Descriptive results from a longitudinal study of airway inflammation in British National Hunt racehorses

Neutrophil gelatinase-associated lipocalin as a potential biomarker for equine asthma

BACKGROUND

Studies in people have found neutrophil gelatinase-associated lipocalin (NGAL) concentrations are increased in asthma and can be used to distinguish between asthma subtypes. NGAL has not yet been investigated in equine asthma (EA).

OBJECTIVES

To investigate the ability of NGAL concentrations in bronchoalveolar lavage (BAL) fluid and serum to distinguish between control horses, horses with mild-moderate EA (MEA) and horses with severe EA (SEA).

STUDY DESIGN

Retrospective cross-sectional study.

METHODS

Details of endoscopic examination including tracheal mucus score (TMS, scale 0-5) and BAL cytology performed on 227 horses were extracted from records and NGAL concentrations were measured on stored serum and BAL fluid samples. The horses were divided into groups (control group n = 73, MEA n = 98, SEA n = 56) based on clinical signs and BAL cytology results. Differences between groups were evaluated with the Mann-Whitney test and correlation between BAL NGAL, serum NGAL, and BAL cytology were evaluated using Spearman's correlation.

RESULTS

BAL NGAL concentrations were higher in EA than in control horses (median: 25.6 and 13.3 μg/L, respectively, p < 0.001). Concentrations of NGAL in BAL differed between groups, with higher concentrations in MEA than in control horses (median: 18.5 and 13.3 μg/L, respectively, p < 0.001), and higher concentrations in SEA than in MEA horses (median: 54.1 and 18.5 μg/L, respectively, p < 0.001). BAL NGAL concentration differed between horses with TMS ≤2 an >2 (median 15.6 and 21.1 μg/L, respectively, p = 0.004). No differences were found in serum NGAL concentration between any of the groups.

MAIN LIMITATION

Only 66 of the 227 (29%) horses had haematology and serum NGAL measured.

CONCLUSION

BAL NGAL concentration differed between control and EA and reflected severity of disease. These results justify further research into the potential of NGAL as a biomarker of EA.

Associations between postrace atrial fibrillation and measures of performance, racing history and airway disease in horses

BACKGROUND

Atrial fibrillation (AF) is the most common performance limiting arrhythmia in racehorses. High dose exercise and airway disease promote AF in humans. Few studies have investigated epidemiological factors associated with AF in horses.

OBJECTIVES

Explore variables relating to performance, exercise volume and postrace endoscopic findings in horses with AF.

ANIMALS

A total of 164 horses with poor race performance and postrace AF were compared to 321 horses with poor performance without AF (PP) and 314 horses performing to expectation (TE).

METHODS

Horse-level and race-level variables for horses racing in Australia and Hong Kong from 2009 to 2021 were compared using univariable and multivariable logistic regression. Postrace endoscopic exercise-induced pulmonary hemorrhage (EIPH) and tracheal mucus accumulation (TMA) grades for AF and PP horses were compared using chi-squared analysis.

RESULTS

Variables that were significant in the multivariable model of AF compared to TE were distance (lengths) behind the winner, (odds ratio [OR]; 95% confidence interval [95% CI], 1.41 [1.32-1.51], P < .0001), cumulative prize money per start before the event (OR [95% CI] 1.02 [1.01-1.03], P = .01) and age (OR [95% CI] 0.72 [0.55-0.92], P = .01). More AF horses had EIPH grade ≥ 3 (23/109; 21.1%) than PP horses (7/213; 3.3%; OR [95%CI] 7.9 [3.3-20.2], P < .0001).

CONCLUSIONS AND CLINICAL IMPORTANCE

Acute race performance was substantially impaired by AF but career earnings before the event were not inferior. Exercise volume did not promote AF. Higher grades of EIPH found in AF horses suggests a mechanistic relationship between these conditions.

Training associated alterations in equine respiratory immunity using a multiomics comparative approach

Neutrophilic airway inflammation is highly prevalent in racehorses in training, with the term mild to moderate equine asthma (MMEA) being applied to the majority of such cases. Our proposed study is largely derived from the strong association between MMEA in racehorses and their entry into a race training program. The objectives of this study are to characterise the effect of training on the local pulmonary immune system by defining the gene and protein expression of tracheal wash (TW) derived samples from Thoroughbred racehorses prior to and following commencement of race training. Multiomics analysis detected 2138 differentially expressed genes and 260 proteins during the training period. Gene and protein sets were enriched for biological processes related to acute phase response, oxidative stress, haemopoietic processes, as well as to immune response and inflammation. This study demonstrated TW samples to represent a rich source of airway cells, protein and RNA to study airway immunity in the horse and highlighted the benefits of a multiomics methodological approach to studying the dynamics of equine airway immunity. Findings likely reflect the known associations between race-training and both airway inflammation and bleeding, offering further insight into the potential mechanisms which underpin training associated airway inflammation.

Exercise-induced airflow changes in horses with asthma measured by electrical impedance tomography

BACKGROUND

Equine asthma (EA) causes airflow impairment, which increases in severity with exercise. Electrical impedance tomography (EIT) is an imaging technique that can detect airflow changes in standing healthy horses during a histamine provocation test.

OBJECTIVES

To explore EIT-calculated flow variables before and after exercise in healthy horses and horses with mild-to-moderate (MEA) and severe equine asthma (SEA).

ANIMALS

Nine healthy horses 9 horses diagnosed with MEA and 5 with SEA were prospectively included.

METHODS

Recordings were performed before and after 15 minutes of lunging. Absolute values from global and regional peak inspiratory (PIF, positive value) and expiratory (PEF, negative value) flows were calculated. Data were analyzed using a mixed model analysis followed by Bonferroni's multiple comparisons test to evaluate the impact of exercise and diagnosis on flow indices.

RESULTS

Control horses after exercise had significantly lower global PEF and PIF compared to horses with SEA (mean difference [95% confidence interval, CI]: 0.0859 arbitrary units [AU; 0.0339-0.1379], P < .001 and 0.0726 AU [0.0264-0.1188], P = .001, respectively) and horses with MEA (0.0561 AU [0.0129-0.0994], P = .007 and 0.0587 AU [0.0202-0.0973], P = .002, respectively). No other significant differences were detected.

CONCLUSIONS AND CLINICAL IMPORTANCE

Electrical impedance tomography derived PIF and PEF differed significantly between healthy horses and horses with SEA or MEA after exercise, but not before exercise. Differences between MEA and SEA were not observed, but the study population was small.

Training related risk factors for exercise induced pulmonary haemorrhage in British National Hunt racehorses

BACKGROUND

Exercise induced pulmonary haemorrhage (EIPH) is an important condition of horses performing high intensity exercise, with reported prevalence among racehorses of up to 95%, based on the detection of blood on tracheobronchoscopy. Previously identified risk factors include age, sex, season, race type, years spent in racing and lower airway inflammation.

OBJECTIVES

To estimate the prevalence of EIPH in British National Hunt racehorses as indicated by two outcome measures: presence of tracheal blood on tracheobronchoscopy, and presence of moderate-large (significant) proportions of haemosiderophages in tracheal wash (TW) fluid; and to identify training-related risk factors for these indicators of EIPH.

STUDY DESIGN

Prospective longitudinal study.

METHODS

Data from tracheobronchoscopy and TW cytology were analysed using univariable and multivariable mixed-effects logistic regression.

RESULTS

1184 observations, from 177 horses, were analysed. The prevalence of tracheal blood was 7.2% (95%CI: 5.8, 8.8) and significant haemosiderophages in TW fluid was 36% (95%CI: 33.3, 38.8). Increased time in training was significantly associated with increased odds of EIPH. For each additional year spent in training the odds of tracheal blood and presence of significant proportions haemosiderophages increased approximately 1.5-fold (OR = 1.5; 95%CI: 1.1-2.0; P = .005; and OR = 1.5; 95%CI: 1.3, 1.8; P < .001, respectively). Current inflammation was associated with previous haemorrhage, but not current haemorrhage.

MAIN LIMITATIONS

There are no standardised measures for quantification of TW cytological parameters for EIPH diagnosis. Few horses were examined following jumping. Recent racing dates were not included in analysis.

CONCLUSIONS

Increasing time in training was a risk factor for both indicators of EIPH. Current inflammation was associated with previous haemorrhage, but not current or future haemorrhage, suggesting that haemorrhage leads to inflammation but not that inflammation leads to haemorrhage. Overall, our findings are consistent with the capillary stress failure theory of EIPH. The development of standardised measures for TW cytological diagnosis of EIPH is warranted.

The equine mononuclear phagocyte system: The relevance of the horse as a model for understanding human innate immunity

The mononuclear phagocyte system (MPS) is a family of cells of related function that includes bone marrow progenitors, blood monocytes and resident tissue macrophages. Macrophages are effector cells in both innate and acquired immunity. They are a major resident cell population in every organ and their numbers increase in response to proinflammatory stimuli. Their function is highly regulated by a wide range of agonists, including lymphokines, cytokines and products of microorganisms. Macrophage biology has been studied most extensively in mice, yet direct comparisons of rodent and human macrophages have revealed many functional differences. In this review, we provide an overview of the equine MPS, describing the variation in the function and phenotype of macrophages depending on their location and the similarities and differences between the rodent, human and equine immune response. We discuss the use of the horse as a large animal model in which to study macrophage biology and pathological processes shared with humans. Finally, following the recent update to the horse genome, facilitating further comparative analysis of regulated gene expression between the species, we highlight the importance of future transcriptomic macrophage studies in the horse, the findings of which may also be applicable to human as well as veterinary research.

The Relationship between Lung Inflammation and Aerobic Threshold in Standardbred Racehorses with Mild-Moderate Equine Asthma

Simple Summary

Horses can be affected by equine asthma, a disease that shares several similarities with human asthma. Young racehorses can be affected by a mild form of equine asthma, which can have a negative impact on racing performance. In this study, we evaluated the relation between the increase in inflammatory cells in the bronchoalveolar lavage fluid of horses affected by poor performance due to equine asthma and the speed at which the horse blood lactate reaches the value of 4 mmol/L, which is a parameter of athletic capacity. With this aim, we evaluated the results of a treadmill test with blood lactate analysis of 30 horses that had a bronchoalveolar lavage fluid cytology consistent with a mild form of equine asthma. The results showed a significant relation between the increase in the differential count of neutrophils in bronchoalveolar lavage and the decrease in the speed at 4 mmol/L of lactate. This confirm the negative impact of neutrophilic lung inflammation in the presence of equine asthma on athletic capacity and, consequently, on racing performance.

Abstract

Mild–moderate equine asthma (MEA) is a common disease of young racehorses characterized by inflammation of the lower airways diagnosed by cytological examination of bronchoalveolar lavage fluid (BALF), and it is considered an important cause of poor performance. The most common parameter of athletic capacity associated with horse performance is the speed at 4 mmol/L of lactate (VLA4). The aim of the present work was to evaluate the relation between the different BALF inflammatory cells and VLA4 in racehorses affected by MEA. A population of Standardbred racehorses that underwent an accurate protocol for poor performance evaluation was collected for a retrospective study. Horses with any other alteration potentially influencing performance were excluded, thus considering only subjects with BALF cytology consistent with MEA. A sample of 30 horses (3.4 ± 1.0 years old) was selected. The relationship between BALF inflammatory cell differential count and VLA4 was evaluated by means of linear regression. Statistical analysis showed a significant relation (p = 0.015, r² = 0.19) between the increase in the differential count of neutrophils in BALF and the decrease in VLA4. The results obtained suggested that the accumulation of neutrophils in the airways of MEA horses may have a direct impact on athletic capacity, possibly due to impaired alveolar blood-gas exchanges during strenuous exercise.

Conflict Between Direct Experience and Research-Based Evidence Is a Key Challenge to Evidence-Based Respiratory Medicine on British Racing Yards

Inflammatory airway disease (IAD) is a commonly diagnosed but variably defined syndrome of equine lower airway inflammation. The most recent American College of Veterinary Internal Medicine (ACVIM) consensus statement, informed by research evidence, recommends a case definition based on clinical signs (poor performance or occasional coughing of at least 3 weeks duration), increased endoscopically-visible tracheal mucus, and bronchoalveolar lavage cytology, and proposes that the condition should be termed ‘mild-moderate equine asthma' (mEA). In British Thoroughbred racehorses, research to date has focused on airway inflammation defined by increased tracheal mucus and inflammatory tracheal wash sample cytology. It has been unclear whether or to what extent the ACVIM consensus statement has influenced the practice of British racing veterinarians. The aim of this qualitative study was to characterize and understand rationales for current practices relating to diagnosing and managing airway inflammation in British racehorses. Audio-recorded focus group discussions were conducted with 25 participants from four veterinary practices in England. Practices were purposively selected to represent those responsible for different types of racehorse, in different geographical regions. Thematic analysis of transcripts identified (i) an over-arching theme of serving the racing industry within which two further themes (ii) disregarding of the consensus and (iii) the pragmatic clinician were nested. The requirement to serve the racing industry was a key driver of clinical approaches, strongly influenced in particular by the trainer. Participants widely disregarded the consensus case definition of IAD/mEA for British racehorses because of perceived differences in etiology, perceived lack of practicability, particularly of BAL sampling, and perceived lack of understanding of the British racing context by consensus authors. Participants shared a strong professional identity as pragmatic clinicians providing an individualized clinical approach based on direct experience, which was often prioritized as the most valuable evidence with which to inform clinical decision-making. Lack of alignment with international consensus presents a barrier to practicing and furthering evidence-based medicine. Improved dialogue and partnership in research would be valuable and further research tailored for this population, including continuing development of contextually acceptable diagnostic methods, may be required.

Equine asthma: Integrative biologic relevance of a recently proposed nomenclature

The term “equine asthma” has been proposed as a unifying descriptor of inflammatory airway disease (IAD), recurrent airway obstruction (RAO), and summer pasture‐associated obstructive airway disease. Whilst the term will increase comprehensibility for both the lay and scientific communities, its biologic relevance must be compared and contrasted to asthma in human medicine, recognizing the limited availability of peer‐reviewed equine‐derived data, which are largely restricted to clinical signs, measures of airway obstruction and inflammation and response to therapy. Such limitations constrain meaningful comparisons with human asthma phenotypes. Suggested minimum inclusion criteria supporting the term asthma, as well as similarities and differences between IAD, RAO, and multiple human asthma phenotypes are discussed. Furthermore, differences between phenotype and severity are described, and typical features for equine asthma subcategories are proposed. Based on shared features, we conclude that mild/moderate (IAD) and severe (RAO) equine asthma are biologically appropriate models for both allergic and non‐allergic human asthma, with RAO (severe equine asthma) also being an appropriate model for late‐onset asthma. With the development of new biologic treatments in humans and the application of more targeted therapeutic approaches in the horse, it would appear appropriate to further investigate the allergic (Th‐2) and non‐allergic (non‐Th‐2) phenotypes of equine asthma. Further research is required to more fully determine the potential clinical utility of phenotype classification.

Exhaled breath condensate hydrogen peroxide, pH and leukotriene B4 are associated with lower airway inflammation and airway cytology in the horse

BACKGROUND

Exhaled breath condensate (EBC) analysis is a noninvasive method to assess the lower respiratory tract. In human subjects, EBC hydrogen peroxide (H₂ O₂ ), pH and leukotriene B₄ (LTB₄ ) are useful for detection and monitoring of inflammatory lung diseases, including asthma.

OBJECTIVES

To determine associations between EBC biomarkers and cytological and endoscopic definitions of lower airway inflammation (LAI) while controlling for sampling and environmental variables.

STUDY DESIGN

Prospective, cross-sectional study.

METHODS

Clinical, endoscopic and airway cytological findings from 47 horses were compared with EBC pH and concentrations of H₂ O₂ and LTB₄ by univariate and multivariable analyses. Dichotomous (presence/absence of airway inflammation) and continuous outcome variables (differential cell counts in tracheal aspirate and bronchoalveolar lavage fluid, BALF) were evaluated and potential effects of collection and methodological factors were included.

RESULTS

EBC pH and H₂ O₂ concentrations were higher in horses with LAI and both were positively associated with the percentage of neutrophils in BALF (P<0.05). Mast cell percentage in BALF was negatively associated with EBC pH, and BALF eosinophil percentage was positively associated with EBC LTB₄ (P<0.05). Ambient temperature, relative humidity and assay methodology significantly impacted some analytes.

MAIN LIMITATIONS

LAI is challenging to categorise due to a variety of clinical and cytological phenotypes. Although the study was designed to overcome this limitation, numbers of horses were small in some categories.

CONCLUSIONS

EBC pH and H₂ O₂ concentrations are altered by airway inflammation, suggesting a role for these biomarkers in the diagnosis and monitoring of airway disease. Environmental and methodological factors can influence these biomarkers and should be considered in the interpretation of results.

Association of neutrophil morphology with bacterial isolates in equine tracheal wash samples

BACKGROUND

Tracheal wash sample neutrophilia is common in lower airway inflammation of various causes; however, relevance of cytomorphological features to culture of bacterial pathogens has not been established.

OBJECTIVES

To investigate whether the presence of nondegenerate or degenerate neutrophils in tracheal washes is associated with culture of bacteria and, if so, whether this is influenced by age or temporal factors.

STUDY DESIGN

Cross-sectional study.

METHODS

Tracheal wash samples submitted to Rossdales LLP from 1/1/2013 to 31/7/2015 were evaluated using set criteria. Neutrophilia and degenerate neutrophilia (graded ≥2/4 on Rossdales cytological scale [0-4]) were analysed in relation to bacterial isolates considered potentially pathogenic in respiratory disease. Statistical analyses included multivariable logistic regression to identify associations between two separate outcomes: 1) the presence of neutrophilia compared with no neutrophilia and 2) the presence of degenerate neutrophilia compared with nondegenerate neutrophilia and four independent variables.

RESULTS

Sufficient data for inclusion in the multivariable model for nondegenerate neutrophilia were available from 1100 horses. Culture of potentially pathogenic bacteria was associated with increased odds of degenerate neutrophilia compared with samples with negative culture (OR 4.5, 95% CI 3.1, 6.4, P-value<0.001). Horses over 9 years old had lower odds of having degenerate neutrophilia than those aged 1-3 years (OR 0.6, 95% CI 0.4, 0.9, P-value<0.02). In the spring/summer, horses had reduced odds of a degenerate neutrophilia compared with winter (OR 0.4, 95% CI 0.3, 0.7, P-value <0.001).

MAIN LIMITATIONS

The study relied on routine laboratory submissions, with no control over sample collection or submitted clinical history.

CONCLUSIONS

Cytological evaluation of tracheal washes should include cytomorphological features of the neutrophil response. The presence of degenerate neutrophils, especially in young horses, indicates added value of culture and sensitivity for antimicrobial therapeutics. The absence of degenerate changes, in combination with clinical factors, can help support diagnosis of a nonseptic cause of airway neutrophilia.

Association of tracheal mucus or blood and airway neutrophilia with racing performance in Thoroughbred horses in an Australian racing yard

OBJECTIVES

To determine the variation of tracheal mucus scores, tracheal blood scores and transendoscopic tracheal wash (TW) cytology in a population of Thoroughbred (TB) racehorses and assess their association with racing performance.

METHODS

A total of 220 endoscopic examinations were performed and TWs obtained from 155 TB racehorses. Samples were collected 60-120 min following gallop work. Tracheal mucus score, tracheal blood score and TW cytology were analysed and their association with racing performance assessed.

RESULTS

Of the total examinations and samples, 194 from 135 horses fitted the criteria for inclusion. The overall prevalence of visible tracheal mucus was 2.5% (5/194) and of increased tracheal mucus was 0%. The prevalence of visible tracheal blood was 8.8% (17/194) and of increased tracheal blood was 4.6% (9/194). A total of 36% (70/194) of TWs contained elevated percentages of neutrophils and of these, 96% (67/70) occurred in the absence of any visible tracheal mucus. There was no significant association between tracheal mucus score or TW cytology and subsequent racing performance. There was a statistically significant association (P = 0.004) between increased tracheal blood scores and poor racing performance.

CONCLUSIONS

Visible tracheal blood seen after strenuous exercise in clinically normal TB racehorses was a risk factor for poor racing performance, but the presence of airway neutrophilia was not. No horses in this study were found to have increased tracheal mucus, so the association of increased tracheal mucus with racing performance could not be assessed.

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.

The innate immune response of equine bronchial epithelial cells is altered by training

Respiratory diseases, including inflammatory airway disease (IAD), viral and bacterial infections, are common problems in exercising horses. The airway epithelium constitutes a major physical barrier against airborne infections and plays an essential role in the lung innate immune response mainly through toll-like receptor (TLR) activation. The aim of this study was to develop a model for the culture of equine bronchial epithelial cells (EBEC) in vitro and to explore EBEC innate immune responses in trained horses. Bronchial epithelial biopsies were taken from 6 adult horses during lower airway endoscopy. EBEC were grown in vitro by an explant method. The innate immune response of EBEC was evaluated in vitro by treatment with TLR ligands. TLR3 is the most strongly expressed TLR at the mRNA level in EBEC and stimulation of EBEC with Poly(I:C), an analog of viral dsRNA, triggers a strong secretion of IFN-β, TNF-α, IL-6 and CXCL8. We further evaluated the EBEC innate immune response in horses that underwent a 4-month-training program. While training had no effect on TLR mRNA expression in EBEC as well as in bronchial biopsies, it increased the production of IFN-β after stimulation with a TLR3 ligand and decreased the secretion of TNF-α and IL-6 after stimulation with a TLR2 and TLR3 ligand. These findings may be implicated in the increased risk for viral and bacterial infections observed in sport horses. Altogether, we report a successful model for the culture of EBEC that can be applied to the investigation of pathophysiologic conditions in longitudinal studies.

Airborne particulates (PM10) and tracheal mucus: A case-control study at an American Thoroughbred racetrack

REASONS FOR PERFORMING STUDY

Particle mapping within stalls has demonstrated a relationship between particulate concentrations and visible accumulations of tracheal mucus. However, measurement of breathing zone particulate concentrations, which is the most accurate way to measure exposure, has not been performed to determine the relationship between exposures and accumulations of tracheal mucus sufficient to affect performance.

OBJECTIVES

To compare breathing zone particulate exposures between horses with tracheal mucus scores (MS) previously demonstrated to affect performance (MS≥2) and those without (MS = 0) visible tracheal mucus.

STUDY DESIGN

Case-control study.

METHODS

We endoscopically examined 649 Thoroughbred racehorses over 7 months and selected 113 age-matched cases and controls based on the presence (MS≥2) or absence (MS = 0) of tracheal mucus, respectively. Inflammatory cell numbers in tracheal lavage were also determined. Breathing zone monitors recorded particulate exposure during 3 time periods (mid-day, evening and overnight). Total recording time averaged 17.5 h/horse.

RESULTS

The overall prevalence of MS≥2 in the observed stables was 23%. Breathing zone particular matter (PM10) concentrations were very similar to previously reported ambient concentrations. During the evening and overnight, cases had significantly higher breathing zone PM10 concentrations and neutrophil counts than controls. Inflammatory cell counts were associated with average PM10 concentrations throughout the day.

CONCLUSIONS

Breathing zone particulate concentrations are associated with MS≥2 and inflammatory cell numbers. If breathing zone particulate exposures are predominantly influenced by ambient PM concentrations, racing stable management practices to reduce particle exposures should greatly reduce the prevalence of tracheal mucus.

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.

Muc5b is the major polymeric mucin in mucus from thoroughbred horses with and without airway mucus accumulation

Mucus accumulation is a feature of inflammatory airway disease in the horse and has been associated with reduced performance in racehorses. In this study, we have analysed the two major airways gel-forming mucins Muc5b and Muc5ac in respect of their site of synthesis, their biochemical properties, and their amounts in mucus from healthy horses and from horses with signs of airway mucus accumulation. Polyclonal antisera directed against equine Muc5b and Muc5ac were raised and characterised. Immunohistochemical staining of normal equine trachea showed that Muc5ac and Muc5b are produced by cells in the submucosal glands, as well as surface epithelial goblet cells. Western blotting after agarose gel electrophoresis of airway mucus from healthy horses, and horses with mucus accumulation, was used to determine the amounts of these two mucins in tracheal wash samples. The results showed that in healthy horses Muc5b was the predominant mucin with small amounts of Muc5ac. The amounts of Muc5b and Muc5ac were both dramatically increased in samples collected from horses with high mucus scores as determined visually at the time of endoscopy and that this increase also correlated with increase number of bacteria present in the sample. The change in amount of Muc5b and Muc5ac indicates that Muc5b remains the most abundant mucin in mucus. In summary, we have developed mucin specific polyclonal antibodies, which have allowed us to show that there is a significant increase in Muc5b and Muc5ac in mucus accumulated in equine airways and these increases correlated with the numbers of bacteria.