In poultry, heat stress occurs when an imbalance exists between the heat that is produced by the body and the heat that is dissipated from the body. Environmental temperatures warmer than 80.6 degrees F typically cause chickens to start to experience heat stress. Heat stress can be labeled three different ways: acute heat stress, moderate heat stress and chronic heat stress.
Acute heat stress lasts from one to 24 hours, moderate heat stress lasts around seven days and chronic heat stress lasts seven days or longer. These distinctions are important because birds are more likely to experience detrimental effects from heat stress the longer it goes on. Identifying specific heat stress behaviors within the flock is key so action can be taken quickly to minimize the potential damage.
How Birds Adapt
Unlike humans, birds don’t have sweat glands. Instead, they dissipate heat through certain behavioral and physiological strategies. Panting, for example, allows the bird to transfer heat through respiratory evaporation. For this reason, one of the first heat stress indicators is panting.
Birds also dissipate heat by pumping blood to the peripheral vascularized areas of the body like the skin, wattle and comb and reducing blood flow to other organs such as the intestinal tract. Keep an eye on their combs and wattles. Those parts of a bird’s body tend to be a brighter shade of red when temperatures soar.
Reducing a chicken’s core body temperature is another mechanism poultry use to try to combat heat stress. Birds attempt to bring their body temperatures down by decreasing feed intake and increasing water intake. Reducing the amount of feed consumed allows for less metabolic heat to be produced, while drinking more water helps to replenish water lost through panting.
Normally birds drink about twice as much as they eat. However, when chickens experience heat stress, they drink five times as much! These physiological and behavioral changes help ensure birds’ survival in extreme heat.
You may also observe your birds performing certain behaviors when they are heat stressed, such as wing spreading and squatting along with reduced activity. Wing spreading is when a bird holds their wings away from their body to expose the areas that do not have any feathers. Doing this helps to dissipate body heat, especially when there is air movement.
Squatting is when birds place their body in contact with the ground to increase heat conduction. Observing these behaviors within your flock is an accurate indicator of heat stress. 
Heat Effects
The physiological and behavioral changes that happen during heat stress can have a negative effect on health and production. As mentioned previously, heat-stressed birds dissipate heat by opening blood vessels in tissues such as the skin, wattle and comb and vasoconstricting blood from the intestinal tract. This limits the integrity of the intestinal tract and its function, as heat stress has been shown to reduce intestinal cells’ ability to absorb glucose.
When this happens, less energy is being utilized by our birds and more nutrients are available for bad bacteria. Plus, the decrease in intestinal integrity means bacteria can move more easily from the gut into our birds’ bodies. Heat stress has also been shown to cause inflammation and oxidative stress, which can cause tissue damage in chickens.
These factors have a negative effect on performance and can lead to other types of challenges, such as summer molts or potential diseases.
Heat stress also affects egg production and egg quality. Moderate and chronic heat stress causes excessive panting, which can decrease calcium and carbon dioxide pressure in the blood, thus increasing the blood’s pH. This change in blood chemistry can have a direct effect on bone strength and function as well as eggshell quality.
The primary reason hens produce fewer eggs during hot temperatures is because they’re eating less feed. However, heat stress also disrupts the hormones responsible for egg laying. Plus, the reduction in blood calcium reduces eggshell quality. These factors are some of the reasons we see fewer eggs in the summer.
Preventative Measures
As backyard chicken-keepers, we can help reduce the negative effects of heat stress through certain nutritional and management strategies. Chickens eat less during high temperatures to reduce metabolic heat. To accommodate the decrease in feed intake, we can improve the quality of the feed. We can also provide a meal mixer that contains a higher amount of fats, quality protein and amino acids to support egg production and gut health.
Offering a pelleted diet has also been shown to help maintain egg production during the summer months.
Other nutritional strategies include providing electrolytes, additional vitamins and minerals, and probiotics. Electrolytes help reduce the blood chemistry imbalances caused by panting, encourage water consumption and help increase tolerance to heat stress while supporting eggshell quality.
Supplementing vitamins and minerals can also play a role in reducing the negative effects of heat stress by helping to reduce the antioxidant mechanisms that support nutrient transports. During heat stress, when birds are drinking a lot more than they are eating, adding these nutrients to water is a great way to support our chickens. Probiotics can also help reduce the negative effects of heat stress by alleviating oxidative stress and supporting gut morphology, integrity and nutrient utilization.
To support your flock with nutritional changes, feed a high-quality diet, feed a pelleted feed and supplement with probiotics, vitamins and minerals, and electrolytes to avoid some of the negative effects of heat stress in the summer months.
Management strategies play a big role in combatting heat stress for our flocks, too! Providing shelter and shaded areas, cooling fans, ventilation and sprinklers during hot summer months are highly beneficial, especially during extreme heat stress when squatting and wing spreading are observed.
Heat stress can have serious consequences on the health and welfare of our chickens, especially if heat stress is chronic. By understanding how our poultry express signs of heat stress through their behaviors and physiology, we can intervene as soon as possible to help minimize the damage.
By implementing beneficial nutritional strategies such as adding supplements to the water and management strategies such as ventilating the coop, we can help ensure our birds beat the heat this summer.
This article originally appeared in the July/August 2023 issue of Chickens magazine.
