Particulate matter (PM), also known as dust, is one of the most perceived air quality issues in swine barns. PM is considered an air hazard by the Occupational Safety and Health Administration (OSHA). Although PM monitoring or survey is not being taken in commercial barns on regular basis, many producers are well aware of the importance of keeping barns clean (and less dusty). PM can carry a variety of hazardous substances such as pathogens and odors. A dusty barn (with high PM concentrations) would therefore compromise animal and human health and deteriorate the environment. Decades of academic research have greatly advanced our knowledge of PM in swine barns. This report intends to review and present these advances to the U.S. pork industry.

The review covers four topics: PM characteristics (e.g., concentrations and germs), sources, measurement methods, and mitigation technologies. A total of 380 academic publications were compiled from various sources, many of which were published after 1990. Our major findings are listed below:

  • PM concentrations are highly variable in swine barns. In very dusty barns, the concentrations of total dust (TSP) can exceed 20 mg m-3; while in clean barns, the concentrations can be as low as 0.15 mg m-3. PM concentrations are generally higher in winter and lower in summer, and increase with elevated animal activity. PM concentrations can be different at different spots inside a swine barn. Fine PM is of particular concern for its capability of reaching the lung of human workers and pigs. Relevant regulations are enacted through OSHA and the U.S. Environmental Protection Agency (EPA), with extensive monitoring data available from previous research.
  • PM concentrations in swine barns can be mitigated with four types of technologies: oil/water sprinkling, ionization, alternation of feed and feeders, and recirculating air filtration. These technologies have been extensively tested, with effectiveness ranging from <10% to >90%. However, no extensive use of these technologies on commercial farms has been reported. Oil/water sprinkling, ionization, and recirculating air filtration have also been tested for their reduction in airborne bacteria, with decent efficiency reported.
  • PM in swine barns comprises primarily large particles, with diameters greater than 10 µm. But fine and ultra-fine particles (e.g., particles smaller than 1 µm) also exist. The density of PM ranges from 1,400 to 2,100 kg m-3, with an average value of 1,650 kg m-3 (103 lb ft-3). Because of the relatively large size and density, many dust particles in swine barns would quickly settle down to the floor or ground. PM size in swine barns tends to be greater in summer than winter and be greater in sow barns than other barns.
  • PM in swine barns comes from three dominant sources: feed, feces, and skins. For barns with bedded floors, bedding material can be another major source. Feed is generally considered as a primary source of large particles; while feces are thought to be a chief source of fine particles. This again supports the idea of using altered feed and feeders for PM mitigation and suggests the importance of manure and feed spillage management for PM control.
  • PM can carry and amplify odors. A total of 159 odorous chemicals have been identified in swine barn PM samples, the majority of which are volatile organic compounds (VOCs). Many of those odorous chemicals are produced from the anaerobic decomposition of swine feces. In addition to hydrogen sulfide and ammonia, the identified malodorous chemicals include indole, skatole, and methanethiol. Fine PM is especially problematic. As it originates from feces, fine PM contains a higher abundance of odorous chemicals than coarse PM.
  • PM in swine barns also carries biological agents known as bioaerosols. These include bacteria, fungal spores, viruses, endotoxin, and (1→3)-β-D-glucans. Numerous efforts have been devoted to bioaerosols research for their significant implication for animal and human health. Regarding bacteria and fungi, their concentrations in the air have been extensively measured. Culturable bacterial and fungal counts are up to 1.82×1010 and 7.24×106 colony-forming unit (CFU) m-3, respectively, in swine barns. Total bacterial and fungal counts are even greater. Airborne bacteria in swine barns tend to bind to large PM; whereas fungi (molds) appear to exist as individual particles.
  • Numerous bacterial and fungal species have been identified in the air of swine barns from microbial composition analysis, including pathogens and potential pathogens that threaten pig and human health. Some airborne bacteria have a clear association with microorganisms in pigs’ gastrointestinal tracts, suggesting their fecal origins. Antibiotic-resistant bacteria (ARB) have also been detected, as well as antibiotic resistance genes (ARGs). An example of ARB is methicillin-resistant Staphylococcus aureus (MRSA).
  • Previous research has identified the presence of several major porcine viruses [e.g., influenza A virus (IAV) and porcine reproductive and respiratory syndrome virus (PRRSV)] in the air of swine barns, indicating the possibility of airborne viral transmission. PM sampling and analysis may serve as a tool for the field surveillance of porcine viruses; however, further research is needed to validate its usefulness. Efforts have also been made to develop and test mitigation technologies for airborne porcine viruses.
  • Endotoxin, a marker for gram-negative bacteria with known health effects, has been extensively monitored in swine barns. Airborne endotoxin concentrations generally reach the highest level in nursery barns and the lowest level in sow barns and are typically greater in winter than summer. Other investigated bioaerosol markers include (1→3)-β-D-glucans and total proteins. However, their health implication has yet to be established. Relevant monitoring data are sporadic in the literature.

The target audience of this report includes animal scientists, veterinarians, pork producers, agricultural engineers, and air quality professionals. It contains many technical details and information compiled from multiple disciplines. The goal is to further profound our understanding of PM in swine barns and develop cost-effective management strategies, thereby promoting the healthy and sustainable development of the U.S. pork industry.