On Day 30, broilers reach ~1,925g and produce immense biological heat (~10-12 Watts of metabolic heat per bird). As feather coverage is complete and subcutaneous fat builds, sensible heat loss becomes impossible when ambient temperatures surpass 26°C. Farmers must rely entirely on tunnel ventilation air velocity for wind chill and controlled evaporative cooling. Water line flushing is essential to prevent hot water refusal, and feed must be managed during peak afternoon temperatures.
Heat stress in heavy finishing broilers causes rapid respiratory alkalosis, panting exhaustion, heat stroke, and mass mortality within 60 minutes of fan or power failure. Proper tunnel air speed lowers the bird's effective temperature by 4–6°C.
•Running cooling pads continuously at high humidity (>80% RH), creating a deadly sauna effect inside the shed.
•Allowing water lines to heat up in roof or perimeter piping so birds drink warm water, which accelerates heat collapse.
•Feeding full rations during peak afternoon heat, triggering lethal digestive thermogenesis.
•Leaving dirty louvers on exhaust fans, which reduces air speed across bird backs by up to 30%.
•Respiratory alkalosis occurs during prolonged heat panting as birds exhale excess CO2, disrupting blood pH and mineral balance. Adding sodium bicarbonate (0.1–0.2%) and potassium chloride to water restores electrolyte equilibrium.
•Veterinary escalation trigger: If core body temperature of sampled birds exceeds 43.5°C (rectal thermometer) or heat prostration mortality exceeds 0.1% in an afternoon, immediately initiate emergency cooling and consult veterinarian.
•Place your bare forearm at bird height in the center of the shed. You should feel a distinct, cooling breeze against your skin. If you feel stale, still air, your birds are suffering.
•Never run water through cooling pads early in the morning when humidity is high. Wait until the afternoon heat drives humidity down below 75% before wetting pads.
Digesting feed generates substantial internal body heat (specific dynamic action). Withdrawing feed 2-3 hours before peak heat prevents metabolic heat overload, saving heavy birds from acute heat prostration.
Drinking water must remain below 24°C. Above 26°C, broilers reduce water intake; above 30°C, they refuse water entirely, triggering swift dehydration and fatal heat stroke.
