Why Heat Stress Is a Fast-Acting Profit Killer
Heat stress is one of the most dangerous and costly conditions in broiler production because it can escalate from normal to catastrophic in a matter of hours. Birds cannot sweat — they cool themselves through panting and by reducing activity. When ambient temperature approaches or exceeds body temperature (106–107°F or 41–42°C), their cooling mechanisms become inadequate, and core body temperature rises. Mortality from acute heat stress can reach 10–30% in a single afternoon if ventilation systems fail or are inadequate for the conditions.
Beyond acute mortality, chronic low-grade heat stress — where birds are uncomfortable but not dying — causes economic damage through reduced feed intake, worse FCR, impaired immune function, and poorer meat quality at processing. The effects of heat stress are cumulative, and birds that experience repeated hot days may never fully recover their growth trajectory.
Understanding Heat Stress Risk Factors
Heat stress risk depends on the interaction of temperature and humidity. The temperature-humidity index (THI) is a better indicator of heat stress risk than temperature alone. At a THI above 80, birds begin showing signs of heat stress. At a THI above 90, mortality risk is high. High humidity reduces the effectiveness of both panting and evaporative cooling, making humid heat waves significantly more dangerous than dry heat waves at the same temperature.
Bird age and weight also affect heat stress susceptibility. Heavier birds produce more metabolic heat and have a smaller surface-area-to-volume ratio, making heat dissipation harder. A 6-pound bird in week 6 is far more vulnerable to heat stress than a 1-pound bird in week 3 at the same temperature.
Using Tunnel Ventilation and Cooling Pads
Tunnel ventilation creates wind-chill cooling that can reduce effective bird temperature by 10–15°F. The target airspeed for heat stress management is 500–700 feet per minute. At these speeds, birds experience significant cooling even when air temperature is in the 90s.
Evaporative cooling pads can reduce incoming air temperature by 10–20°F, depending on outside humidity. For cooling pads to be effective, they must be maintained properly — cleaned of scale and debris at the start of each hot season, checked for uniform water distribution across the entire pad surface, and replaced when pad deterioration reduces cooling efficiency. Cooling pads typically last 3–5 years with proper maintenance.
Fogging systems provide supplemental cooling in houses without pads or during extreme conditions. High-pressure fogging nozzles atomize water into fine droplets that evaporate in the air, reducing temperature. Foggers should be used in combination with adequate ventilation to prevent excessive humidity buildup inside the house.
Water Management During Heat Stress
Water consumption can increase by 50–100% during heat stress periods. A flock of 20,000 six-week-old birds may consume 2,500–3,500 gallons per day during hot weather, compared to 1,500–2,000 gallons under normal conditions. Growers must ensure adequate water supply, pressure, and flow rate to meet this increased demand.
Water temperature matters — birds prefer cool water (55–65°F). Water that is too warm reduces intake at the time when birds need it most. Flushing drinker lines several times during hot afternoons keeps water cool and fresh. Adding electrolytes to the water can help replace minerals lost through panting and support bird recovery during heat stress events.
Emergency Heat Stress Protocol
Every grower should have a written emergency heat stress protocol that is implemented automatically whenever the forecast calls for high temperatures. Key elements include confirming all tunnel fans are operational and clean, verifying cooling pad pumps are functioning and pads are wetted evenly, checking emergency generators and automatic changeover systems, increasing water line flushing frequency to maintain cool water, reducing feed presentation during the hottest part of the day (feed digestion generates metabolic heat), and conducting more frequent house checks during peak temperature hours.
Logging Heat Stress Incidents
Recording heat stress events — date, temperature, humidity, ventilation settings, mortality, and actions taken — creates a record that helps growers prepare for future events. If a particular house consistently shows higher mortality during heat waves, it may need ventilation upgrades or additional cooling capacity. Without records, growers cannot distinguish between a bad day and a systemic problem that needs correction.