Chickens are particularly sensitive to hot, humid weather conditions and are at risk of heatstroke. Because chickens have high body temperatures and lack sweat glands, they rely on panting to release heat from their bodies. Without heat regulation, birds often suffer from heatstroke and its complications.
One of the reasons for poor growth performance in poultry has been attributed to heat stress, which impairs immune and intestinal functions, causes endocrine dysfunction, and increases oxidative stress. The hypothalamic axis is stimulated by heat stress due to increased levels of adiponectin and leptin, resulting in reduced feed intake. Animals under heat stress can reduce heat production by minimizing feed intake. Recent studies have shown that heat stress complications are less common in animals fed a high-protein diet than in those fed a high-energy, high-fat diet.
When does heat stress occur?
Heat stress occurs when a bird’s core body temperature rises to a lethal temperature due to reduced heat loss. Both ambient temperature and humidity play a role in heat stress, so it is essential to measure both in the breeding house.
Heat stress is a threat that can lead to significant financial losses to poultry production in tropical and arid regions of the world. The degree of heat stress (mild, moderate, severe) experienced by poultry depends largely on thermal radiation, humidity, the animal’s ability to regulate body temperature, metabolic rate, age, severity, and duration of heat stress.
Today’s commercial broilers have a fast metabolism that causes them to produce more heat and are susceptible to heat stress. The negative impact of heat stress on the physiology, health, production and behavior of poultry birds is reviewed in this article.
Interestingly, each of these strategies finds application at different stages of the poultry life cycle. For example, gene mapping before breeding and genetic selection during breeding are promising tools for developing heat-tolerant breeds. Thermal conditions during embryonic or early life development enhance the birds’ ability to tolerate heat during adult life.
Nutritional management such as dietary manipulation, night feeding and wet feeding, often combined with timely and effective modification of environmental conditions, has been shown to ameliorate the impact of heat stress in chicks and adult birds. As long as climate crises persist, heat stress may continue to require significant attention. Therefore, it is essential to review current trends.
Temperature
The neutral thermal zone is the temperature that is comfortable for a bird. The neutral thermal zone is the range of ambient temperatures in which an organism can maintain its body temperature. For most birds, this zone is between 60 and 75 degrees Fahrenheit (16 and 24 degrees Celsius) and represents the temperature range in which heat production is minimal.
As temperatures rise toward 85 degrees Fahrenheit (30 degrees Celsius), birds adjust their behavior and reduce feed intake and production. These changes help prevent the bird’s core body temperature from rising. When temperatures rise toward 100 degrees Fahrenheit (37.8 degrees Celsius), birds’ core body temperatures rise to a lethal temperature unless help is provided.
Humidity
High humidity reduces heat dissipation from poultry lungs, making birds more susceptible to heat stress. For older turkeys, temperatures above 85 degrees Fahrenheit with humidity above 50 percent put them in the danger zone. At 90 degrees Fahrenheit and 50 percent humidity, the risk increases dramatically.
(If misting in low humidity, control the relative humidity to avoid excess moisture in the air, which can worsen heat stress conditions.)
How to keep birds cool
ventilation
In most cases, you can manage the heat in your flock through airflow. Airflow is key for birds to dissipate body heat. Increasing ventilation to reduce body heat in birds should be your first priority.
Feeding
Birds are usually hungrier in the morning and tend to overeat, making them more susceptible to heat stress in the afternoon. Stopping feeding six hours before peak temperatures in the afternoon can reduce the risk of heat stress. You can feed them again after the temperature starts to drop (after the peak temperature). The birds can then feed during the night hours, when we expect cooler temperatures. You can use lighting during night feeding (midnight) to increase food intake.
Depending on how often you use this feeding method, you may notice weight loss. Only use this feeding method when you expect high temperatures that could lead to heat stress.
Water
During heat stress, birds increase their water intake by 2 to 4 times their usual amount.
Adequate space for active drinkers and cool water temperatures will encourage birds to drink. Clean water pipes and drinkers regularly to keep the water fresh and cool.
Electrolytes
Heat stress increases the loss of several minerals, including potassium, sodium, phosphorus, magnesium, and zinc. You can add electrolytes to your herd’s drinking water for up to three days.
Potassium chloride electrolytes, provided at a concentration of 0.6% in drinking water, appear to increase water intake. They have generally been more effective than other potassium and sodium salts. You should begin providing electrolytes before the heat stress period.
Sodium bicarbonate
Sodium bicarbonate in feed or water (especially for chickens) is beneficial for egg production. Panting and the release of carbon dioxide can alter the acid-base balance in poultry and the bicarbonate available for eggshell formation. Sodium bicarbonate can help reduce these changes.
Vitamins
Fortifying drinking water with vitamins can significantly prevent heat stress in broilers. In poultry farming, adding vitamins and enzymes can effectively modulate the reduction in egg production and eggshell quality in laying hens and sperm production in roosters at high temperatures.
Other measures
– Delay activities inside the poultry house, such as moving birds or preparing litter.
– Provide shade for poultry in the pasture or reduce the amount of sunlight in the area
– Always provide fresh, cool, clean water for the flock: Place drinkers in the shade, add ice, refill with cool water, and check them regularly. Provide multiple shaded areas: There should be enough shaded areas throughout the day so that each member of the flock can stay out of the sun.
– Ensure proper ventilation: Chickens in poorly ventilated areas are at greater risk of heat stress because it blocks airflow. Maintain airflow: Install fans and/or position the chicken coop to maximize exposure to wind and good airflow. On the other hand, eliminate things that might block airflow, such as pruning shrubs and trees or moving other structures to another area.
Clinical signs
Panting, lethargy, increased thirst, decreased egg production, raised wings, decreased feed intake, weakness, watery stools…
Solutions
Overall, a multi-pronged strategy for heat stress management should be adopted in the poultry industry. Future trends in the poultry industry should be prepared to change the way heat stress is handled in poultry. Precise climate control, using advanced sensors and automated systems to actively regulate temperature, humidity, and ventilation in poultry houses, should take center stage as ambient temperatures rise.
Targeted breeding techniques are needed to produce heat-tolerant breeds as a result of genetic advances, and specialized diets and nutrient-rich food supplements that regulate body temperature are vital tools to increase birds’ resistance to heat stress.
Innovative cooling techniques such as evaporative cooling and radiant surfaces should also be explored. In addition, there should be a focus on behavioral monitoring using AI-based sensors to detect heat stress and the use of relevant algorithms to predict heat stress and enable rapid responses.
Genetic selection of heat-tolerant breeds in poultry, precise climate control systems, innovative cooling methods, and specialized nutritional interventions also need to be carefully tailored to reduce the impact of thermal challenges on poultry production.
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