood was collected at baseline and on the 1st, 2nd, 3rd, 7th, 14th and 30th days. CIC was measured using the modified Haskova method. The time points did not show significant statistical differences. There was a significant decrease in CIC in the treated group, and a significant increase in CIC in the non-treated group on day 30. CIC did not support the EAS diagnosis, although it may help in monitoring patients. To the best of the authors’ knowledge, this is the first study to analyse the dynamics of CIC during environmental challenge, remission, and treatment.

Effects of nebulized dexamethasone on the respiratory microbiota and mycobiota and relative equine herpesvirus-1, 2, 4, 5 in an equine model of asthma

Background

Prolonged exposure to environmental antigens or allergens elicits an immune response in both healthy horses and those with mild asthma. Corticosteroids often are used to treat lower airway inflammation.

Objective

To investigate the changes in equine herpesvirus (EHV)‐1,2,4,5 glycoprotein B gene expression and changes in respiratory bacterial and fungal communities after nebulized dexamethasone treatment of horses with asthma.

Animals

Horses with naturally occurring mild asthma (n = 16) and healthy control horses (n = 4).

Methods

Prospective, randomized, controlled, blinded clinical trial. Polymerase chain reaction amplification of EHV‐1,2,4,5 in bronchoalveolar lavage fluid, and 16S (microbiome) and ITS2 (mycobiome) genes with subsequent sequencing was performed on DNA extracted from nasal swabs and transendoscopic tracheal aspirates before and after 13 days treatment with nebulized dexamethasone (15 mg q24h) and saline (control).

Results

Nebulized dexamethasone treatment decreased microbial diversity; relative abundance of 8 genera in the upper respiratory tract were altered. For both the microbiota and the mycobiota, environment had a dominant effect over treatment. Alternaria, an opportunistic pathogen and allergen in humans recognized as a risk factor for asthma, asthma severity, and exacerbations, was increased with treatment. Treatment affected relative quantification of the equine gamma herpesviruses (EHV‐2 and ‐5); EHV‐2 DNA levels increased and those of EHV‐5 decreased.

Conclusions

Nebulized dexamethasone treatment affected the upper respiratory tract microbiota, but not the mycobiota, which was overwhelmed by the effect of a sustained dusty environment.

Efeitos da estabulação sobre o trato respiratório de equinos em dois tipos diferentes de camas e a pasto

RESUMO As afecções do sistema respiratório são a segunda causa de queda de desempenho e afastamento dos equinos do esporte ou trabalho, as quais estão atrás somente das desordens musculoesqueléticas. A estabulação e a alimentação à base de fenos predispõem os equinos à inalação de grande número de agentes irritantes às vias aéreas. No intuito de avaliar a influência dos tipos de cama utilizados em baias, estudaram-se três grupos de cinco equinos cada, durante 45 dias. Dois grupos foram mantidos em cocheiras com forrações diferentes à base de madeira (maravalha de pínus autoclavada-MA e serragem-SE) e o terceiro grupo permaneceu no pasto. Foram realizadas avaliações quinzenais, que incluíram exame físico, hemograma, hemogasometria e lavado broncoalveolar. Ao exame físico, notou-se a presença de tosse e espirros em animais do grupo SE. No lavado broncoalveolar, a contagem de células nucleadas totais apresentou maiores valores nos animais a pasto, seguido do grupo SE e, por último, o MA. Concluiu-se que as duas camas testadas neste estudo não apresentaram diferença com relação à capacidade irritativa das vias aéreas superiores no período analisado.

Increased leishmanicidal activity of alveolar macrophages from mature horses with mild equine asthma

ABSTRACT Alveolar macrophages (AMs) are an essential part of defense mechanisms within the lungs and their phagocytic activity is important for organ homeostasis. The phagocytic ability of AMs obtained from bronchoalveolar lavage from 17 mature mixed-breed pleasure horses (8 healthy and 9 diagnosed with mild equine asthma) was studied through assays with Leishmania (Viannia) braziliensis promastigotes, which enabled the calculation of a phagocytic index (PI) and a survival index (SI). Results indicate that phagocytic activity of AMs in asthma affected horses is similar to healthy horses, while leishmanicidal activity is significantly increased in horses with asthma.

Lower Airway Disease in the Athletic Horse

The airways are the first part of the pathway in the oxygen transport chain that is critical to excellent athletic performance, and the lower airways are considered the final gatekeeper before oxygen enters the blood and carbon dioxide exits. Horses are blessed with large airways and lungs that allow them to be superb athletes, but the down side of this largesse on the part of evolution is that unless they are truly elite athletes they may withstand noninfectious disease of the lower respiratory tract for months to years before the owner or trainer notices. The two conditions of the lower respiratory tract that affect the athletic horse during exercise are exercise-induced pulmonary hemorrhage and inflammatory airway disease. The former may be considered, at least at the onset, as a problem of physiology rather than a disease, and the latter is a disease primarily of domestication: both are widespread among the athletic horse population and account for an impressive number of horses that fail to perform to their potential. Because of the high demands for oxygen in the athletic horse, even minor insults to the oxygen-carrying capacity of the body can affect performance, so it is of critical importance to keep the lungs as healthy as possible.

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.

Effect of antigen challenge on dynamics of CD62P and CD41/61 expression on platelets in horses with recurrent airway obstruction (RAO)

Recurrent airway obstruction (RAO), also known as heaves, is an allergic respiratory condition that develops in horses following an exposure to aeroallergens in hay and straw. This is manifested by airway hyperreactivity, inflammation, bronchoconstriction, as well as a leukocyte and platelet infiltration into the airways. Platelet activation and an increase in circulating platelet-leukocyte aggregates may lead to airway remodeling. The aim of this study was to explore the effect of seven-day antigen challenge on dynamics of platelet indices and CD41/61 and CD62 P expression on platelets in horses with RAO. Ten RAO-affected horses and ten healthy horses were included in this study. All horses were exposed to 7 days hay and straw challenge. Blood samples were collected prior to the challenge (Pre-challenge) and 1, 2, 3, 7 and 14 days after the initiating the antigen challenge. Blood samples were obtained to determine the platelet count (PLT), mean platelet volume (MPV) and platelet large cell ratio (P-LCR). Expression of CD62 P and CD41/61 was detected by flow cytometry on activated platelets. Antigen challenge resulted in a significant gradual decrease of PLT in RAO horses, but not in controls. MPV and P-LCR in control and RAO-affected horses remained unchanged after antigen challenge. The expression of CD62 P and CD41/61 in RAO horses was significantly higher compared to control horses. The antigen challenge resulted in an increase expression of CD62 P and CD41/61 on the platelets of RAO-affected horses, while did not lead to significant changes in the control group. An increased expression of CD62 P and CD41/61 indicates platelet activation what may contribute to the formation of platelet aggregates in their respiratory system.

Phagocytosis, bacterial killing, and cytokine activation of circulating blood neutrophils in horses with severe equine asthma and control horses

OBJECTIVE To evaluate in vitro phagocytosis and bactericidal activity of circulating blood neutrophils in horses with severe equine asthma and control horses and to determine whether circulating blood neutrophils in horses with severe equine asthma have an increase in expression of the proinflammatory cytokine tumor necrosis factor (TNF)-α and the chemokine interleukin (IL)-8 and a decrease in expression of the anti-inflammatory cytokine IL-10 in response to bacteria. ANIMALS 6 horses with severe equine asthma and 6 control horses. PROCEDURES Circulating blood neutrophils were isolated from horses with severe equine asthma and control horses. Phagocytosis was evaluated by use of flow cytometry. Bactericidal activity of circulating blood neutrophils was assessed by use of Streptococcus equi and Streptococcus zooepidemicus as targets, whereas the cytokine mRNA response was assessed by use of a quantitative PCR assay. RESULTS Circulating blood neutrophils from horses with severe equine asthma had significantly lower bactericidal activity toward S zooepidemicus but not toward S equi, compared with results for control horses. Phagocytosis and mRNA expression of TNF-α, IL-8, and IL-10 were not different between groups. CONCLUSIONS AND CLINCAL RELEVANCE Impairment of bactericidal activity of circulating blood neutrophils in horses with severe equine asthma could contribute to an increased susceptibility to infections.

Glucocorticosteroids administration is associated with increased regulatory T cells in equine asthmatic lungs

Recurrent inflammation in severe equine asthma causes a remodeling of the airways leading to incompletely reversible airway obstruction. Despite the improvement of clinical signs and lung function with glucocorticoids (GC), inflammation, translated by an increased percentage of neutrophils, persists in the airways. Regulatory T cells (Treg) have been shown to have anti-inflammatory properties and play an important role in balancing the immune response by suppressing effector lymphocyte activity. However, interactions between Treg, neutrophils and glucocorticosteroids in vivo are unclear, particularly in asthma. Furthermore, the effects of GC on Treg in the airway of asthmatic horses have not been investigated. We hypothesized that horses with severe asthma display a decreased population of pulmonary Treg when compared to heathy controls, and that treatment with GC lead to an increased pulmonary Treg cell population only in affected horses. Using lung function measurements and flow cytometry with surface antigens CD4 and FoxP3, we investigated Treg in airway luminal cells obtained by bronchoalveolar lavage fluid (BALF) from 6 asthmatic horses in exacerbation of the disease and 6 aged-match controls, kept in the same environment, before and following a 2-week treatment with dexamethasone. Results showed that the number of Treg increases only in the lungs of asthmatic horses following GC therapy, despite continued presence of increased numbers of neutrophils. Our results support the complexity of the interaction between Treg, neutrophils and GC.

Bioavailability and tolerability of nebulised dexamethasone sodium phosphate in adult horses

BACKGROUND

Nebulisation of the injectable dexamethasone sodium phosphate (DSP) would offer an inexpensive way of delivering a potent corticosteroid directly to the lungs of horses with asthma. However, this approach would be advantageous only if systemic absorption is minimal and if the preservatives present in the formulation do not induce airway inflammation.

OBJECTIVE

To investigate the bioavailability of nebulised DSP and determine whether it induces airway inflammation or hypothalamic-pituitary-adrenal (HPA) axis suppression in healthy adult horses.

STUDY DESIGN

Randomised crossover experiment.

METHODS

Dexamethasone sodium phosphate was administered to six healthy adult horses at a dose of 5 mg q. 24 h for 5 days via nebulised, or intravenous (i.v.) routes. Plasma dexamethasone concentrations were measured by UPLC/MS-MS to calculate bioavailability. Cytological examination of bronchoalveolar fluid was performed at baseline and after the last dose of DSP. A validated chemiluminescent immunoassay was used to measure basal serum cortisol concentrations.

RESULTS

After nebulisation to adult horses, dexamethasone had a mean (±s.d.) maximum plasma concentration of 0.774 ± 0.215 ng/mL and systemic bioavailability of 4.3 ± 1.2%. Regardless of route of administration, there was a significant decrease in the percentage of neutrophils in bronchoalveolar lavage fluid over time. During i.v. administration, basal serum cortisol concentration decreased significantly from baseline to Day 3 and remained low on Day 5. In contrast, basal serum cortisol concentration did not change significantly during administration via nebulisation.

MAIN LIMITATIONS

Small sample size and short period of drug administration.

CONCLUSIONS

Dexamethasone sodium phosphate administered via nebulisation had minimal systemic bioavailability and did not induce lower airway inflammation or HPA axis suppression in healthy horses.

Pulmonary Remodeling in Equine Asthma: What Do We Know about Mediators of Inflammation in the Horse?

Equine inflammatory airway disease (IAD) and recurrent airway obstruction (RAO) represent a spectrum of chronic inflammatory disease of the airways in horses resembling human asthma in many aspects. Therefore, both are now described as severity grades of equine asthma. Increasing evidence in horses and humans suggests that local pulmonary inflammation is influenced by systemic inflammatory processes and the other way around. Inflammation, coagulation, and fibrinolysis as well as extracellular remodeling show close interactions. Cytology of bronchoalveolar lavage fluid and tracheal wash is commonly used to evaluate the severity of local inflammation in the lung. Other mediators of inflammation, like interleukins involved in the chemotaxis of neutrophils, have been studied. Chronic obstructive pneumopathies lead to remodeling of bronchial walls and lung parenchyma, ultimately causing fibrosis. Matrix metalloproteinases (MMPs) are discussed as the most important proteolytic enzymes during remodeling in human medicine and increasing evidence exists for the horse as well. A systemic involvement has been shown for severe equine asthma by increased acute phase proteins like serum amyloid A and haptoglobin in peripheral blood during exacerbation. Studies focusing on these and further possible inflammatory markers for chronic respiratory disease in the horse are discussed in this review of the literature.

Development of a Semiquantitative Histological Score for the Diagnosis of Heaves Using Endobronchial Biopsy Specimens in Horses

Background

Remodeling of the peripheral airways persists during the asymptomatic phase of heaves. Assessing the histology of large bronchi could facilitate the diagnosis of heaves during remission of the disease.

Hypothesis

Airway inflammation and remodeling in endobronchial biopsy (EBB) specimens differentiate horses with heaves from controls, independently of their clinical status (exacerbation or remission).

Animals

Fourteen healthy horses and 24 horses with heaves.

Methods

A 14‐point scoring system assessing central bronchial wall inflammation and remodeling was developed. The score was validated by 2 pathologists using specimens obtained from 18 horses (6 controls, 6 with heaves exacerbation, and 6 with heaves remission) in which lung function had been assessed with impulse oscillometry. Clinical and research application of the score was evaluated using biopsy specimens obtained from 20 additional horses (8 controls, 6 with heaves exacerbation, and 6 with heaves remission).

Results

The score was repeatable (interclass correlation coefficient = 69%). It differentiated horses with heaves in exacerbation (mean ± SD: 6.2 ± 2.2) from those in remission (4.0 ± 1.0) and controls (3.6 ± 1.7, P < 0.0001). The histological scores of horses with heaves correlated with the ratio of respiratory resistance (R) at 5 and 10 Hz (R₅ : R₁₀ ratio, r = 0.65, P = 0.03), a parameter assessing airway obstruction.

Conclusions and Clinical Significance

The proposed histological scoring system correlates with the degree of airway obstruction measured by impulse oscillometry. However, it does not discriminate horses with heaves in remission from controls. Evaluation of EBB specimens might be considered in future research and clinical studies of respiratory diseases in horses.

Tracheobronchoscopic Assessment of Exercise-Induced Pulmonary Hemorrhage and Airway Inflammation in Barrel Racing Horses

Background

Poor performance is often suspected to be associated with EIPH in barrel racing horses; however, there are no published reports of EIPH for this discipline. The prevalence of EIPH in barrel racing horses is also unknown.

Objectives

This study was performed to determine the prevalence of EIPH and signs of airway inflammation in barrel racing horses under normal racing conditions in Alberta.

Animals

About 170 barrel racing horses.

Methods

Observational cross‐sectional study. Tracheobronchoscopic examinations were performed at least 30 minutes postrace. Video recordings were scored off‐site independently by two observers for EIPH and tracheal mucus accumulation (TMA). Horses with an EIPH score ≥2 were not assessed for TMA. Interobserver agreement was calculated by weighted κ statistics. Run times, environmental variables, and clinical information were also recorded for analysis.

Results

77/170 (45.3%) of horses examined showed evidence of EIPH (grade ≥ 1). Interobserver agreement was 0.94. 140/141 (99.3%) of horses assessed for TMA showed evidence of tracheal mucus accumulation (grade ≥ 1) with 104/141 (73.8%) having a TMA score ≥ 2. Interobserver agreement was 0.73. A weak positive association was found between EIPH scores and average run speed, the presence of cough at rest reported by the riders, increased recovery time, exercise intolerance, and outdoor pattern.

Conclusions and clinical importance

The high prevalence of EIPH observed in the sampled population indicates that barrel racing induces substantial stress on the lungs. The presence of EIPH did not impact negatively on performance. Factors such as environmental dust and frequent traveling might have contributed to the high prevalence of TMA observed.

Update on noninfectious inflammatory diseases of the lower airway

Inflammatory airway disease and recurrent airway obstruction are 2 nonseptic diseases of the equine respiratory system with a shared cause of exposure to particulate matter. They appear to occupy 2 ends of a spectrum of disease, but are differentiated by history, clinical signs, and response to treatment. Diagnosis can be made by sampling of respiratory fluids and lung function testing. Treatment consists of environmental modification and pharmacologic treatment with systemic or inhaled corticosteroids and bronchodilators.

Asthma "of horses and men"--how can equine heaves help us better understand human asthma immunopathology and its functional consequences?

Animal models have been studied to unravel etiological, immunopathological, and genetic attributes leading to asthma. However, while experiments in which the disease is artificially induced have helped discovering biological and molecular pathways leading to allergic airway inflammation, their contribution to the understanding of the causality of the disease has been more limited. Horses naturally suffer from an asthma-like condition called "heaves" which presents sticking similarities with human asthma. It is characterized by reversible airway obstruction, airway neutrophilic inflammation, and a predominant Th2 immune response. This model allows one to investigate the role of neutrophils in asthma, which remains contentious, the regulation of chronic neutrophilic inflammation, and their possible implication in pulmonary allergic responses. Furthermore, the pulmonary remodeling features in heaves closely resemble those of human asthma, which makes this model unique to investigate the kinetics, reversibility, as well as the physiological consequences of tissue remodeling. In conclusion, heaves and asthma share common clinical presentation and also important immunological and tissue remodeling features. This makes heaves an ideal model for the discovery of novel pathways implicated in the asthmatic inflammation and associated tissue remodeling.

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.

Recurrent airway obstruction: a review

Recurrent airway obstruction is a widely recognised airway disorder, characterised by hypersensitivity-mediated neutrophilic airway inflammation and lower airway obstruction in a subpopulation of horses when exposed to suboptimal environments high in airborne organic dust. Over the past decade, numerous studies have further advanced our understanding of different aspects of the disease. These include clarification of the important inhaled airborne agents responsible for disease induction, improving our understanding of the underlying genetic basis of disease susceptibility and unveiling the fundamental immunological mechanisms leading to establishment of the classic disease phenotype. This review, as well as giving a clinical overview of recurrent airway obstruction, summarises much of the work in these areas that have culminated in a more thorough understanding of this debilitating disease.

Infectious risk factors and clinical indicators for tracheal mucus in British National Hunt racehorses

REASONS FOR PERFORMING STUDY

Many studies of respiratory disease in racehorses have focused on a combination of increased tracheal mucus and airway neutrophilia. Examination of each component separately should provide further insight into this condition.

OBJECTIVES

To identify infectious risk factors for endoscopically visible tracheal mucus in National Hunt racehorses.

STUDY DESIGN

A 2 year prospective longitudinal study.

METHODS

Monthly quantitative bacteriological examinations of tracheal wash samples and viral serological examinations were conducted. Risk factors for 'small amounts of mucus' (mucus score = 1/3) and 'increased mucus' (score ≥2/3) were identified.

RESULTS

There were increased odds of small amounts of mucus when both Streptococcus zooepidemicus and nonhaemolytic streptococci (NHS) were isolated (odds ratio [OR] 2.6; 95% confidence interval [CI] 1.5-4.6; P<0.001) but not when either species was isolated in the absence of the other. Increased odds of increased mucus were associated with the isolation of either S. zooepidemicus (OR 5.6; 95% CI 1.2-25.9; P = 0.03) or NHS (OR 3.7; 95% CI 1.2-11.6; P = 0.02), with an increased effect when both were isolated together (OR 12.5; 95% CI 3.7-41.6; P<0.001). Approximately 6-fold increased odds of small amounts of mucus were associated with the first 3 months in training (OR 6.3; 95% CI 2.0-19.4; P<0.001) and 3-fold increased odds of increased mucus associated with the first 6 months in training (OR 2.9; 95% CI 1.3-6.4; P = 0.01). Coughing at exercise and increased serous nasal discharge were specific but insensitive indicators of increased mucus.

CONCLUSIONS

Associations with S. zooepidemicus corroborate previous research, but an independent effect of NHS has not previously been reported. The possibility that there are individual pathogenic species within this group should be considered. Further work is required to identify S. zooepidemicus subtypes and NHS species associated with disease. Closer monitoring of the respiratory health of horses entering training for the first time is likely to be valuable.

Local airborne particulate concentration is associated with visible tracheal mucus in Thoroughbred racehorses

REASON FOR PERFORMING STUDY

Accumulations of tracheal mucus assessed by endoscopic examination are associated with poor performance in racehorses. The air quality in horses' stalls may contribute to this visible tracheal mucus.

OBJECTIVES

To determine whether the concentration and number of airborne particulates in stalls are associated with visible accumulations of tracheal mucus and with the number of inflammatory cells in tracheal aspirates.

METHODS

We studied 107 racehorses from 3 stables, in 3 different months, and measured airborne particulate matter 3 times daily in each of the stalls. On each monthly visit, horse airways were examined endoscopically and assigned a mucus score, and tracheal lavage was performed. Bivariate procedures, general estimating equations and linear mixed models were applied to estimate the association between PM and the presence of accumulations of mucus and number of inflammatory cells.

RESULTS

Stable, stall, month and PM were all significantly associated with the presence of accumulations of tracheal mucus, which had an overall prevalence of 67%. The odds of horses having visible accumulation of mucus were increased when horses occupied enclosed stables or stalls with higher particulate concentrations, and when concentrations of larger particles (≤ 10 µm in diameter) were elevated. Sixty-eight percent of tracheal wash samples contained more than 20% neutrophils. Increased numbers of neutrophils were associated with the concentration of smaller particles (≤ 2.5 µm in diameter).

POTENTIAL RELEVANCE

Careful consideration of stable construction and management practices focused on maintaining the lowest possible dust concentrations throughout the day should reduce the prevalence of visible accumulations of tracheal mucus, potentially improving racing performance.

Heaves, an asthma-like disease of horses

Animal models have been developed to investigate specific components of asthmatic airway inflammation, hyper-responsiveness or remodelling. However, all of these aspects are rarely observed in the same animal. Heaves is a naturally occurring disease of horses that combines these features. It is characterized by stable dust-induced inflammation, bronchospasm and remodelling. The evaluation of horses during well-controlled natural antigen exposure and avoidance in experimental settings allows the study of disease mechanisms in the asymptomatic and symptomatic stages, an approach rarely feasible in humans. Also, the disease can be followed over several years to observe the cumulative effect of repeated episodes of clinical exacerbation or to evaluate long-term treatment, contrasting most murine asthma models. This model has shown complex gene and environment interactions, the involvement of both innate and adaptive responses to inflammation, and the contribution of bronchospasm and tissue remodelling to airway obstruction, all occurring in a natural setting. Similarities with the human asthmatic airways are well described and the model is currently being used to evaluate airway remodelling and its reversibility in ways that are not possible in people for ethical reasons. Tools including antibodies, recombinant proteins or gene arrays, as well as methods for sampling tissues and assessing lung function in the horse are constantly evolving to facilitate the study of this animal model. Research perspectives that can be relevant to asthma include the role of neutrophils in airway inflammation and their response to corticosteroids, systemic response to pulmonary inflammation, and maintaining athletic capacities with early intervention.

Evaluation of variations in bronchoalveolar lavage fluid in horses with recurrent airway obstruction

OBJECTIVE

To determine variations in cytologic counts of bronchoalveolar lavage (BAL) fluid attributable to month of collection, first and second aliquots, and left and right lung sites in horses with recurrent airway obstruction (RAO).

ANIMALS

5 horses with RAO and 5 healthy horses without respiratory tract disease.

PROCEDURES

Horses were housed in a stable for 5 months prior to and throughout the study. Bronchoalveolar lavage fluid was collected from the right and left lung of each horse 3 times at monthly intervals (February, March, and April). Each BAL fluid collection was performed by use of 2 incremental instillations of 250 mL of isotonic saline (0.9% NaCl) solution in the same bronchial site. Analysis of BAL fluid included volume of BAL fluid recovered, a CBC, and differential cytologic counts.

RESULTS

Volume of BAL fluid recovered and cytologic counts did not differ in horses with RAO across time or between right and left lungs, except for the number of mast cells. Horses with RAO had significantly lower volumes of BAL fluid recovered, significantly lower percentages of macrophages and lymphocytes, and significantly higher percentages of neutrophils than did healthy horses. Despite individual variation, all horses with RAO had > 25% neutrophils throughout the study period.

CONCLUSIONS AND CLINICAL RELEVANCE

Despite variation among horses, BAL fluid cytologic counts were repeatable over short and long periods and samples can be used for longitudinal studies as a diagnostic tool of pulmonary inflammation in horses with RAO.

Cytokine mRNA expression of pulmonary macrophages varies with challenge but not with disease state in horses with heaves or in controls

Heaves in horses is characterized by lower airway neutrophilic inflammation, and reversible airflow obstruction. Pulmonary macrophages contribute to the inflammation observed in a number of human and animal pulmonary diseases, and it has been postulated that they are responsible for the neutrophilic inflammation present in heaves by the release of cytokines and chemokines. To test this hypothesis, the mRNA expression of TNF-α, IL-1β, IL-8, and MIP-2 by macrophages isolated from bronchoalveolar lavage cells was quantified using real-time RT-PCR in horses with heaves (n-6) and controls (n-6). Animals were studied after being pastured for 3 months to induce clinical remission of heaves, and after 24h, and 9 days of a continuous natural antigen challenge consisting of hay feeding and straw bedding. The study was performed during 2 consecutive summers, when 3 horses with heaves and 3 control horses were evaluated. As expected, airway obstruction developed with the challenge only in horses with heaves, while airway neutrophilia was observed in both groups of horses. Stabling resulted in an increased expression of IL-8/ß-actin and MIP-2/ß-actin after 24h of stabling in both groups of horses. Further analyses revealed that compared to pasture, the expression of these chemokines was significantly increased after 24h of stabling only in Year 1, while the IL-8 expression was significantly decreased at 9 days in Year 2. No significant group, time, or year differences in IL-1β/ß-actin and TNF-α/ß-actin ratio were observed. The expression of IL-1β was strongly correlated with neutrophil percentages, although at different time points in the two study-years. These results suggest that alveolar macrophages can contribute to the airway inflammation resulting from stabling in horses by the release of IL-8 and MIP-2, but that the release of these chemokines is unlikely to be responsible for the marked airway neutrophilia observed in heaves. The variable expression of IL-8 and MIP-2 by alveolar macrophages between the two-study years are additional novel findings highlighting the complexity of the inflammatory pathways associated with airway inflammation and the importance of evaluating concurrently horses with heaves and controls to ensure identical environmental challenges.

Differential association of MUC5AC and CLCA1 expression in small cartilaginous airways of RAO-affected and control horses

REASONS FOR PERFORMING STUDY

Airway mucus accumulation is associated with indoor irritant and allergen exposure in horses with recurrent airway obstruction (RAO). Epidermal growth factor receptor (EGFR) and a chloride channel (calcium activated, family member 1; CLCA1) are key signalling molecules involved in mucin gene expression.

OBJECTIVES

We hypothesised that exposure to irritants and aeroallergens would lead to increased expression of the mucin gene eqMUC5AC and increased stored mucosubstance in the airways of RAO-affected horses, associated with increased neutrophils and CLCA1 and EGFR mRNA levels.

METHODS

We performed quantitative RT-PCR of eqMUC5AC, CLCA1 and EGFR; volume density measurements of intraepithelial mucosubstances; and cytological differentiation of intraluminal inflammatory cells in small cartilaginous airways from cranial left and right and caudal left and right lung lobes of 5 clinically healthy and 5 RAO-affected horses that had been exposed to indoor stable environment for 5 days before euthanasia.

RESULTS

Neutrophils were increased in RAO-affected horses compared to clinically healthy controls. EqMUC5AC mRNA levels were positively correlated with both CLCA1 and EGFR mRNA levels in RAO-affected horses but only with CLCA1 in controls. The relationship between eqMUC5AC and CLCA1 differed in the 2 groups of horses with RAO-affected animals overexpressing CLCA1 in relation to eqMUC5AC.

CONCLUSIONS

These data implicate CLCA1 as a signalling molecule in the expression of eqMUC5AC in horses but also suggest differential regulation by CLCA1 and EGFR between horses with RAO and those with milder degrees of airway inflammation.

Airway inflammation in Michigan pleasure horses: prevalence and risk factors

REASONS FOR PERFORMING STUDY

Although subclinical airway inflammation is thought to be common in horses, there is little information on its prevalence and none on risk factors.

OBJECTIVE

To determine the prevalence and risk factors for an increased number of inflammatory cells and for mucus accumulation in the trachea of pleasure horses.

METHODS

Horses (n = 266) in stables (n = 21) in Michigan were examined endoscopically, once in winter and once in summer 2004. Visible tracheal mucoid secretions were graded 0-5 and inflammatory cell numbers counted in a tracheal lavage sample. Information collected about each horse included age, gender, presence of cough, percent time indoors and source of roughage. The repeated measures were analysed by generalised estimating equations and linear mixed models.

RESULTS

Horses eating hay, especially from round bales, had the most neutrophils, whereas horses feeding from pasture had the fewest. Being female and being outdoors in winter were associated with increased numbers of inflammatory cells. Older horses had fewer macrophages than young horses. More than 70% of horses had >20% neutrophils in tracheal lavage. Twenty percent of horses had a mucus accumulation score >1; 17% had both a mucus score >1 and >20% neutrophils. The significant risk factors for mucus accumulation >1 were age >15 years, feeding on hay as compared to pasture, and being outdoors for more than 80% time in winter. Even though mucus accumulation score >1 was a risk factor for cough, only half of such horses coughed. Cough and mucus accumulation were associated with increased number of neutrophils.

CONCLUSIONS

In comparison to pasture feeding, hay feeding, particularly from round bales, was associated with an increased number of neutrophils in the airway. Being outdoors in winter was associated with increased numbers of inflammatory cells and with mucus accumulation. Because 70% of horses have >20% neutrophils, this value should not be used as the sole indicator of airway inflammation.

POTENTIAL RELEVANCE

The study reinforces the importance of hay feeding and older age as risk factors for inflammatory airway disease. Horses that do not have 'heaves' may be best kept indoors when winters are cold.

Cytokine expression by peripheral blood neutrophils from heaves-affected horses before and after allergen challenge

Heaves, also known as recurrent airway obstruction, is a common condition of horses characterised by pulmonary neutrophilia and reversible airway obstruction. This study evaluated the role of neutrophils in producing cytokines and chemokines that might be involved in the recruitment and activation of inflammatory cells in horses with heaves. Peripheral neutrophils were isolated from heaves-affected (n = 9) and control (n = 4) horses before and after 5 h of natural inhalation challenge. Expression of mRNA of two pro-inflammatory cytokines, tumour necrosis factor (TNF)-alpha and interleukin (IL)-1beta, along with two chemokines, IL-8 and macrophage inflammatory protein (MIP)-2, was evaluated. After exposure to mouldy hay, horses with heaves had significant airway obstruction and increased numbers of neutrophils in bronchoalveolar lavage samples, compared to control horses. However, there were no differences in the expression of mRNAs of TNF-alpha, IL-1beta, IL-8 and MIP-2 between the two groups, suggesting that the release of cytokines and chemokines by peripheral blood neutrophils is not necessary for the development of heaves.

Endotoxin concentrations within the breathing zone of horses are higher in stables than on pasture

Inflammatory airway disease is common in stabled horses, with a prevalence of 17.3% in Michigan pleasure horses. Stable dust is rich in endotoxin, which may induce neutrophilic airway inflammation. Climatological conditions (ambient temperature and relative humidity) may influence endotoxin concentrations in pastures. The aim of this project was to determine if endotoxin levels in the breathing zone of horses in stables were higher than of horses on pasture, and if the endotoxin on pasture was associated with climatological conditions. Endotoxin exposure of six horses that were stabled or on pasture was determined by a Limulus amebocyte lysate assay. Climatological data were obtained from the US National Climatic Data Center. Endotoxin exposure was significantly higher (about 8-fold) in stables than on pasture. On pasture, endotoxin varied widely, despite constant climatological conditions. It was concluded that stabled horses are exposed to higher endotoxin concentrations than horses on pastures. Local endotoxin concentrations may be more important than ambient climatological conditions in determining endotoxin exposure of individual horses.

Genes and respiratory disease: a first step on a long journey

This review highlights the critical importance of phenotype definition in the understanding of the pathogenesis of respiratory disease in horses. The general approach to genetic studies is discussed and comparative studies of recurrent airway obstruction (RAO) conditions, such as asthma, described in the context of learning more about equivalent equine conditions. The availability of methods to study genetic tests have previously relied on DNA sequence knowledge from man, laboratory and domesticated animals, but recent data from the horse genome sequence are now available. This should facilitate advances in the identification of specific genes for equine diseases. The review summarises the future potential for such studies and places the report in this issue (p 236) by Jost et al. (2007) of the involvement of IL4RA as a candidate gene in RAO into this context.

Obstrução recorrente das vias aéreas em muares: relato de três casos

Relatam-se três casos de obstrução recorrente das vias aéreas em muares com idade média de 10 anos. Os animais eram utilizados para concurso de marcha e criados em campo. Após serem mantidos em cocheiras com cama de serragem e alimentados com feno (tifton e alfafa) e ração comercial, começaram a manifestar intolerância ao exercício e episódios de tosse durante o exercício. Após exames clínico e laboratorial, instituiu-se terapia à base de clenbuterol, dexametazona e bromexina, além de controle ambiental. Após 21 dias de tratamento, ocorreu remissão dos sintomas clínicos. Para comprovação diagnóstica, os animais foram submetidos ao desafio ambiental, por um período de dois dias. Após o tratamento, os três animais voltaram a desempenhar suas atividades atléticas de modo satisfatório.

Prevalence of inflammatory airway disease in national hunt horses referred for investigation of poor athletic performance

REASONS FOR PERFORMING STUDY

Inflammatory airway disease (IAD) is thought to be an important cause of poor performance in young Thoroughbred racehorses. However, little study has been made of IAD in older National Hunt (NH) horses.

OBJECTIVES

To determine the prevalence of IAD in NH racehorses referred for investigation of poor athletic performance and identify some of the risk factors that may be associated with IAD in this group of horses.

METHODS

Tracheal mucus was graded, and tracheal wash (TW) and bronchoalveolar lavage (BAL) performed after treadmill exercise in 91 NH horses referred to the University of Bristol. Comparisons were made between the different methods for diagnosing IAD and potential risk factors investigated.

RESULTS

Tracheal mucus was observed in 68% and lower airway inflammation identified in 70% of horses. There was poor agreement between TW and BAL techniques for a diagnosis of IAD. The prevalence of increased proportions of neutrophils in TW was 40% compared with 59% in BAL. There was a significant association between presence of tracheal mucus and increased neutrophils in TW but not between tracheal mucus and BAL cytology. No significant association between IAD and age, EIPH or URT obstruction was observed.

CONCLUSIONS

Inflammatory airway disease was a common finding in NH horses referred for investigation of poor performance. In contrast to studies in younger, flat racehorses the prevalence of disease did not decrease with increasing age.

POTENTIAL RELEVANCE

Horses of all ages presented for investigation of poor performance require a thorough clinical investigation of the lower airways. The collection of both TW and BAL samples is indicated in order to confirm a diagnosis of IAD.

Comparison of prednisolone and dexamethasone effects in the presence of environmental control in heaves-affected horses

This study was designed to compare the efficacy of oral prednisolone and intramuscular (IM) dexamethasone in heaves-affected horses with environmental control. A total of 16 horses, aged 8-20years, with heaves were included in the study. Complete examinations were performed on Day 0 (before treatment), Day 13 (after treatment) and Day 30. Clinical variables, arterial blood gases, mucus scoring and carina evaluation (during endoscopy), and bronchoalveolar lavage (BAL) cytological analysis were all assessed. The horses were randomly assigned to receive either oral prednisolone (1mg/kg) or IM dexamethasone (0.1mg/kg). The animals were clinically scored and mucus accumulation evaluated. Results were analysed by repeated measures ANOVA with time (days of treatment) and treatment as the main effects. When combined with environmental control, prednisolone and dexamethasone treatments had similar effects on heaves score, blood gases and endoscopic scores. However, dexamethasone had a more beneficial effect on BAL cytology.

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.

Persistent mucus accumulation: a consequence of delayed bronchial mucous cell apoptosis in RAO-affected horses?

This study examined the contribution of delayed apoptosis of bronchial mucous cells to mucus accumulation in equine recurrent airway obstruction (RAO). In pilot studies, Bcl-2, an apoptosis inhibitor, was detected in airway mucous cells of RAO-affected horses in remission and during acute disease, when most mucus was secreted. To study whether delayed apoptosis results in an increase in the number of mucous cells during disease recovery, six RAO-affected and six control horses were fed hay for 5 days to induce inflammation and then pellets for 7 days to partially resolve RAO before euthanasia. RAO-affected horses had more airway obstruction and luminal mucus than control horses under both management systems. At the time of euthanasia, RAO-affected horses had more inflammation and Bcl-2-positive bronchial mucous cells than control animals. In horses with >10 and <10 neutrophils per microliter of bronchoalveolar lavage fluid, >50% and <10% of mucous cells stained positive for Bcl-2, respectively. No differences in mucous cell number or amount of stored mucosubstance were observed between RAO-affected and control horses, but in RAO-affected animals, the amount of stored mucosubstance decreased as the number of neutrophils in bronchoalveolar lavage fluid increased. Because the number of mucous cells was similar in both groups of horses but only mucous cells of RAO-affected horses expressed Bcl-2 during recovery from acute disease, a conclusive role for Bcl-2 in prolonging bronchial mucous cell life could not be determined. Future studies are needed to compare horses that are kept in remission for prolonged periods when all mucous cells are fully developed.