Heat stress calculator for broiler chickens
This calculator estimates heat stress in market-size broiler chickens from the air temperature, the relative humidity and the air speed at bird level, using the temperature-humidity-velocity index published by Tao and Xin in 2003. It shows the index and the stress state the study links to it after 90 and 120 minutes.
Fill in temperature, humidity and air speed to see the result.
Relative humidity must be between 5% and 99%.
- Stress state after 90 minutes
- After 120 minutes
- Temperature-humidity-velocity index
- Wet bulb temperature
How the number is worked out
- The wet bulb temperature is worked out from the air temperature and the relative humidity with the Stull (2011) equation, which assumes sea-level air pressure.
- The index is 0.85 times the air temperature plus 0.15 times the wet bulb temperature, in °C, multiplied by the air speed in m/s raised to the power -0.058.
- Faster air lowers the index, which is the cooling effect of tunnel ventilation expressed as a number.
- The state is read from the thresholds the study published for 90 and 120 minute exposures. Each figure is taken as the upper limit of its state.
The four states in the study
| State | Index after 90 minutes | Index after 120 minutes |
|---|---|---|
| Normal | 35°C | 34°C |
| Alert | 38°C | 37°C |
| Danger | 40°C | 38°C |
| Emergency | > 40°C | > 38°C |
The study defined the states by the rise in the birds' core body temperature: up to 1.0°C normal, 2.5°C alert, 4.0°C danger, more than 4.0°C emergency. Values are approximate, as published.
Sources
- Tao, X. and Xin, H. (2003). Acute synergistic effects of air temperature, humidity, and velocity on homeostasis of market-size broilers. Transactions of the ASAE 46(2): 491-497. The study used male broilers aged 46 ± 3 days and weighing 2.8 kg.
- Stull, R. (2011). Wet-bulb temperature from relative humidity and air temperature. Journal of Applied Meteorology and Climatology 50: 2267-2269.
Watch the inputs all day
Henlytics measures temperature and humidity in the house continuously and alerts your phone when a reading leaves the range you set, so a hot afternoon is caught while it builds.
Poultry house air monitoringQuestions farmers ask
What is a heat stress index for broilers?
A single number that combines the conditions that load heat on the bird. The index used here, from Tao and Xin (2003), combines air temperature, humidity through the wet bulb temperature, and air speed, and was built from the rise in core body temperature of market-size broilers exposed to hot conditions.
Why does air speed change the result?
Moving air carries heat away from the bird. In the index the air speed divides the temperature term, so the same temperature and humidity give a lower index in a tunnel-ventilated house with fast air at bird level than in still air.
Can I use it for young broilers or laying hens?
The index was developed on market-size male broilers aged 46 ± 3 days and weighing 2.8 kg, so the thresholds apply to birds like those. For other ages and bird types, use the temperature guidance in your breed management guide.
Know when the house gets hot, not after
Tell us how many houses you run. We will propose the temperature and humidity points for each house and send a quote.