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Highlights

Building characteristics (ventilation and animal density) seem to have an important effect on air quality.

Abstract. Alternative farming methods make it possible to satisfy public demands for animal welfare while preserving production efficiency, with free housing in dairy farms being an example. The increased movement of cows may have a negative impact on air quality and the presence of etiological agents, increasing the prevalence of lung disease in workers. Free-stall farms, however, are more spacious and modern than tie-stall farms. This study characterizes air quality in free-stall and tie-stall farms (dust, total bacteria, Penicillium/Aspergillus, archaea, and endotoxins). It also focuses on detecting airborne etiological agents and indicators of fecal contamination, as well as assessing the effect of environmental factors on air quality. Five farms of each type (free housing and tie housing) using straw bedding material and equipped with mechanical ventilation were visited. Sampling visits were conducted in winter with no activity (e.g., bedding spreading) in buildings. Dust was evaluated using the DustTrakTM DRX Aerosol Monitor, and bioaerosols were sampled in triplicates for 10 minutes using the SASS®3100 Dry Air Sampler. Finally, soiled bedding was collected throughout the barn. No type of housing seems to be linked with poorer air quality, but some air quality indicators stood out in some outliers. The most recently designed free-housing buildings and the greater air volume may have played a role in the absence of detected differences. Escherichia coli, Enterococcus spp., Clostridium perfringens, Aspergillus fumigatus, Staphylococcus aureus, Saccharopolyspora rectivirgula, Coxiella burnetii, and Klebsiella pneumoniae were detected in high concentrations in both types of buildings. Soiled bedding concentrations, ventilation rates, and animal density seemed to have a significance on air quality in dairy barns.