Dust in Pig Buildings
Friday, April 01, 2011
By S. Pedersen, M. Nonnenmann, R. Rautiainen, T. G. M. Demmers, T. Banhazi, M. Lyngbye. Research and review papers were presented at the international symposium on Dust Control in Animal Production Facilities, held in Denmark in 1999.
Abstract
It is well documented in the international scientific literature that airborne dust in pig houses can cause serious health problems for humans as well as for animals. Extensive research has been carried out in different countries during the last few decades to improve the scientific understanding of air quality issues related to intensive animal production.
Research and review papers were presented at the international symposium on Dust Control in Animal Production Facilities, held in Denmark in 1999. Different techniques have been used in order to reduce dust burdens in pig confinement buildings, but up to date only the procedure of spraying oil or a mixture of oil and water has contributed to reducing the indoor dust concentrations significantly. This article summarizes the current level of understanding of dust issues in intensive animal production buildings, mainly on the basis of papers presented at the above-mentioned symposium.
Concerns about the indoor environment and air pollution in pig houses have intensified over the last decades for several reasons. In contrast to the environmental conditions of former livestock houses, which were often cold and moist, modern livestock houses have been ‘improved’ by insulation in such a way that the indoor climate has become dryer, which will lead to higher concentrations of airborne dust. Large-scale production has turned pig production into a full-time occupation. Therefore, today’s workers are more frequently and extensively exposed to dust than in the past. Pig producers and the industry are increasingly aware the of Occupational Health and Safety issues.
The current level of understanding related to dust in animal houses is described in this article, mainly on the basis of papers presented at the symposium of Dust Control in Animal Production Facilities, held in Aarhus, Denmark, 1999 (Dust Control, 1999).
Sources of Dust
Dust in pig buildings is a complex mixture of particles of organic and inorganic origin and different gases absorbed in the aerosol droplets. The sources and components of dust are diverse and might include a range of microorganisms and their cell wall components, dried dung and urine, skin flakes, grain mites, spores, pollens, feed and bedding particles; whereas, the dust from incoming fresh air will be negligible in most cases. The solid components of dust can act as a transport vector for noxious gases, microbial products and components (such as endotoxin, betaglucan and peptidoglucans), ensuring that they are inhaled deep into the lungs (Morrison et al., 1993).
Characterisation of Dust
Dust can be evaluated on the basis of its chemical composition, e.g. inorganic and organic components. The organic part can be further divided into viable (bacteria, fungi, etc.) and non-viable components. Microorganisms may represent only a minor percentage (less than one per cent) of the number of airborne particles (CIGR, 1994) but they often have a marked negative effect on the health of livestock and of pig producers.
Chemical composition
Aarnink et al. (1999) investigated the composition of dust from different sources in respect to their chemical composition (see table 1).
The airborne and the settled dust have nearly the same concentrations of dry matter, ash, N, P, K, Cl and Na. In feed dust, the content of ash and P is relatively low and in faeces the content of Cl is very low, compared to Cl in skin particles. It was concluded that dust in rooms for rearing pigs mainly originates from feed and skin particles, when the mass is considered.
Microorganisms
The concentration of airborne microorganisms in animal houses is high. According to Hartung and Seedorf (1999), the incidence of CFU (colony forming units) of bacteria, expressed as log-values, was 5.1 log CFU/m3 for pigs, which is less than for poultry (6.4 log CFU/m3) and higher than for cattle (4.3 log CFU/m3). In the same investigation the mean daily concentration of fungi was 3.7 log CFU/m3 for pigs, 4.0 log CFU/m3 for poultry and 3.8 log CFU/m3 for cattle.
Mites
Mite allergens are assumed to affect the respiratory system of humans and animals. In a population of German swine farmers with work-related respiratory symptoms (Radon et al., 1999), the concentration of storage mite (Lep d 2) and house mite (Der p 1, Der f 1, Der 2) allergen in dust, collected from five different sampling sites, was studied in relation to the respective sensitization rates. The storage mite allergen (Lep d 2) was mainly found in the confinement houses and was abundantly distributed. This allergen was also detected in measurable concentrations in 35 out of 75 (47 per cent) farmers’ mattresses and in 6 out of 22 (27 per cent) urban mattresses. The median concentrations of Der p 1 in the farmers’ mattresses (26.88 µg/g dust) were significantly (p < 0.01) higher than in the urban mattresses (0.95 µg/g dust). The sensitization rates of the farmers to occupational allergens were low. None of the farmers were sensitised to swine epithelium.
Measurement of Dust
The spatial dust concentration in swine buildings is largely dependent on air distribution, relative locations of the dust sources, animal and human activity levels in the buildings and the presence or absence of air cleaning technologies (Wang et al., 1999). There is a high variation in the pattern of dust spatial distribution in mechanically ventilated pig buildings. Ventilation systems have direct effects on the spatial dust distribution. An increased ventilation rate will not necessarily reduce the overall dust level effectively, because the dust production rate will increase with increasing ventilation. The overall dust levels will generally be higher during the day than during the night, due to the animal activity that will increase the airborne dust concentration, as shown in figure 1 (Pedersen and Takai, 1999).
According to Nonnenmann et al. (1999), there is a strong linear relationship between the total weight of the pigs in the room and the dust concentration. The dust concentration more than doubled as the pigs grew during the 16-wk finishing period. Therefore, the amount of animal mass found in the building will be a major factor influencing the dust concentration.
Studying and modeling the behavior of dust in animal houses will be difficult because of the non-homogeneous nature of the dust. At the Silsoe Research Institute (Wathes et al., 1999), artificial pig dust is being developed on the basis of the main constituents of pig dust, i.e., feed, straw, and manure. Future opportunities may be gained by using the ‘Artificial piggery dust’, not only in research into pig respiratory diseases but also in studies of dust kinetics.
Contrary to heat production of domestic animals, which mainly depends on the number, size and production level of the animals, dust ‘production’ very much depends on the indoor relative humidity levels under North European climatic conditions. In poorly ventilated animal houses, the indoor surface humidity will be high, and consequently, the dust formation will be low. At increased ventilation the indoor humidity will drop, and the airborne dust concentration will increase. Therefore, it cannot be concluded that a reduction in indoor dust concentration can be obtained by increasing the ventilation level. However, in the case of natural ventilation and at extremely high ventilation rates in mechanically ventilated buildings, the dust concentration will drop. It is also important to know that dust emissions from animal houses will increase at excessive ventilation rates.
Dust concentration measurements are often carried out by means of gravimetric systems. ‘Total dust’ means the fraction containing particles below 20µm in aerodynamic diameter, collected by use of 38-mm filter cassettes with 5-mm downward inlets. The fraction collected by use of a cyclone pre-separator (50 per cent cut-off effectiveness value of 5µm) is called ‘respirable dust’. IOM samplers with a 25-mm filter and a 15-mm inlet are commonly used. In this case, particles slightly larger than 20µm will be included and this fraction is referred to as ‘inhalable dust&rdsuo;. Unfortunately, it is not possible to make a conversion from total dust to inhalable dust and vice-versa but as a rule-of-thumb the inhalable dust concentration will be about 25 per cent higher than the total dust concentration but it very much depends on the particle size distribution.
The aerodynamic diameter of particles is an important parameter for penetration of particles into the respiratory system. The aerodynamic particle size distribution of particles can be measured by use of a cascade impactor, e.g. with an Andersen six-stage sampler or an optical particle counter.
For humid environmental conditions, an alternative method based on counting liquid-dispersed livestock dust by means of an optical particle counter is described by Seedorf et al. (1999). The system allows measurement of dust in experiments with, for example, bio-scrubbers. Because the properties of dispersed dust particles may differ from those of dry dust particles, calibration of the equipment will be needed.
An overview of typical dust and endotoxin concentrations measured in North European animal houses is given by Takai et al. (1998, 1999) in table 2.
For comparison, the inhalable dust concentration measured in the same project was only 0.38mg/m3 for cattle; whereas, it was 3.60 mg/m3 in broiler houses.
In western France, a study was carried out in 18 pig units (Guingand, 1999) to establish dust concentrations in farrowing, post-weaning and finishing rooms, as shown in table 3. Dust concentrations were lower in units with liquid or granular feed than in units with meal feed and lower in units with plastic slatted floors than in units with concrete slatted floors. For example in a post-weaning unit with a ventilation rate of above 14 m3/h per pig where the feed consisted of pellets, the inhalable dust concentrations were 8.2 and 1.6 mg/m3 in post-weaning units with concrete and plastic slatted floors, respectively.
Dust concentrations increased with the age of pigs in post-weaning and finishing units. For farrowing units, the dust concentration was much lower before farrowing than close to the time of weaning. It has been suggested that the type of flooring and the feed presentation might help to limit dust concentrations in pig buildings.
In the Australian National Air Quality and Housing Survey (Banhazi and Cargill, 1999), the environmental quality and concentration of airborne pollutants within a substantial number of different classes of pig buildings were measured in four states of Australia. The results showed that the concentration of total airborne dust ranges from 0.25 to 10mg/m3 (mean 1.85 mg/m3), and the concentration of respirable particles ranges from 0.01 to 2.13mg/m3 (mean 0.27mg/3). It was also evident from the data analysis that pig shelters with straw bedding showed significantly higher concentrations of total and respirable particles, i.e. 2.44 and 0.68mg/m3, respectively, than other types of pig buildings. One important finding of the study was that the dust levels were very closely related to the standard of hygiene in the buildings.
Dose Response and Control Standards
Numerous articles have been published regarding the adverse respiratory health consequences of working in intensive livestock and poultry houses. Threshold exposure limit guidelines are not always applied in the intensive animal industry, but they are essential for the implementation and monitoring of effective environmental control strategies.
Previous dose-response studies with swine workers (Donham and Cumro, 1999) have resulted in exposure limit recommendations of 2.4mg/m3 of total dust, 0.2mg/m3 of respirable dust and a total of 800EU/m3 (EU = endotoxin unit) and 7ppm of ammonia. In an industrial study, 257 poultry workers were studied for respiratory symptoms, pulmonary function, exposure to dust (both total and respirable), endotoxin (both total and respirable), and ammonia (Donham and Cumro, 1999). A significant dose-response relationship between exposures and pulmonary function decrements was observed over a work shift. Threshold concentrations were identified as follows: 2.5mg/m3 for total dust, 0.25mg/m3 for respirable dust, 600EU/m3 for total endotoxin and 12ppm for ammonia. On the basis of the similarity of these findings and those from swine production, generic exposure thresholds for workers’ health in the swine and poultry industries have been proposed (Donham and Cumro, 1999).
In summary, a consistent relationship between environmental exposures in livestock buildings, lung function changes and/or respiratory symptoms in workers have been observed in four separate studies (Donham et al., 1999, 1995, 1989; Reynolds et al., 1996). These studies identified exposure-response thresholds for workers, on the basis of which exposure response thresholds for poultry and swine confinement buildings were suggested. The results for poultry and swine environments are very similar, and if slight differences were identified, the lower levels were recommended. Exposure limits for swine health have previously been recommended, and they are very similar to the limits for workers. The limits for swine health are shown in table 4 (Donham, 1991).
It is remarkable that the threshold limit for endotoxin for swine (1.540EU/m3) is much higher than the above-mentioned one for humans but it can in some way be explained by the fact that the life-time for swine is shorter than for humans, although there may be a biological effect, also from lower endotoxin concentrations. Those effects are hard to measure in swine; whereas, in humans it is easily documented by the decrease in pulmonary function.
Modelling of Dust Concentration – Indoors
Aerial dust concentrations are affected by the rate of dust production and also by the deposition and resuspension rates of airborne particles. Modeling of measured deposition and re-suspension rates of particles in animal buildings were investigated by Lengweiler et al. (1999). It was concluded that the deposition and re-suspension rates of particles correspond well with the reported literature but further investigations will be needed.
Particle movements in mechanically ventilated piggeries were examined by use of numerical simulation models and experimental verification (Lyngbye and Boon, 1999). The experiments were carried out in a full-scale experimental section of a piggery, and it was concluded that better particle generating equipment has to be developed. It was concluded that the location of the dust source and turbulence level will have a great influence on the particle concentration, even at an air exchange rate of 45 times per hour.
Dust Reduction Techniques – Outdoors
Windbreak walls and wet pad scrubbers
The practicality of using windbreak walls and wet pad scrubbers for reduction of odorous dust emissions from tunnel ventilated pig buildings was investigated by Bottcher et al. (1999). At a swine finishing farm downwind from building exhaust fans a full-scale windbreak wall system was built.
It was demonstrated that windbreak walls placed at three and six metres, respectively, from the building, deflected the airflow from the exhaust fans in the upward direction, similar to other wind barriers, thus providing surfaces for dust deposition. The vertical height at which the plume would flow over a downwind lagoon under low wind conditions was increased by building a windbreak wall. As a result, the dust and odor levels in the area downwind from the windbreaks was lowered.
A wet pad scrubber placed in the animal house 1.2 metres upwind from the exhaust fans achieved modest reduction in dust and odour emission from the piggery building in warm weather. The results demonstrated that these control methods did not substantially challenge the existing ventilation systems by causing excessive resistance to airflow, and they would therefore be practical and useful emission control methods.
Dust Reduction Techniques – Indoors
Oil application
Application of rapeseed oil in pig buildings by means of a roller applicator during feeding or a scratching surface applicator, designed to squirt oil on contact, was tested (Osman et al., 1999). The scratching surface applicator consisted of a foam pad, which was manually impregnated with oil at regular intervals. The roller applicator was designed to apply approximately 10mL of oil per pig per day. A roller applicator installed on an ad-libitum feeder was found to be the most effective system. When compared to control facilities, significant reductions in inhalable and respirable dust concentrations of 83/63 per cent (p<0.001) and 35/32 per cent, (p<0.001) were achieved with the roller applicator and scratching surface applicator, respectively. Therefore, the roller applicator was demonstrated to be an alternative and very effective dust reduction method for oil spraying.
Oil sprinkling
In the period from 1986 to 1991, an effective dust control method with dust reduction rates from 50 to 90 per cent was developed at the National Institute of Agricultural Engineering (DIAS-Bygholm), Denmark (Takai and Pedersen, 1999). The system’s feasibility in full-scale pig production systems was proven. The system relies on spraying a sufficient amount of oil in piggeries to bind dust particles, so that they will not disperse and re-suspend from building surfaces. To successfully design and install oil spraying systems for dust control in pig buildings, the following issues need to be considered:
- The oil concentration in the oil-water mixtures should be higher than 20 per cent. At this concentration, the moisture added to a barn environment would only slightly increase the indoor humidity levels, i.e. by less than two per cent.
- Droplet sizes greater than 150µm are desired to achieve a rapid deposition of droplets on available surfaces. This characteristic of the spraying system is important to improve the effective use of oil as a dust binding agent and to reduce the potential health hazard of inhaling airborne oil droplets.
Many kinds of vegetable oil for dust binding purposes are available at reasonable prices. However, there are some issues to be considered:
- It is not necessary to use refined vegetable oil but the oil should be free of particles.
- Vegetable oils with strong odour may not be suitable because of their potential effect on the animal behaviour.
- Vegetable oils with low iodine value should be used, in respect to the risk of self-ignition.
- The dust-binding effect of oil is likely to remain for many days. Spraying strategies should therefore be designed accordingly.
Several methods for reduction of aerial dust in pig houses have been examined over the last 20 years (Gustafsson, 1999; Guarino and Navarotto, 1999; Kirychuk et al., 1999; Zhang, 1999; Barber et al., 1999; Seedorf et al., 1999). To date, the most promising method appears to be oil sprinkling. In summary, the following results have been obtained:
Sprinkling undiluted canola oil in a grower-finisher room produced a dust reduction of 79 per cent. Respirable and inhalable dust particle concentrations were reduced by 73 and 80 per cent, respectively (Lemay et al., 1999).
Jacobson et al. (1999) achieved reduction of odour and dust emission by daily sprayings of soybean oil in a nursery building divided into a treatment barn and a control barn for pigs from seven to 23kg. The dosage was 40mL/m2 for the first two days, 20mL for the next two days, after which a quantity of 5mL/m2/day was used. The treatment reduced the concentration of both total and respirable dust significantly. Odour levels were 150 and 400 odour units in the treatment barn and the control barn, respectively. Hydrogen sulphide levels were also reduced significantly (55 to 65 per cent) but no influence on the ammonia concentration in the barn was detected.
Sprinkling canola oil on floor surfaces will reduce the odour and respirable dust emissions in mechanically ventilated grower barns (Feddes et al., 1999). Canola oil was applied weekly at rates of 60 and 30mL/m2 to the pen floor surfaces in a growing pig facility, and odour concentrations were measured by using a single-port, forced choice olfactometer (AC’SCENT, St. Croix Sensory, Inc., Stillwater, Minn.). The odour concentration was reduced by 20 per cent for the 60mL/m2 weekly application rate; whereas, no significant differences (three per cent reduction) were detected for the 30mL/m2 weekly application. The reduction in odour concentration was lower than the reduction achieved in respirable and inhalable dust concentrations. The odour reduction was the result of reducing airborne respirable dust particles responsible for carrying the odour volatile compounds.
Nonnenmann (1999) examined the effect of a vegetable oil sprinkling system on the dust concentrations in four pig finishing rooms. Two of them were treatment rooms (6.7g of soybean oil per pig per day in one room and 8.1g of rapeseed oil per pig per day in the other one), and the other two were control rooms. The treatment rooms were equipped with low-pressure oil sprinkling systems, which sprinkled a five per cent mixture of oil and water 12 times a day at a dose rate of 12 s.
The average inhalable dust level in the control rooms was 1.39mg/m3 and the average concentration in the treatment room was 0.65mg/m3. Dust reductions of 54 per cent (p=0.0001) were obtained. The respirable dust concentrations were very low in all rooms, and there were no significant differences in carbon dioxide, ammonia, temperature and humidity between the rooms. Both types of oil performed equally well in this experiment.
Although a considerable reduction in dust can also be achieved by adding fat to pig feed, sprinkling of oil has so far proven to be the best technique for reduction of dust levels in pig production systems. In figure 2, the achievable dust reductions of various methods are summarised.
Conclusion
Different airborne dust reduction techniques for animal confinement buildings have been studied worldwide over the last decades. Currently, the method of spraying oil or an oil-water mixture in animal confinement buildings is the most promising technique, providing significant dust reduction. It was also documented that reductions of up to 50 per cent can be obtained by adding five per cent of fat to the feed. In order to improve the overall environmental quality of animal houses, more research on animal behaviour is needed, if production efficiency, animal and human health and animal welfare are to be improved.
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