Ammonia acts as a low-level stressor, robbing pigs of energy needed for growth. Keep room air velocities low in cool weather, because high air velocity picks up more ammonia from the manure pit or gutter surface. Farrowing and nursery rooms have the highest ammonia potential because the stored manure temperatures are highest in those. In partly slatted finishing buildings, keep the floors clean as possible, so that the pigs are not lying in wet manure. Ammonia tends to be highest in scraper-equipped rooms, followed by deep pit rooms, and lowest in gravity drain and pit recharge systems.
Dust can stress the respiratory system, by carrying adsorbed gases deep into the lungs.
Cut dust by regular thorough sanitation, adding fat or oil to the feed, keeping feed spout delivery points low in the feeder, and by careful regulation of the ventilating system in cool weather. High humidity is usually a problem in cold weather only, but high relative humidity tends to promote passage of airborne pathogens from pig to pig. This is because the aerosolized water droplets pigs sneeze and cough into the air, carrying germs, do not dessicate very fast in humid air. The germs hitchhike on the droplets to the next pig and infect it. Control relative humidity by adjusting ventilation controls settings, especially the air inlets.