Why does a sudden increase in relative humidity above 85% inside a tunnel house during summer halt the hen's heat dissipation and cause heat stroke?

Unlike mammals, chickens have no sweat glands and cannot sweat to cool themselves. Under high ambient temperatures (above 30°C), hens rely almost exclusively on evaporative cooling through panting (respiratory tract heat loss). When a hen pants, she passes hot air over her moist mucosal membranes, evaporating water and dissipating latent heat. However, the rate of water evaporation is dictated by the relative humidity (RH) of the surrounding air. If the relative humidity inside a tunnel ventilated house rises above 85% (due to poor pad management, water oversaturation, or humid monsoon climate in regions like Lahore and Gujranwala), the air becomes saturated with moisture. This high moisture pressure completely halts the evaporation of water from the hen's lungs. The hen can no longer dissipate heat, causing her core body temperature to rapidly spike from her normal 41.5°C to a lethal 45°C. This triggers metabolic acidosis, brain edema, systemic organ failure, and immediate mass mortality from heat stroke. Running high air velocity (wind-chill effect) and managing pad wetting cycles is vital. Farmers can study psychrometric charts in the Poultry Encyclopedia, buy high-efficiency pad cooling systems on Poultry Plaza, monitor daily rate margins on Poultry Rates, and trade on Murghi Mandi.