Exposure to pollutants and biological aerosol in indoor facilities for horses

With repeated use, it has always surprised me how dusty sand can become in an indoor arena as it breaks down. If you can smell the urine or see the dust it is too much for optimal respiratory health for horses. Adequate replacement of bedding and flooring materials, wetting down of working surfaces when in use, and excellent ventilation are not just important but essential.
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Exposure to chemical pollutants and biological aerosol in indoor facilities for recreational and sport horses
BMC Vet Res. 2024 Feb 28;20(1):78. doi: 10.1186/s12917-024-03930-2.
Authors
Izabela Rodzyń 1 , Katarzyna Karpińska 2 , Hanna Bis-Wencel 1 , Łukasz Wlazło 1 , Mateusz Ossowski 1 , Katarzyna Strzelec 3 , Sebastian Jaguszewski 4 , Bożena Nowakowicz-Dębek 1
Affiliations

1 Department of Animal Hygiene and Environmental Hazards, Faculty of Animal Sciences and Bioeconomy, University of Life Sciences in Lublin, Akademicka 13, Lublin, 20-950, Poland.
2 Department of Animal Hygiene and Environmental Hazards, Faculty of Animal Sciences and Bioeconomy, University of Life Sciences in Lublin, Akademicka 13, Lublin, 20-950, Poland. katarzyna.karpinska@up.lublin.pl.
3 Department of Horse Breeding and Use, Faculty of Animal Sciences and Bioeconomy, University of Life Sciences in Lublin, Akademicka 13, 20‑950, Lublin, Poland.
4 Student Scientific Association of Occupational and Environmental Hazards, Faculty of Animal Sciences and Bioeconomy, University of Life Science in Lublin, Akademicka 13, 20‑950, Lublin, Poland.

PMID: 38413934
DOI: 10.1186/s12917-024-03930-2

Abstract

Background: Due to the increasing prevalence of equine non-infectious respiratory disease, the air contamination in equine housing (Stables A-C) and training facilities (indoor riding arenas A – C) was investigated. The aim of the study was to monitor gaseous pollutants, bioaerosols, and dust concentrations at three different sites (stables and riding halls), where different floor materials were used in the riding halls.

Materials and methods: Air quality was monitored in housing for horses and in riding halls in terms of dust concentration, the presence of gaseous chemical pollutants, and concentrations of biological aerosol. Statistical analysis was performed using analysis of variance (ANOVA). The levels obtained were compared with acceptable limits.

Results: Among the gaseous pollutants identified, the highest concentration was obtained for ammonia in stables B and C (16.37 and 22.39 mg/m3, respectively). Standards for total dust were exceeded in stables B and C and in riding halls B and C. The highest numbers of bacteria and fungi were recorded in stables A and C and in riding hall B. Ulocladium sp. had the highest percentage share among the moulds identified.

Conclusions: The results confirm that the wrong choice of bedding in the stable and indoor riding arenas may contribute, even in short training periods, to equine non-infectious respiratory disease (equine asthma). Bioaerosol suspended in the air together with released gaseous pollutants can exacerbate this phenomenon, which even in the case of short training periods can lead to equine asthma of varying degrees of severity. For this reason, the choice of floor material in riding halls should be treated as a priority, as the wrong decision can shorten the period during which the horse can be used for recreational purposes.

Keywords: Bioaerosols; Chemical hazards; Dust concentration; Riding hall; Stables.
© 2024. The Author(s).

Discussion
Air quality is a very important factor influencing the occurrence of respiratory disease in horses, hence the high level of interest in the effect of the floor material in the riding hall where training takes place and bedding in the boxes where the horses rest [22]. White et al. [23] report that there are numerous allergens in the horse’s environment which can lead to severe equine asthma (sEA). Asthma in horses limits their use. Air quality is determined by numerous factors, including the quality of the feed, the type of bedding, the floor material used in riding halls and how often it is changed, and maintenance of cleanliness in the boxes and paddocks [24, 25]. Relationships are observed between the presence of organic and respirable dust and chronic bronchitis in riding instructors, which suggests that horses can be an excellent model for assessment of the quality of this environment [26]. Particular attention should be paid to the riding hall, where during increased physical activity the animal takes in more air, and with it increased levels of harmful chemical and biological agents. This problem concerns artificial surfaces as well [17, 26, 27]. In stables during winter, the relative humidity should not exceed 80%, assuming that the temperature in the stable is less than 10oC [28]. In studies by Elfman et al. the average level of dust concentration was 0.6 mg/m3 [28]. Referring to the Swedish guidelines for horses (10 mg/m3), the obtained total dust values in our own research did not record any exceedances of these values, with the exception of riding school C [29].

According to the European Committee for Standardization (Comité Européen de Normalization), the smaller the particle size (< PM 0.1), the greater risk the particles pose to the body, as they diffuse to the lower respiratory system and penetrate the alveoli. Therefore, assessment of biological aerosol and dust concentrations in stables and riding halls must take into account the size of the particles in the air. Wheeler et al. [30], in a study conducted in equestrian arenas, showed that in a riding hall with a sand floor, 60% of the dust collected was respirable. In riding halls, A and C, the percentage of respirable dust during training of horses was higher than at site B. Gesche and Engel [17] demonstrated interactions between dust concentrations and the month of the year as well as the time spent by the animals in the riding hall. The authors point out that moistening the surface can reduce the dust concentration in the air. The German Senate Standing Committee on the Investigation of Harmful Working Materials (Ständige Senatskommission zur Prüfung gesundheitsschädlicher Arbeitsstoffe) gives normative values for individual dust fractions. The acceptable concentration of the respirable fraction of granular dust was determined to be 0.3 mg/m3, while the limit for the total dust concentration is 4 mg/m3. In the present study, these recommended levels were exceeded in stables B and C. Using the MS Excel Solver model in relation to the acceptable levels, safe time periods for horses in air with sustained long-term dust concentrations were obtained. The presence of suspended particulates (PM 10 and PM 2.5) in the horses’ breathing zone is conducive to the accumulation of mucus in the trachea and an increase in inflammatory cells. In addition to dust, Penicillium spp., Cladosporium spp. and Aspergillus spp. are often suspended in the air [16, 17, 31]. For this reason, it is important to pay attention to the air exchange in the stable and, at the planning stage, to the orientation of the stable. In the present study, Ulocladium spp. and Aspergillus spp. had the highest percentage shares of the moulds. Moulds of the genus Ulocladium spp. are found in feed, air, soil, and even building materials, carrying out biodeterioration [32]. The presence of this biological aerosol depends on the quality of feed, the sanitary condition of the facilities, and microclimatic conditions. Due to the use of horses for sport and recreational purposes, there is a need to monitor the air quality, especially during training sessions in the riding hall, in order to reduce the horses’ exposure to dust particles on which bioaerosol is suspended. Keeping in mind that workers are also exposed to these pollutants [33]. Optimal microclimatic conditions positively influence the welfare of horses. These levels were maintained in the present study [34]. It should be borne in mind, however, that ammonia is generated from the degradation of nitrogen compounds in manure and from conversion of urea by urease and microorganisms present in bedding [20]. According to Elfman et al. [28], Ivester et al. [11], and Saastamoinen et al. [35], the ammonia concentration in the building is influenced by the bedding in the stable and the floor material in the riding hall. Inhalation of ammonia by horses, especially those used for sport and recreation, can lead to conjunctivitis and also increases susceptibility to respiratory disease. At low concentrations, ammonia mainly affects the upper respiratory tract, while increased concentrations and prolonged exposure lead to metabolic disorders of the liver and secretion in the form of urea. Intensive use of horses, especially sport horses, can furthermore lead to oxidative stress and have a negative impact on welfare [36]. Biological (fungi) and chemical agents (PM 10, PM 2.5, NO, NO2, and SO2) in the air play a major role in diseases of the lower and upper respiratory tract. Training causes the horse to take in more air, and physical exertion results in bronchodilation and an increase in the respiratory rate and tidal volume. NO plays an important role in regulating airway function by signalling that the airways are relaxed. It also regulates the animal’s immune response and controls the release of various inflammatory substances involved in inflammatory responses. Their concentration in the air may be a biomarker of the respiratory [37,38,39]. Araneda [40] observed that air pollution affects the performance of horses used for sport and draws attention to a wide range of effects of inhaled air components on the body. According to Whittaker et al. [41] in stables and riding halls with an efficient ventilation system the main factor determining exposure to air pollutants and respirable dust is the floor material and feed [42]. Mönki et al. [22] demonstrated that the floor material and suspended compounds in dust are significantly linked to the occurrence of equine asthma in horses. Similar results were obtained by Fleming et al. [43] in a study of respirable dust from various floor materials. PM 10 and PM 2.5 levels were highest for litter consisting of hemp and flaxseeds and lowest for straw pellets, wood shavings, paper cuttings, and straw. In the present study, the highest total dust concentration was obtained in the riding halls using sand, sawdust and gravel (RHB and RHC), as confirmed by Wheeler et al. [30]. The authors report that increasing the moisture in the floor material in the riding hall improves air quality. Mönki et al. [44] found that peat bedding causes fewer cases of respiratory inflammation in horses than wood shavings. An increase in the concentration of pollutants in the air increases inhalation exposure in horses. According to Whittaker et al. [41] the respirable dust fraction in the stable can account for 30% to even 60% of total dust, and the indoor dust concentration increases in winter [11] which is in agreement with the present study. In the literature on maintenance conditions for horses used for recreation, there are few studies on the problem of the accumulation of inhalation hazards in stables, not only microbiological contaminants, but also chemical contaminants and dust. The synergistic effect of these factors, however, is of great importance in animals such as horses, which have a sensitive respiratory tract. Among the many chemical compounds identified, the respiratory system of horses is most threatened by ammonia, which can synergistically magnify the toxic effect of the high dust concentrations in the air. The other gaseous pollutants identified (trace gases) may enhance this harmful effect. Animal welfare may be additionally harmed by high concentrations of microscopic fungal spores, which are one of the main groups of inhalant allergens. Given the existing threat to the respiratory system of horses, there is a need for monitoring and for measures to improve air quality through the choice of bedding material and hygiene in indoor facilities. Conclusions Among the chemical air pollutants identified, ammonia remains the gas of greatest concern. Its concentration is variable and depends on both management and conditions of horse maintenance. The problem of harmful gaseous pollutants may be compounded by an increase in total dust concentrations, exceedances of which have been recorded in both the stable and the C riding arena. According to the study, the age of the facility is an important factor affecting the condition and degree of dust and chemical pollution. Concentrations of bacterial and fungal aerosol obtained the highest values precisely in the oldest facility. The results indicate that it is necessary to modernize the facilities where horses are housed, appropriate selection of the substrate in the dressage halls to avoid respiratory health problems during the use of animals. In addition, when planning the recreational use of horses, it is advisable to control the microclimatic conditions in the premises to maintain the welfare of the horses. 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