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. Thus, it is key to measure both the temperature and humidity in the barn.

Temperature
The thermoneutral zone is the range of environmental temperatures in which an organism can maintain its body temperature. For most poultry, the thermoneutral zone is between 60 and 75 F. This zone represents the temperature range where heat production is lowest. As temperatures increase towards 85 F, the birds adjust their behavior and decrease feed intake and production. These changes help prevent the bird’s core body temperature from rising.

When air temperature increases towards 100 F, 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 F with humidity above 50 percent place them in the danger zone. At 90 F and 50 percent humidity, the risk increases to extreme.

If misting or fogging at low humidity’s, monitor relative humidity to prevent excess moisture in the air that can worsen heat stress conditions.

Keeping Birds Cool

Providing ventilation
In most cases, you can manage heat in
your flock through the airflow. Airflow at the birds’ level is key to removing bird heat. Increasing ventilation to remove heat from the birds should be your 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 feed during nighttime hours when we expect cooler temperatures to occur. Have the feeders full when lowering the feedline. 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. Thus, only follow this feeding method when you expect heat stress temperatures.

Managing water
During heat stress, birds will increase their water intake by 2 to 4 times their normal intake. 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.

Using electrolytes
You can add electrolytes to your flock’s drinking water for up to three days. Heat stress causes increased loss of several minerals, including potassium, sodium, phosphorus, magnesium, and zinc. Potassium chloride electrolytes appear to increase water intake when provided in drinking water at 0.6 percent concentration. It has been generally more effective than other potassium and sodium salts.

You should start providing electrolytes before the heat stress period.

Providing 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. Thus, sodium bicarbonate can help lessen these changes.

Supplementing 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.

Signs of heat stress
As air temperatures increase towards 85 degrees, the bird will try to lose heat through evaporative cooling and 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.

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.