💡 Executive Summary: Beating Summer Heat Stress
- Chickens Cannot Sweat: Poultry rely entirely on evaporative cooling through panting. When ambient temperature exceeds 30°C (86°F), panting increases CO₂ loss, causing blood respiratory alkalosis.
- Tunnel Ventilation Target: Maintain air speed across birds at 2.5 m/s to 3.0 m/s (500–600 ft/min) to produce a 5°C–7°C wind-chill cooling effect.
- Evaporative Cooling Pads: Run evaporative pad pumps when house relative humidity is below 75% to drop inlet air temperature by 4°C to 8°C.
- Night Feeding Schedule: Withdraw feed during peak afternoon heat (12:00 PM – 4:00 PM) and offer feed during cooler night hours to reduce metabolic heat increment.
1. Avian Thermal Physiology
Unlike mammals, chickens have no sweat glands. Their normal core body temperature is 41°C (105.8°F). Heat dissipation occurs primarily through sensible heat loss (radiation and convection) at normal temperatures, but shifts entirely to evaporative panting when ambient temperature crosses 27°C (80°F).
2. Heat Stress Symptoms & THI Index
The Temperature-Humidity Index (THI) measures thermal stress by combining dry-bulb temperature and relative humidity:
| Temperature (°C / °F) | Relative Humidity (RH) | Heat Stress Severity Level | Observed Bird Behaviors |
|---|---|---|---|
| 20°C – 24°C (68°F–75°F) | 50% – 65% | Thermal Comfort Zone | Normal feeding, active movement, smooth respiration |
| 27°C – 30°C (80°F–86°F) | 60% – 75% | Alert / Mild Stress | Slight panting, spreading wings away from body |
| 31°C – 35°C (88°F–95°F) | > 70% | Moderate to Severe Stress | Rapid panting, feed refusal, resting on litter, egg shell thinning |
| > 36°C (97°F+) | > 75% | Emergency / Mortality Risk | Prostration, cyanotic combs, acute mortality from cardiovascular failure |
🌡️ Calculate Barn Temperature-Humidity Index (THI)
Use our live THI Calculator tool to monitor heat stress risk in real-time and receive automated cooling alerts.
Launch THI Calculator Tool ›3. Tunnel Cooling Pads & Air Speed
In closed climate-controlled houses, tunnel ventilation exhaust fans pull air through wet cellulose cooling pads installed at the opposite end of the building. To maximize wind-chill cooling:
- Ensure tunnel fans achieve an air velocity of 2.5 to 3.0 m/s at bird height.
- Do not run cooling pad pumps if barn relative humidity exceeds 80%, as high humidity prevents moisture evaporation from pads and exacerbates bird panting.
4. Summer Feeding & Electrolyte Supplementation
Hyperventilation (panting) causes birds to exhale excessive carbon dioxide (CO₂), lowering blood carbonic acid and elevating blood pH (respiratory alkalosis). This disrupts blood calcium binding, causing thin eggshells in layers and poor bone mineralisation in broilers.
- Sodium Bicarbonate (0.25% to 0.5% in feed): Restores blood bicarbonate levels and improves eggshell thickness during heat waves.
- Vitamin C (Ascorbic Acid @ 150–200 g/ton): Reduces adrenal gland secretion of corticosterone stress hormones.
- Cool Water Supply: Flush water lines frequently to keep drinking water below 24°C (75°F). Warm water (> 30°C) is rejected by birds, worsening dehydration.
5. Frequently Asked Questions (FAQ)
Q: What are the first signs of heat stress in chickens?
Early signs include rapid panting (gasping with open beak), spreading wings away from the body to release trapped heat, reduced feed intake, increased water drinking, and lethargy.
Q: What electrolytes help chickens during hot summer weather?
Adding sodium bicarbonate (baking soda), potassium chloride, Vitamin C, and commercial electrolyte powders to drinking water helps restore blood electrolyte balance disrupted by excessive panting.