Respirable dust concentrations in equine stables. Part 2: The benefits of soaking hay and optimising the environment in a neighbouring stable

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.

Towards personalized medicine for the treatment of equine asthma

Although horses with asthma share similar clinical signs, the heterogeneity of the disease in terms of severity, triggering factors, inflammatory profile, and pathological features has hindered our ability to define biologically distinct subgroups. The recognition of phenotypes and endotypes could enable the development of precision medicine, including personalized, targeted therapy, to benefit affected horses. While in its infancy in horses, this review outlines the phenotypes of equine asthma and discusses how knowledge gained from targeted therapy in human medicine can be applied to evaluate the potential opportunities for personalized medicine in equine asthma and to suggest avenues for research to advance this emerging field.

Environmental Management of Equine Asthma

Environmental practices related to the inhalation of airborne dust have been identified as the main cause of equine asthma (EA) and reasonably, they are truly relevant in its treatment and control, especially for horses with its severe form. Vast research regarding environmental recommendations has been conducted in recent years. However, no recent exhaustive reviews exist that gather all this new evidence. The aim of this review is to report and compare the most pertinent information concerning the environmental management of EA. The main findings highlight the importance of the type of forage used for feeding but also its method of production and possible contamination during manufacture and/or storage. Procedures to reduce this, such as soaking and steaming hay, improve its hygienic quality, although they also decrease forage's nutritional value, making dietetic supplementation necessary. Regarding stabling, despite some conflicting results, avoiding straw as bedding and improving barn ventilation continue to be the common recommendations if turning to pasture is not feasible. Finally, owners' compliance has been identified as the most critical point in correct environmental control. Educating owners about the genuine benefits of these measures should be a cornerstone of EA management.

Effects of soaked hay on lung function and airway inflammation in horses with severe asthma

BACKGROUND

Reducing inhaled dust particles improves lung function in horses with severe asthma. Soaked hay is commonly used by owners, but its efficacy in improving lung function and inflammation has not been documented.

OBJECTIVES

To measure the effects of soaked hay and alfalfa pellets in horses with severe asthma.

ANIMALS

Ten adult horses with severe asthma from a research colony.

METHODS

Prospective controlled trial. Horses in clinical exacerbation were housed indoors and allocated to be fed either soaked hay (n = 5) or alfalfa pellets (n = 5) for 6 weeks. Soaked hay was immersed for 45 minutes and dried out hay was discarded between meals. Pulmonary function and clinical scores were measured before and after 2, 4, and 6 weeks. Tracheal mucus scores and bronchoalveolar lavages were performed before and after 6 weeks. Lung function was analyzed with a linear mixed model using log-transformed data.

RESULTS

Lung resistance decreased from (median (range)) 2.47 (1.54-3.95) to 1.59 (0.52-2.10) cmH2 O/L/s in the pellets group and from 1.89 (1.2-3.54) to 0.61 (0.42-2.08) cmH2 O/L/s in the soaked hay group over the 6-week period for an average difference of 1.06 cmH2 O/L/s for pellets (95% confidence interval [95% CI]: 0.09-2.04, P = .03, not significant after correction) and 1.31 cmH2 O/L/s for soaked hay (95% CI: -0.23 to 2.85, P < .001, significant).

CONCLUSION AND CLINICAL IMPORTANCE

Soaked hay can control airway obstruction in horses with severe asthma. The strict protocol for soaking and discarding dried-out hay in this study could however be considered too great of an inconvenience by owners.

Effects of low-dust forages on dust exposure, airway cytology, and plasma omega-3 concentrations in Thoroughbred racehorses: A randomized clinical trial

BACKGROUND

Racehorses commonly develop evidence of mild asthma in response to dust exposure. Diets deficient in omega-3 polyunsaturated fatty acids (Ω-3) might exacerbate this response.

HYPOTHESIS

To compare dust exposure, bronchoalveolar lavage fluid (BALF) cytology, and plasma Ω-3 and specialized pro-resolving mediators (SPM) concentrations amongst racehorses fed dry hay, steamed hay, and haylage.

ANIMALS

Forty-three Thoroughbred racehorses.

METHODS

Prospective clinical trial. Horses were randomly assigned to be fed dry hay, steamed hay, or haylage for 6 weeks. Measures of exposure to dust in the breathing zone were obtained twice. At baseline, week-3, and week-6, BALF cytology was examined. Plasma lipid profiles and plasma SPM concentrations were examined at baseline and week 6. Generalized linear mixed models examined the effect of forage upon dust exposure, BALF cytology, Ω-3, and SPM concentrations.

RESULTS

Respirable dust was significantly higher for horses fed hay (least-square mean ± s.e.m. 0.081 ± 0.007 mg/m³ ) when compared with steamed hay (0.056 ± 0.005 mg/m³ , P = .01) or haylage (0.053 ± 0.005 mg/m³ , P < .01). At week 6, BALF neutrophil proportions in horses eating haylage (3.0% ± 0.6%) were significantly lower compared with baseline (5.1 ± 0.7, P = .04) and horses eating hay (6.3% ± 0.8%, P < .01). Plasma eicosapentaenoic acid to arachidonic acid ratios were higher in horses eating haylage for 6 weeks (0.51 ± 0.07) when compared with baseline (0.34 ± 0.05, P < .01) and horses eating steamed (0.24 ± 0.02, P < .01) or dry hay (0.25 ± 0.03, P < .01).

CONCLUSIONS AND CLINICAL IMPORTANCE

Steamed hay and haylage reduce dust exposure compared with dry hay, but only haylage increased the ratio of anti-inflammatory to pro-inflammatory lipids while reducing BAL neutrophil proportions within 6 weeks.

Effects of Bedding Material on Equine Lower Airway Inflammation: A Comparison of Two Peat Beddings, Wood Pellet, and Straw Pellet

The effects of bedding material on air quality are important amongst horses worldwide. Respiratory diseases, especially equine asthma, are highly prevalent with air hygiene playing a major role on the pathophysiology of these diseases. The objective of our study was to investigate the effects of four bedding materials on the respiratory signs, tracheal mucus score, and tracheal wash (TW) and bronchoalveolar lavage fluid (BALF) cytology in healthy adult horses. The study design was a prospective controlled cross-over study, and the subjects were healthy adult riding school horses (n = 32) from a single stable. Wood pellet, straw pellet, and loosely stored peat (Peat 3) were compared to peat packed in plastic-covered bales (Peat 2). Lower airway endoscopy and sampling (TW and BALF) for cytological examination were performed after each 35-day bedding period. The tracheal mucus scores (P = 0.014) and respiratory rate (P = 0.026) were higher during the straw pellet period compared to the Peat 2 period. The respiratory rate was lower during the wood pellet period compared to the Peat 2 period (P = 0.004). The TW neutrophil percentage during the straw pellet period was higher compared to the Peat 2 period (P = 0.0003). The BALF neutrophil percentage was higher during the straw pellet period (P = 0.005) and during the Peat 3 period compared to the Peat 2 period (P = 0.04). We conclude that baled peat (Peat 2) caused lower neutrophil percentages in the airway samples compared to straw pellet and loosely stored peat (Peat 3). No difference was observed between Peat 2 and wood pellet. The information gained from this study may assist veterinarians and horse owners in selecting appropriate bedding materials, especially for horses with equine asthma.

Feed Intake Parameters of Horses Fed Soaked or Steamed Hay and Hygienic Quality of Hay Stored following Treatment

Simple Summary

Dusty hay is particularly harmful to horses with equine asthma, where the dust mainly consists of microbial deposits in addition to abiotic ones. Soaking and steaming hay can improve its hygienic quality by rinsing off dust, but also reducing the viability of microorganisms. In this study, we investigated whether the treated hay remains stable during subsequent storage, and how the horses’ feed intake as well as chewing activity change with treated hay. Microbial counts were determined by culture methods in meadow hay before and after soaking or steaming, and subsequent storage at 10 and 25 °C for 6, 12 and 24 h. Chewing activity was monitored while horses consumed native or treated hay. Steaming effectively reduced yeasts and typical mold. Steamed hay was almost stable during storage, but storing soaked hay increased yeasts, and typical bacteria and mold. The intake of soaked hay was characterized by a particularly low consumption rate and high chewing intensity, but these per se positive effects seemed to be biased by a lower acceptance. However, steaming can be used to reduce counts of viable microorganisms. The feeding of soaked hay is recommended directly after treatment, to avoid hygienic problems.

Abstract

Horses suffering from equine asthma must consume low-dust forage, with soaking and steaming being suitable methods of hay treatment. The impacts of this treated hay’s subsequent storage and effects on the horses’ chewing activity are largely unknown. Meadow hay was soaked (10–15 °C, 15 min) or steamed (100 °C, 60 min). Microbial counts (colony forming units (CFU)) were determined by culture before and after soaking or steaming, and subsequent storage at 10 and 25 °C for 6, 12 and 24 h (three replicates each). Six horses were fed native, soaked and steamed hay, according to a cross-over design, and chewing parameters were measured. Steaming reduced (p < 0.05) typical mold vs. soaking (0 vs. 50 CFU/g) and yeasts vs. native and steamed hay (0 vs. 102 and 90 CFU/g). Storing soaked hay elevated bacteria, mold, and yeasts (p < 0.05). Within the first 60 min of hay intake, the steamed hay and soaked hay were eaten slower (19.5 and 21.5 g dry matter/min, respectively; p < 0.05) and the steamed hay was chewed more intensely (steamed hay: 3537; native: 2622; and soaked: 2521 chewing cycles/kg dry matter, p < 0.05). Steaming particularly improves the hygienic quality of hay. Soaked hay is not stable when stored and is less accepted by horses.

Effects of Bedding Material on Equine Lower Airway Inflammation: A Crossover Study Comparing Peat and Wood Shavings

Bedding materials affect stable air hygiene, and thus the development and exacerbation of equine asthma. There is limited knowledge concerning the effects of different types of bedding material on equine lower airway inflammation. The objective of our study was to investigate the effects of bedding materials on respiratory signs, tracheal mucus score, and lower airway cytology in healthy adult horses. The study design was a prospective controlled study, and the subjects were healthy adult riding school horses (n = 32) from a single stable. Wood shavings were compared to peat, which was used as a reference bedding material. Lower airway endoscopy and sampling (tracheal wash and bronchoalveolar lavage fluid) for cytological examination were performed after each 35-day bedding period. No difference between bedding periods was observed in the respiratory rate or tracheal mucus score. Tracheal wash neutrophil percentage with the wood shavings was higher compared to the previous (P = 0.040) or following (P = 0.0045) peat period. Bronchoalveolar lavage fluid neutrophil percentage with the wood shavings was higher compared to the following peat period (P < 0.001). We conclude that, between the two bedding materials used in this study, peat caused less neutrophilic lower airway inflammation in horses. The information gained from this study may assist veterinarians and horse owners in selecting bedding materials, especially for horses suffering from equine asthma.

Effect of Hay Soaking Duration on Metabolizable Energy, Total and Prececal Digestible Crude Protein and Amino Acids, Non-Starch Carbohydrates, Macronutrients and Trace Elements

Soaking hay before feeding has been documented to reduce airborn respirable particles and water-soluble carbohydrate (WSC) content which may have positive benefits for horses suffering from Equine Asthma (EA) or Equine Metabolic Syndrome (EMS). Prolonged soaking also leaches minerals, but to-date no measurement of the loss of small intestine digestible crude protein has been documented. One aim of this study was to investigate various soaking durations on nutrient contents of hay, WSC, macronutrients, and trace elements levels. Another objective was to determine the prececal digestible crude protein (pcd CP) and amino acid (pcd AA) fraction contents and prececal digestibility (pcD). Four different batches of meadow hay were soaked in water (20° C during preparation) for 0 minutes, 15 minutes, 30 minutes, 60 minutes, and 12 hours and drained for 20 minutes. A 15 minutes soaking duration significantly reduced the levels of nearly all investigated nutrients (e.g. for fructans, and WSC, macronutrients and trace elements). However, the crude fiber, acid detergent fiber (ADF), and acid detergent lignin content increased. Metabolizable energy (ME) contents decreased by 5-15 %, pcd CP and pcd AA fell by 35 %, and the pcD declined by up to 49 %. In contrast, the pcD was 56 % before soaking. Longer soaking durations did not enhance the wash-out effect. Horse owners should be aware that soaking hay, regardless of reason, may negatively alter the nutritional value. The wide range of wash-out effects may pose risks in calculating the correct dry matter portion to prevent weight loss and maintain ME, pcd CP and pcd AA requirements, especially for horses with EMS and EA.

Owner Compliance to an Environmental Management Protocol for Severe Equine Asthma Syndrome

Severe equine asthma (SEA) syndrome is a chronic recurrent respiratory disease, common among adult horses. The disease occurs in genetically susceptible individuals after their exposure to organic dust. Thus, environmental management has proved essential in controlling airway challenge and disease exacerbation. This is a demanding process that can only be achieved through the horse owners' cooperation. One year after initial diagnosis of SEA in a group of 39 horses, owner compliance to an environmental management protocol was evaluated. The overall compliance to the protocol was poor and the horses' clinical health and need for pharmacological management was related to the successful implementation of the environmental recommendations provided on disease diagnosis.

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.

Comparative Review of Asthma in Farmers and Horses

PURPOSE OF REVIEW

Farmers are routinely exposed to organic dusts and aeroallergens that can have adverse respiratory health effects including asthma. Horses are farm-reared large animals with similar exposures and can develop equine asthma syndrome (EAS). This review aims to compare the etiology, pathophysiology, and immunology of asthma in horses compared to farmers and highlights the horse as a potential translational animal model for organic dust-induced asthma in humans.

RECENT FINDINGS

Severe EAS shares many clinical and pathological features with various phenotypes of human asthma including allergic, non-allergic, late onset, and severe asthma. EAS disease features include variable airflow obstruction, cough, airway hyperresponsiveness, airway inflammation/remodeling, neutrophilic infiltrates, excess mucus production, and chronic innate immune activation. Severe EAS is a naturally occurring and biologically relevant, translational animal disease model that could contribute to a more thorough understanding of the environmental and immunologic factors contributing to organic dust-induced asthma in humans.

The influence of hay steaming on clinical signs and airway immune response in severe asthmatic horses

Background

Avoidance of antigenic stimuli was found to significantly reverse airway obstruction of horses with severe equine asthma (sEA). To date, no published study investigated the influence of steaming hay on lower airway condition of sEA-affected horses. The objectives were to determine the clinical, cytological and cytokine respiratory responses of both sEA and control (CTL) horses experimentally exposed to steamed or dry hay.

Results

A cohort of 6 sEA horses and 6 CTL horses was involved in this field study. On day 0, both groups were fed with steamed hay for 5 consecutive days, followed by a wash-out period of 26 days prior to be fed with dry hay for 5 consecutive days. Investigations performed 2 days prior to and 5 days after each challenge included clinical score, tracheal mucus accumulation, and bronchoalveolar lavage fluid (BALF) cytology and cytokine mRNA expression. Feeding steamed hay significantly decreased its mould content (P < 0.001). Mucus score significantly increased when feeding dry hay (P = 0.01). No significant influence of challenge type was found on clinical score. Percentages of neutrophils (P < 0.001) as well as mRNA expression of IL-1β (P = 0.024), IL-6R (P = 0.021), IL-18 (P = 0.009) and IL-23 (P = 0.036) in BALF of sEA affected horses were significantly increased after both (steamed and dry hay) challenges. Relative mRNA expression of IL-1β, IL-6R and IL-23 in BALF were also significantly correlated to neutrophil percentages and both clinical and tracheal mucus score.

Conclusions

Steaming significantly decreased mould content but inconsistently influenced the respiratory response of sEA affected horses when fed hay. Based on BALF cytology and cytokine profiles, its relevance might be controversial as a non-medicinal therapy for sEA-affected horses.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1636-4) contains supplementary material, which is available to authorized users.

Effect of ionization, bedding, and feeding on air quality in a horse stable

BACKGROUND

Organic dust is associated with Equine asthma. Ionization should reduce airborne dust levels.

OBJECTIVES

To determine the effect of ionization of air, type of bedding, and feed on the levels of airborne dust, endotoxin, and fungal colonies in horse stables.

ANIMALS

24 healthy University-owned horses occupied the stables.

METHODS

A randomized controlled cross-over study. Four units with 6 stables were equipped with an ionization installation (25 VA, 5000 Volt Direct Current). Horses were kept either on wood shavings and fed haylage (2 units), or on straw and fed dry hay (2 units). Measurements were performed with and without activated ionization, during daytime and nighttime, repeatedly over the course of a week and repeatedly during 4-6 weeks. Statistical analysis was performed using a mixed effect model with Akaike's Information Criterion for model reduction and 95% profile (log) likelihood confidence intervals (CI).

RESULTS

Ionization did not alter concentrations of dust, endotoxin, or fungi, fewer. In the units with straw and hay, the concentration of dust, endotoxin, and fungi (difference in logarithmic mean 1.92 (95%CI 1.71-2.12); 2.86 (95%CI 2.59-3.14); 1.75 (95%CI 1.13-2.36)) were significantly higher compared to wood shavings and haylage.

CONCLUSIONS AND CLINICAL IMPORTANCE

The installation of a negative air-ionizer in the horse stable did not reduce concentrations of dust, endotoxin, and viable fungal spores. The substantial effect of low dust bedding and feed is confirmed.

The effect of stable bedding materials on dust levels, microbial air contamination and equine respiratory health

The choice of bedding material affects the quality of air in a stable and, consequently, the respiratory health of horses and humans. The risk of respiratory problems can be mitigated by improving the quality of air in the stable. The choice of bedding material is particularly important in cold climate conditions where horses are kept indoors throughout the year. This study examined the impact of three bedding materials: straw (S), peat with shavings (PS), and crushed wood pellets (CWP). The investigated factors were air contamination, including dust contamination and microbial (bacterial and fungal) contamination, and the condition of the equine respiratory tract. The condition of the respiratory tract was evaluated based on the results of arterial blood biochemistry tests and endoscopic evaluations of the upper respiratory tract. Mechanical dust contamination was lowest for PS (1.09mg/m³) and highest for CWP (4.07mg/m³). Bacterial contamination (in CFU - colony forming units) was highest for PS (5.14log₁₀CFU/m³) and lowest for CWP (4.81log₁₀CFU/m³). Fungal air contamination was lowest for CWP (4.54log₁₀CFU/m³) and highest for S (4.82log₁₀CFU/m³) and PS (4.88log₁₀CFU/m³). An analysis of physiological indicators revealed that all horses were clinically healthy regardless of the type of applied bedding. The type of bedding material did not exert a clear influence on arterial blood biochemistry or the results of endoscopic evaluations of the respiratory tract; however, the use of alternative for straw bedding materials improved endoscopy results.

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.

Reducing Respiratory Health Risks to Horses and Workers: A Comparison of Two Stall Bedding Materials

Simple Summary

In this study, the effect of wood shavings and peat was examined on stable air quality and health of horses and stable workers. The ammonia level in the boxes in which peat was used as bedding was non-existent or very low. The respiratory symptoms in horses increased regardless of the bedding material at the beginning of the study. The health status of the horses on peat bedding returned to the initial level in the end of the trial but horses in stalls bedded with wood shavings continued to be symptomatic. The hooves of the horses in stalls with peat bedding had a better moisture content. The results suggest that peat is a better bedding material for horses and people working or visiting horse stables than wood shavings.

Abstract

Stable air quality and the choice of bedding material are an important health issue both in horses and people working or visiting horse stables. Risks of impaired respiratory health are those that can especially be avoided by improving air quality in the stable. The choice of bedding material is particularly important in cold climate conditions; where horses are kept most of the day and year indoors throughout their life. This study examined the effect of two bedding materials; wood shavings and peat; on stable air quality and health of horses. Ammonia and dust levels were also measured to assess conditions in the stable. Ammonia was not detected or was at very low levels (<0.25 ppm) in the boxes in which peat was used as bedding; but its concentration was clearly higher (1.5–7.0 ppm) in stalls with wood shavings as bedding. Personal measurements of workers revealed quite high ammonia exposure (5.9 ppm_8h) in the boxes in which wood shavings were used; but no exposure was observed in stalls bedded with peat. The respiratory symptoms in horses increased regardless of the bedding material at the beginning of the study. The health status of the horses in the peat bedding group returned to the initial level in the end of the trial but horses bedded with wood shavings continued to be symptomatic. The hooves of the horses with peat bedding had a better moisture content than those of the horses bedded with wood shavings. The results suggest that peat is a better bedding material for horses than wood shavings regarding the health of both horses and stable workers.

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.

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.

Variability in particulate concentrations in a horse training barn over time

REASONS FOR PERFORMING STUDY

Exposure of horses to airborne particulates during stable confinement has been linked with airway inflammation in these animals. Understanding that link requires accurate measures of exposures and greater understanding of the sources of variability in these exposures.

OBJECTIVES

Area and breathing zone particulate concentrations were measured over time in order to determine the relative variability introduced by daily, monthly or between horse variations. Additionally, the relationship between area and breathing zone respirable particulate concentrations was examined.

METHODS

The study was conducted in a Thoroughbred training stable. Breathing zone and area respirable particulate concentrations were measured over a 30-month period. Mixed-model analysis of variance was used to determine effect of month and year at the time of sampling and the daily variance upon area particulate concentrations. The effects of hay feeding method and horse variance on breathing zone measures were included in the model. Real-time concentrations of particulate matter with an aerodynamic diameter of 10 microm or smaller (PM10) were measured to determine the effect of barn door position. Significance was set at P < 0.05.

RESULTS

Average area particulate concentration varied with month and year of sampling but daily variation was not significant. Maximum area respirable particulate concentrations were significantly affected by daily variation. Opening barn doors resulted in lower PM10 levels. Horses fed from hay nets were exposed to significantly higher concentrations of respirable particulates in their breathing zone than when fed hay on the ground. Horse-to-horse variability was significant. Breathing zone concentrations were significantly greater than area concentrations and the 2 measurements were not correlated.

CONCLUSIONS

While area respirable particulate concentrations reflected seasonal changes, these measures are poor predictors of individual horse exposure. Instead, methods of feeding and individual horse behaviour are important determinants of exposure.

POTENTIAL RELEVANCE

Studies investigating the effect of natural exposures on lung health in horses should consider the effects of individual behaviour and management practices on breathing zone exposure.

How to improve the hygienic quality of forages for horse feeding

BACKGROUND

Improving the hygienic quality of forages for horse nutrition seems to be a reasonable target for decreasing the prevalence of pulmonary diseases. The aim of the experiment was to study the effects of different agricultural practices on the main aero-allergens contained in forages, including breathable dust, fungi, mycotoxins and pollens.

RESULTS

Results showed that the late harvest of hay, a second crop or a haylage production provides a good alternative to increase hygienic quality by reducing fungi contamination and breathable dust content. Barn drying of hay, while having no effect on breathable dust, similarly reduced fungi contamination. In contrast, when hay was harvested at a lower dry mass content (750 g DM kg⁻¹ versus 850 g DM kg⁻¹), both breathable dust and fungi contaminations were increased, which could at least be reversed by adding propionic acid just before baling. Zearalenone was detected in different hays, and even in one case, in breathable dust.

CONCLUSION

Overall, our data suggest that different approaches can be used to increase forage hygienic quality for horse feeding and thus reduce their exposure to factors involved in equine pulmonary disease.

Particle mapping in stables at an American Thoroughbred racetrack

REASONS FOR PERFORMING STUDY

Airway inflammation and mucus in the trachea are common in racehorses. Fine airborne particles can initiate and coarse particles can worsen airway inflammation in man and in animal models of airway disease. The regional and seasonal distribution of particles of different sizes has never been investigated in American racing stables.

OBJECTIVES

To determine the regional and seasonal concentration and number of airborne particles of different sizes in racing stables.

METHODS

Direct reading instruments were used to determine the mass concentration and numbers of particles 3 times daily (early morning, midday and late afternoon) in July, September and November, in 3 different racing stables.

RESULTS

Average particle concentrations were lowest in July and highest in September and November. Early morning concentrations were significantly higher than those measured throughout the rest of the day. The completely enclosed stable with little natural ventilation, had significantly higher particulate concentrations than the open-sided stable. With regard to numbers of particles, those 2-5 µm were greatest in July and least in November; those 0.5-1.0 µm were greatest in September and least in November. Location of stall within stable also affected concentrations and numbers.

CONCLUSIONS

The concentration and number of particles in sizes known to reach the lower airways varies with stable design/management, time of day, season of year and location of the stall within the stable.

POTENTIAL RELEVANCE

Particle mapping is a useful tool in the identification of stables, season, and location of stalls within stables where horses may be at greater risk of exposure to offending particulates.