Heat stress in poultry farming: how to protect your birds this summer

August is, every year, the most dangerous month on any poultry farm. Heatwaves don’t just make birds uncomfortable: they can trigger heat stress within minutes and cause drops in egg-laying, poorer egg quality or mortality in the flock. Understanding why it happens and what can be done, both in terms of management and nutrition, makes the difference between a difficult season and a productive crisis that puts the animal’s life at risk.

What is heat stress and why are birds so vulnerable?

Heat stress — also known as thermal shock — occurs when the bird can no longer dissipate the heat it receives from the environment plus the heat generated by its own metabolism. As a result, its body temperature rises above what its organism can tolerate. As a reference, laying hens are comfortable within a thermoneutral zone of between 19 and 22 °C, and broilers between 18 and 22 °C; above that range, the bird has to actively work to regulate its temperature.

Unlike other livestock species, birds have no sweat glands, so they cannot cool down by sweating. Their plumage also acts as insulation that hinders heat loss through the skin. They have only two real resources: on one hand, directing more blood flow towards featherless areas — comb, wattles and legs — to radiate heat into the environment, and on the other, panting, meaning opening the beak and speeding up breathing to lose heat through evaporation in the respiratory tract.

This is where the paradox that makes heat stress so dangerous appears: panting itself, since it involves constant respiratory and muscular effort, generates additional metabolic heat. The bird, in its attempt to cool down, produces more heat than it manages to eliminate. In addition, this sustained panting causes hyperventilation that reduces blood CO2 levels and disrupts the acid-base balance, leading to respiratory alkalosis. This imbalance not only weakens the animal, but also reduces the availability of calcium carbonate that the hen needs to form the eggshell, which explains why thinner, more fragile eggshells appear during heatwaves.

On top of this comes oxidative stress: science describes how acute heat stress triggers the production of free radicals and damages the bird’s antioxidant balance, which explains why the impact isn’t just about “feeling hot” — it’s real, cumulative physiological wear that reduces the bird’s ability to respond to other health challenges.

Broilers and laying hens: different heat, different birds

Although the underlying mechanism is the same, the consequences change depending on the production orientation and physiology of each type of bird:

• Broilers: their genetic selection for rapid growth means a very high breast muscle mass relative to their body surface area, which reduces the proportion of skin available to dissipate heat compared to the volume of tissue generating it. The closer they get to slaughter weight, the worse their surface-to-volume ratio for losing heat. In addition, heat compromises the intestinal barrier and antioxidant status: research in broilers has shown that heat stress alters the gut microbiota and reduces mucosal integrity, resulting in poorer feed conversion and lower weight gain (DOI: 10.1016/j.psj.2022.102408).
• Laying hens: in their case, the impact is mainly reproductive and hormonal. A study with Hy-Line Brown hens exposed to temperatures of 35-37 °C showed that heat triggers apoptosis (programmed cell death) in ovarian follicle cells and alters the ratio between estradiol and progesterone; as a result, the number of available follicles decreases and egg production drops as early as the third day of heat exposure (DOI: 10.1016/j.psj.2020.07.024). Another study using an elevated temperature-humidity index (THI) recorded drops of up to 30% in feed intake and 11% in egg production, along with thinner shells and poorer internal quality (DOI: 10.3390/ani14071076).

In short: the broiler mainly suffers from an “excessive engine, too little bodywork” problem when it comes to losing heat, while in laying hens heat stress directly affects the reproductive axis and eggshell quality. See also why gut health matters in poultry farming to understand how to protect it year-round, beyond heat episodes.

How to spot the symptoms of heat stress in time?

Recognising the signs early is the best defence. Watch out for:

• Intense, sustained panting, with the beak constantly open.
• Wings held away from the body, trying to lose heat through areas with less plumage.
• Listless birds, with plumage pressed against the body and little activity.
• Lower feed intake, while water consumption rises noticeably.
• In the most severe cases, trembling, erratic movements or loss of consciousness.

If you observe several of these signs in the same flock, it’s time to act without delay: every hour of exposure without correcting the situation increases the risk of mortality.

Environmental management: the first line of defence

Before thinking about nutrition, you need to make sure the house offers the minimum conditions for the bird to dissipate excess heat, especially during August heatwaves:

• Effective ventilation: generating airflow inside the house reduces the actual heat sensation, not just the thermometer reading.

• Shade and insulation: avoiding direct solar radiation on roofs and walls helps keep the indoor temperature from spiking.
• Fresh, abundant water: check that all drinkers are working and that the water doesn’t overheat; water intake is the bird’s first way of compensating.
• Reducing density where possible: fewer birds per square metre means less accumulated metabolic heat across the house.

• Adjusting management schedules: concentrating tasks and feed supply during the coolest hours of the day reduces added stress.

The role of nutrition against heat stress

Environmental management is the foundation, but nutrition is the tool that lets you act on each physiological front: fluid and electrolyte loss, oxidative stress, damage to the gut mucosa and wear on the immune system. Protecting your birds’ welfare during a heatwave means taking preventive measures on several fronts at once:

• Electrolytes: the bird loses mineral salts through increased panting and water intake; replenishing sodium, potassium, chloride and bicarbonate helps maintain fluid balance, supports hydration and prevents dehydration, which is the main cause of losses associated with heat stress. Proper rehydration also helps correct part of the acid-base imbalance caused by respiratory alkalosis.
• Antioxidants: compounds such as selenium have been shown to improve feed intake, weight gain and immune response in birds exposed to high temperatures (DOI: 10.1007/s12011-015-0275-x). Other antioxidants such as vitamin E, combined with flavonoids like quercetin, have also been shown to specifically improve oviduct function, calcium metabolism and eggshell quality in heat-stressed hens (DOI: 10.3390/ani14111554).
• Gut health support: heat damages the integrity of the gut mucosa and increases its permeability, making it easier for bacteria and toxins to pass into the bloodstream. Providing nutrients and additives that support the repair of that barrier — and that sustain a balanced gut microbiota — helps the bird keep making the most of the feed it consumes even during a heatwave. Research in broilers backs this approach, showing that supplements such as glycine protect the gut barrier damaged by heat (DOI: 10.1016/j.psj.2022.102408).
• Probiotics and phytobiotics: several studies in older laying hens show improvements in egg production and gut health when specific probiotics are added during heat episodes (DOI: 10.1016/j.psj.2026.107039).

Within the AMBiotec range there are several supplements that fit into this comprehensive strategy. For the gut tract, RFN WS is a yeast-based probiotic that provides, together with the yeasts themselves, all the metabolites derived from their fermentation, supporting a more balanced gut ecosystem right when the mucosa is most compromised by heat. Finally, as an additional supplement for general digestive health during these periods, phytobiotic products such as Cocci Cero are designed to modulate the gut microbiota and protect the digestive mucosa while birds keep feeding on their normal diet.

The combination of these products and the dosage should be adjusted based on the flock’s condition and production stage, but always with the goal of preventing issues and maintaining animal health and welfare.

Conclusion: preventing heat stress before it arrives

Heat stress in poultry farming isn’t simply “feeling hot”: it’s a physiological cascade that runs from panting to respiratory alkalosis, from oxidative stress to hormonal decline, ultimately resulting in fewer eggs, poorer quality and higher mortality. Understanding this mechanism, telling apart how it affects broilers and laying hens, and combining environmental management with appropriate nutritional support is what turns a heatwave into a controlled setback instead of a productive crisis.

Heat stress isn’t solved the day the first symptoms appear: it’s prevented weeks in advance, by checking ventilation, drinkers and nutritional programmes. Getting ahead of August heatwaves is, ultimately, the most effective way to protect both animal welfare and farm results. See also how heat stress affects other livestock species such as pigs and cattle.

Frequently asked questions

What first aid should I provide in individual cases?

Move the bird to the coolest, best-ventilated area available and give it immediate access to fresh water, without forcing it to drink. Improve ventilation in the environment as soon as possible. Avoid submerging it in very cold water, as too abrupt a cooling can cause more physiological stress rather than relieving it. If it doesn’t recover within a few minutes, contact a veterinarian.

Are fewer resources allocated to the egg to preserve the mother’s integrity during heat stress in laying hens?

Yes, and not only through the ovarian pathway already discussed. Heat stress also directly impairs oviduct function: it reduces blood oestrogen and progesterone levels and compromises calcium metabolism at the shell gland, affecting shell thickness and strength. At the same time, panting itself generates respiratory alkalosis, which reduces the carbonate available to that same gland. The combined result is that the body prioritises its vital functions over egg quality and quantity, even when the hen keeps laying at a relatively normal rate.

Can feather pecking also be a sign of heat stress?

It isn’t a direct or classic symptom of heat stress, but it can be related. Feather pecking mainly stems from redirected foraging behaviour and serotonin imbalances, but it shares an underlying physiological pathway with heat stress: activation of the hypothalamic-pituitary-adrenal axis and the release of corticosterone. That’s why, in flocks already under heat stress, it’s more likely to also observe episodes of feather pecking as an added manifestation of the animal’s general stress.