ISSUE FOCUS 36 FEED & ADDITIVE MAGAZINE July 2024 of air. One can consider it as the amount of energy stored in the air. The more energy stored in the air, the less energy an organism can transfer to the air for thermoregulation. A range of multifaceted and complex functional mechanisms are triggered by thermal stress. These mechanisms are aimed at maintaining or restoring balance and allowing the birds to cope with a challenging environment. Some of these key mechanisms include: • Heat dissipation • Respiration changes • Blood flow regulation • Electrolyte balance • Hormonal responses • Heat shock protein upregulation • Behavioral adjustments OUT IN THE COLD Low ambient temperatures typically cause cold stress in poultry, requiring the bird to expend energy that would otherwise be used to maintain health and productivity. As such, cold stress can have negative effects on the antioxidant, immune, and neuroendocrine systems, and can even lead to death. Birds experiencing cold stress may have increased feed intake to meet caloric needs for thermoregulation, but reduced weight gain and feed efficiency. However, if it is very cold, birds may reduce their feed and water intake as they minimize movement. Cold stressed poultry often have decreased growth rates, reduced egg production, and an increased susceptibility to health problems such as respiratory problems. Poultry under cold stress exhibit several observable behaviors that are closely related to energy conservation, such as huddling, fluffing feathers to trap warm air, shivering, and seeking shelter (Figure 1). TOO HOT TO HANDLE Poultry’s naturally high body temperatures make heat stress more challenging to manage than cold stress. Poultry do not sweat and primarily regulate their body temperature by panting. This means that when both ambient temperature and humidity increase, natural cooling mechanisms become ineffective, which can lead to heat stress. The level of discomfort the bird is thought to experience can be estimated with a Temperature-Humidity Index. The higher the number, the greater the discomfort the animal is thought to experience and the more critical measures are needed to support the animal (Figure 2.) Heat stressed poultry need to dissipate excess body heat and will exhibit certain behaviors to indicate that they are overheated. Poultry will exhibit increased panting as the most common sign. Birds experiencing heat • Excessive panting • Spreading wings to increase airflow • Increased restlessness • Reduced social interactions • Increased aggression and pecking • Changes in nesting or roosting behavior • Excessive dust bathing • Crowding around water sources • Increased water intake • Decreased feed intake • Decreased productivity • Lethargy HEAT STRESS COLD STRESS • Pale comb and wattle • Increased feed intake • Decreased productivity • Huddling together to keep warm • Shivering • Seeking shelter • Fluffed feathers to trap warm air • Reduced activity • Lethargy Figure 1. Signs that your birds are thermally stressed
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