Ammonia gas (NH3) is formed by the decomposition of animal waste and is present at some level in most animal facilities. The odor can be detected by most people at concentrations of around 10 ppm; a level which appears to have little detrimental effect on pig health. However, when the concentration reaches 50 ppm or more, NH3 may act as an irritant of the mucous membranes of the eyes, nasal passages, and lungs and cause ocular and nasal discharge. Concentrations of NH3 that are high enough to be irritating to mucous membranes of pig farm workers likely have a similar effect on animals continuously exposed.
Research on swine suggests that toxic concentrations of NH3 (over 50-100 ppm) reduce growth rate, reduce bacterial clearance from the lungs (interferes with mucociliary apparatus), exacerbate nasal turbinate lesions in pigs infected with Bordetella bronchiseptica and may influence the course of infectious diseases.