Indoor livestock — pigs, poultry, and housed cattle — depend entirely on artificial ventilation for air quality and thermal comfort. Ammonia from manure accumulates rapidly in poorly ventilated buildings, causing respiratory damage, eye irritation, and immune suppression at concentrations above 20 ppm.
High temperatures combined with humidity cause heat stress in all livestock species. Cattle begin experiencing heat stress above 22°C THI; pigs above 25°C; poultry even lower. Fans, evaporative cooling, and roof sprinklers are welfare interventions in hot climates. Climate change is making heat stress more frequent and severe.
Naturally ventilated buildings use wind and thermal buoyancy to move air through inlets and ridges. They are lower cost but variable — unsuitable for high stocking densities or extreme climates. Mechanical ventilation with automated controls maintains consistent air quality regardless of outside conditions.
Ammonia causes ciliary damage in the respiratory tract, impairing pathogen clearance and increasing BRD risk in cattle and pigs. Maintaining litter quality in poultry houses, slat cleanliness in pig systems, and adequate air exchange rates all reduce ammonia concentration. Target: below 10 ppm continuously.
In pig slaughter, CO2 stunning using concentrations of 70-90% causes significant distress (dyspnea, aversion) before unconsciousness. Ventilation during stunning is paradoxical — sufficient CO2 for unconsciousness causes welfare-relevant distress. Low atmospheric pressure stunning and alternative gases are active research areas.
Livestock welfare audit standards now include ventilation performance checks: ammonia measurements, temperature monitoring, and behavioral indicators of thermal discomfort (huddling, panting, spreading). Automatic climate controllers with welfare alerts are becoming standard in high-welfare production systems.