Quick facts
- Birds are subject to heat stress when the air temperature and humidity uncontrollably increase their core body temperature.
- Heat stress can result in panting, increased water intake and eventually death.
- Access to cool, fresh water, ventilation, and adjusted feed schedules can help provide relief to birds.
When does heat stress occur?
Heat stress occurs when the bird’s core body temperature increases to fatal temperatures due to poor heat loss and limited coping means. Environmental temperature and humidity play a role in heat stress, so it is key to measure both in the barn.
Temperature
The thermoneutral zone is the range of environmental temperatures at which an organism can maintain its body temperature. For most poultry, this zone is between 60 and 75 degrees Fahrenheit and represents the temperature range where heat production is lowest.
As temperatures increase towards 85 degrees Fahrenheit, the birds will adjust their behavior and decrease feed intake and production. These changes help prevent the bird’s core body temperature from increasing.
When air temperature increases towards 100 degrees Fahrenheit, the birds’ core body temperatures will increase to lethal temperatures unless relief is provided.
These temperatures can shift depending on humidity, care and building conditions.
Humidity
High humidity decreases poultry heat loss from the lungs, making the birds more prone to heat stress. For older turkeys, temperatures at 85 degrees Fahrenheit with humidity above 50 percent place them in the danger zone. At 90 degrees Fahrenheit and 50 percent humidity, the risk increases to extreme.
If misting or fogging at low humidities, monitor relative humidity to prevent excess moisture in the air that can worsen heat stress conditions.
Signs of heat stress
As air temperatures increase towards 85 degrees Fahrenheit, the bird will try to lose heat through evaporative cooling, panting. Panting creates more heat through muscle activity.
As a result, the bird will increase its water intake, but not enough to keep up with the losses through respiration and urine excretion. Without relief, the changes will worsen, and the bird may die.
How to keep birds cool
Ventilation
In most cases, you can manage heat in your flock through air flow. Airflow at the birds’ level is key to removing bird heat. Increasing ventilation to remove heat from the birds should be your first priority. However, some cases exist where ventilation is limiting.
Naturally ventilated barns are at risk of heat stress if the air is calm and supplemental fans are not present. Mechanically ventilated barns can also be at risk if they lack ventilation capacity and air mixing for the size and number of birds present.
Feeding
Birds are usually hungriest in the morning and tend to fill up, which makes them more prone to heat stress in the afternoon. Withdrawing feed six hours before peak warm temperatures in the afternoon can lower the risk of heat stress.
You can reintroduce the feed after peak temperatures have started to decline. Birds can then feed during nighttime hours when we expect cooler temperatures to occur. You can use lighting during nighttime (midnight) feeding to allow intake.
Depending on how often you use this feeding method, you may notice some body weight loss. Only use this feeding method when you expect heat stress temperatures.
Water
- During heat stress, birds will increase their water intake by 2 to 4 times the normal amount.
- Sufficient water space, operating waterers, and cool water temperatures will encourage the birds to drink.
- Flush water lines and waterers routinely to keep the water fresh and cool.
Electrolytes
Heat stress causes increased loss of several minerals, including potassium, sodium, phosphorus, magnesium and zinc.
- You can add electrolytes to your flock’s drinking water for up to three days.
- Potassium chloride electrolytes, provided in drinking water at a 0.6 percent concentration, appear to increase water intake. They have been generally more effective than other potassium and sodium salts.
- You should start providing electrolytes before the heat stress period.
Sodium bicarbonate
- Sodium bicarbonate in the feed or carbonated water is especially useful for hens in egg production.
- Panting and carbon dioxide release can change the acid-base balance in poultry and the bicarbonate available for eggshell formation.
- Sodium bicarbonate can help lessen these changes.
Vitamins
- Supplementing drinking water with vitamins (A, D, E and B complex) can effectively tackle heat stress mortality in broilers.
- In breeding poultry, vitamin C can effectively moderate warm temperature declines in egg production and eggshell quality in laying hens and sperm production in breeder males.
Other practices
- Delay activity in the barn, such as moving birds or litter conditioning.
- Provide shade for pastured poultry or decrease sun exposure in the barn.
Reviewed in 2026