How Does Heat Stress Affect Egg Production?

barred rock hen in nesting box laying an egg

Baby, it’s hot outside! With soaring summer temperatures in many regions, the effect of heat stress on your hens can be very concerning. We recently wrote about how chickens regulate their body temperature and today we are going to talk about what happens when your hens are stressed by the hot weather.

What is the Ideal Temperature for Laying Hens?

Poultry cannot sweat so they rely on other methods to help regulate their temperature. The internal body temperature of a healthy, adult chicken is about 105ºF. Chickens will use their breath, the surface area of their body, and even their blood to help regulate their body temperature.

Ideal Temperature Zone

The ideal temperature (thermal neutral zone) for an adult laying hen is 64 to 75ºF. In this temperature range, hens do not need to adjust their metabolism to regulate their body temperature. Below this range, hens will need to generate heat to stay warm. Above this range, hens will need to work to release heat from their bodies.

It’s Getting Uncomfortable

Between 75 and 95ºF, hens will use a variety of methods to help release heat from their bodies and maintain homeostasis. In this temperature range, your hens may be uncomfortable but their natural bodily functions – panting, vasodilation, gular flutter, etc. – are usually adequate to deal with this stressor for a short period of time. As poultry keepers, we can help our hens cope by providing plenty of shade, good air flow and ventilation, and plenty of clean, cool water.

The Danger Zone

If the temperature inside a chicken’s living quarters reaches 95ºF, a hen’s ability to cool herself becomes limited and this can quickly result in heat stress. If the ambient temperature meets or exceeds the internal body temperature (105ºF), chickens have no way to cool themselves. This can very quickly lead to an emergency situation for your feathered friends.

What are the Effects of Heat Stress on Egg Production

Once ambient temperature reaches 85ºF, egg production will start to drop. This is usually a direct result of dealing with the effects of heat stress. Any time an animal is stressed, one of the first physiological functions that she will slow or cease is reproduction. Since egg production is reproduction, it makes perfect sense that we can see 15-40% reductions in egg production during periods of heat stress. Egg production may cease all together if hens are dealing with heat stress during sustained heatwaves or periods of very high humidity.

Another common side effect of heat stress is thin eggshells. As a hen pants to dissipate heat, her lungs are producing large amounts of CO2 which has a negative effect on the pH of the bloodstream. Calcium in her bloodstream is then bound to other nutrients due to this pH imbalance. This directly results in less calcium available for eggshell production. This problem can be further exacerbated because feed intake and, thus, calcium intake is usually reduced in hot weather.

What are the Effects of Heat Stress on Water Consumption

The very best way to help your chickens stay cool is lots and lots of fresh cool water. During hot summer weather, you can expect your hens to drink 2.5x more water than they would consume if the temperature were in the ideal range (64 to 75ºF). This water is being used to replace the large volume of moisture a hen loses when she is panting. Water is also required for egg production. A standard Grade A large egg is about 70% water. Your hens need a massive amount of water to maintain proper body temperature and to keep producing eggs!

What are the Effects of Hot or No Water on Egg Production?

Another common culprit that affects egg production in the summer is water quality. Even a short amount of time without potable water can cause a hen to stop laying eggs. Additionally, once the temperature of drinking water exceeds the internal body temperature of the hen (105ºF), she will stop drinking the water because it will heat her body and exacerbate heat stress.

Unfortunately, when a hen is deprived of water for even short periods, the negative effects on egg production can last a long time. Research conducted at Kansas State University in the 1970s showed that hens that go without water for 24-72 hours can take two months to fully recover and return to normal egg production! Even more surprising, it was a full two weeks after the period of water deprivation before egg production reached the lowest level. This means there can be a sustained negative effect on egg production if water is not properly managed during periods of potential heat stress.

Generally, drinking water should be refreshed daily in the summertime and should come from a cool, clean source. Hoses, rain barrels, and water catchment systems that are left in the sun can get very hot. Avoid using water from these sources unless you are absolutely sure the water is cool and clean. Cool, clean water is your best line of defense to help your hens make it through the hottest days of summer!

Keeping poultry is such a wonderful experience and the rewards are many! At Kalmbach Feeds, we are always here to help. If you have any questions about the nutrient needs of your birds, feed options, or general poultry keeping, please let us know. We are so excited to continue writing about all of the topics that are important to you and can’t wait to continue learning about your flocks. Stay tuned and thank you for choosing Kalmbach Feeds!

Have you heard about our Layer Days® Sweepstakes? We are giving away Free Feed for a Year, a prize valued at $1,000 - to two lucky winners.


Nancy Jefferson, Ph.D.

Dr. Nancy Jefferson has been a member of the Nutrition and Technical Services team at Kalmbach Feeds since 2013. She received her Ph.D. from West Virginia University in 2008 and has worked in the feed industry for over 15 years. She lives on a farm in Crown City, OH with her husband, John, and their children. Dr. Jefferson is a passionate poultry enthusiast and loves her chickens! Together, she and her family raise beef cattle and she keeps an ever-growing flock of backyard chickens.