Ammonia concentration and recommended threshold values in pig farming: a review

Intensive pig farming is a source of ammonia, particulate matter and other pollutants as hydrogen sulfide, greenhouse gases, and odors. In particular, high concentrations of ammonia and particulate matter inside pig buildings cause a deterioration of air quality with effects on pig health and productivity, as well as increasing respiratory problems, sensory irritations in eyes, throat, and nose for both animals and stockmen. Furthermore, when the pollutants, produced inside the pig buildings, are released in the environment they can cause acidification of soil, eutrophication of terrestrial and aquatic ecosystems, climate change, etc. The aim of this study was to make an overview of the concentration level and variations in ammonia emissions in pig houses reported in the literature. Additionally, it has been verified that the concentration level reported in the selected papers comply with the threshold values provided by the literature, and, finally, some acknowledged mitigation strategies to reduce indoor production, concentration, and outdoor emissions of airborne contaminants are summarized. Higher concentrations were measured in farms where the pigs were housed with a forced ventilation system. Some variables like the weight of the animals, slurry management, feeding method, and indoor environmental conditions can determine differences among values recorded in farms with the same floor type. By comparing the data reported in the literature, it is possible to observe that the recorded values are usually lower than the recommended thresholds.