Stress is a biological adaptive response to restore homeostasis, and occurs in every animal production system, due to the multitude of stressors present in every farm. Heat stress is one of the most common environmental challenges to poultry worldwide, potentially triggered by a variety of conditions, such as regional climatic conditions, failure of ventilation and temperature controls (manual or automatic systems), inadequate brooding conditions, and high stocking density, particularly at the end of the finisher phase. It is well-known that heat stress negatively impacts the health, welfare, and productivity of poultry, and therefore, understanding and controlling environmental conditions are crucial to successful poultry production.
Poultry (broilers, turkeys, layers, etc.) are endothermic homeotherm animals, which are animals that keep their body temperature within a relatively narrow range over a wide range of environmental conditions by balancing heat production and heat loss. When birds are subjected to conditions leading to heat stress, behavioral and physiological changes or adaptations occur seeking thermoregulation to restore homeostasis. However, there are individual variations in intensity and duration of heat stress response within the same population or flock. This consideration is very important in cases of mild-moderate heat stress conditions in the field, as it poses a challenge for producers to identify and correct environmental conditions and minimize negative effects quickly.
Under heat stress conditions, birds will increase the use of their air sacs to promote air circulation on body surfaces to increase gas exchanges with the air, and consequently, loss of heat. This is known as panting, which consists of frequent, short, quick breathing. In addition to panting, birds subjected to heat stress conditions will spend less time feeding and more time drinking, as well as more time with their wings elevated, less time moving or walking, and more time inactive. From a practical point of view, under commercial production conditions, it is very important to closely monitor water and feed consumption during periods of higher heat stress risk. Rapid increase in water and decrease in feed intake can be good indicators of flocks being subjected to heat stress conditions.
A cardiovascular adaptive response takes place in animals under heat stress conditions, which consists of increasing blood flow to the external surface of the body (skin) in attempt to promote heat loss and reduce heat gain from the surrounding environment. However, a compensatory reduced blood flow to internal organs occurs as a mechanism to maintain overall blood pressure stable. Consequently, there is reduced availability of oxygen, energy and nutrients to the intestinal mucosa negatively impacting the intestinal barrier integrity and permeability. This is aggravated by the reduced feed intake, ultimately resulting in oxidative stress and inflammation along the intestinal tract. Obviously, depending on the magnitude of these alterations, the health and productivity of the flock will be significantly affected.
Due to the complexity of the heat stress challenge, as well as of the adaptive response developed by the birds, producers must adopt a multi-pronged approach, paying close attention to the following key points:
- Closely monitor weather forecast (particularly, during the warm season) for potential heatwaves, which will require a higher level of attention and preparation, such as additional visits to flocks focusing on the key points listed below.
- Maintain good environmental management practices, paying close attention to the ventilation conditions in all areas inside the house.
- Train staff very well, not only on environmental management practices, but also to watch closely and quickly identify animal behaviors indicative of discomfort.
- Closely monitor water intake and quality, which should always be fresh, clean and cool.
- Closely monitor feeding behavior (frequency of birds visiting feeders) and feed disappearance.
- Reduce stocking density during the warm season, particularly during the late finishing phase, when birds are larger and require more air circulation to be able to keep thermal balance with the environment.
- Adjust feeding practices accordingly, such as restricting feed during periods of high temperature, and providing it during cooler times of the day, such as early mornings and late evenings/night, when feed intake can be encouraged by leaving lights on during the dark hours.
- Sprinkle or mist the birds with cool water. However, this intervention must be done correctly and in sync with the ventilation to avoid creating excessive environmental humidity, and consequently, further challenges and problems.
Besides these practical interventions, it is important that nutritionists formulate diets according to the metabolic condition of the birds, such as replacing carbohydrates (starch) as an energy source for oil/fat and adjust the energy: protein ratio. Additionally, adjusting feeding practices accordingly can help, such as providing feed during cooler times of the day (e.g., early morning and late evening). If possible, switching from mash/meal to pelleted feed can help to increase nutrient ingestion, during the lower feed intake period. Moreover, nutritionists and veterinarians should discuss and adjust the feed and/or water additives strategy. There are many options available, including antioxidants, vitamins, minerals, probiotics, prebiotics, phytogenics, etc.
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