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There is much information about the concentrations and emissions of ammonia in livestock production facilities in Europe and North America; examples of best and worst practice have been identified in terms of building design and environmental management. Numerically, cattle are the largest source of ammonia emissions, while the ammonia concentration in swine and poultry buildings is much higher than in cattle sheds.

In this paper, we review the grounds for concern over ammonia and question whether current guidelines and limits are sufficient to protect farmers, livestock and the environment. Firstly, epidemiological studies of worker health have shown that swine, and to a lesser extent, poultry workers experience occupational respiratory disease in which chronic ammonia exposure may play a part: current occupational exposure limits for ammonia are probably too high and should be revised downwards. Secondly, the scientific evidence that ammonia exposure affects animal health and performance is less convincing - though this is contrary to the empirical wisdom of veterinarians and farmers - and the guidelines are correspondingly unclear. A new guideline is provided from preference studies that show that pigs and chickens avoid ammonia concentrations above 10 ppm. Overall, only tentative guidelines for ammonia concentration can be proposed on the grounds of animal health, performance and welfare. Finally, as a result of international protocols, e.g. the UNECE convention on the long-range transport of air pollutants, individual countries are now expected to limit their ammonia emissions at a national level. This intention has not (yet) been translated into a specific limit on emission for individual farms. In the USA, but not UK, guidelines have also been suggested for ammonia concentration at the property line of animal feeding facilities.