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Heat stress in poultry: Physiological effects, risks and management

Heat stress is one of the most critical challenges faced by poultry producers. With rising global temperatures, the poultry industry experiences a ripple effect. High environmental heat not only compromises bird welfare and increases mortality but also reduces productivity, ultimately impacting farm profitability. The thermoneutral zone for poultry birds is 18–22°C, within which birds can maintain their body temperature without expending extra energy, supporting both comfort and performance. Beyond this range, thermoregulation becomes increasingly challenging. Heat dissipation becomes difficult because birds lack sweat glands and rely only on panting. As panting increases, more energy is diverted away from metabolism and essential body functions. In modern fast-growing broilers, increased body weight further reduces the surface-area-to-volume ratio, making heat loss even more difficult and increasing vulnerability to heat stress. Humidity intensifies heat stress Humidity, along with heat, intensifies the situation. A general principle is that for every 10% increase in humidity, the perceived heat level of poultry increases by approximately 2°C. Thermosensitivity index calculators help estimate the “perceived temperature” that poultry actually experience. For example, at 34°C and 40% humidity, the perceived temperature is approximately 35°C. However, if humidity increases to 65%, the thermosensitivity index can skyrocket to 44°C, significantly increasing the risk of mortality. This synergistic effect accelerates dehydration, electrolyte imbalance and cardiovascular strain, while also increasing oxidative stress and inflammation in internal organs. The combined effects of heat and humidity thus amplify physiological disruption, making it harder for birds to maintain homeostasis under challenging environmental conditions. Physiological effects of heat stress Heat stress is one of the most significant environmental challenges limiting poultry performance, affecting physiology long before visible symptoms appear. Thermoregulatory breakdown When ambient temperature exceeds the thermoneutral zone, birds increase panting and peripheral blood circulation to dissipate heat. Over time, this leads to respiratory alkalosis, electrolyte imbalance and increased energy expenditure for cooling, leaving less energy for growth and egg production. Blood is diverted from the gut and internal organs to the skin, reducing nutrient and oxygen supply, thereby impairing digestion and absorption. Hormonal stress activation Heat stress activates the hypothalamic–pituitary–adrenal (HPA) axis, resulting in elevated corticosterone levels. Chronically elevated corticosterone suppresses protein synthesis, reduces feed intake, and shifts energy allocation toward basic survival functions instead of production. This hormonal shift also weakens immune responses, increasing susceptibility to infection. Gut integrity and barrier breakdown Oxidative stress damages intestinal cells, tight junction proteins and villi, reducing the absorptive surface area. Studies indicate reduced villus length in the duodenum and jejunum, along with lower relative intestinal weight in heat-stressed birds, impairing nutrient digestion and uptake. Compromised gut integrity increases intestinal permeability, allowing luminal contents, including bacterial lipopolysaccharides (LPS), to translocate into circulation (“leaky gut”), promoting systemic inflammation and dysbiosis. This also favours the growth of pathogenic bacteria such as Salmonella and Campylobacter, raising the risk of enteric disease and secondary infections. Immune suppression and systemic inflammation Heat‑stressed birds often display suppressed lymphocyte activity, altered cytokine profiles and reduced immune responsiveness. At the same time, translocated LPS activates inflammatory pathways via receptors such as toll‑like receptor 4 (TLR4), elevating inflammatory markers and further taxing the animal’s energy reserves. The combination of immune suppression and chronic inflammation increases disease susceptibility, dependence on therapeutic interventions and mortality. Key symptoms of heat stress in poultry Increased panting Wing spreading to dissipate heat Seeking shaded or well-ventilated areas Swollen, reddened combs and wattles Reduced activity level Decreased feed intake and increased water consumption. Figure 1 - Relative Humidity Index Impact of heat stress on poultry production Impact on broilers Heat stress in broilers significantly reduces feed intake and nutrient absorption, diverting energy from muscle growth to thermoregulation. This results in poor weight gain, higher feed conversion ratios and increased mortality (see Figure 1). Carcass quality is also compromised, with a higher incidence of pale, soft, exudative (PSE) meat, reduced water-holding capacity and increased processing losses. Chronic exposure further weakens immunity, heightening vulnerability to infections and overall performance losses. Impact on layers Layers show a decline in egg production and shell quality under heat stress. Excessive panting leads to CO₂ loss, triggering respiratory alkalosis, which reduces carbonic anhydrase activity. This limits calcium and carbonate transfer to the shell gland, resulting in thin, fragile shells that cannot be corrected solely by dietary calcium supplementation. Reduced feed intake and phosphorus loss further impair calcium availability, reducing shell strength. Impact on breeders In breeder flocks, heat stress reduces reproductive efficiency, including fertility, sperm viability and hatchability. Immunosuppression further increases disease susceptibility, negatively affecting overall flock performance. Strategies to mitigate heat stress Effective heat stress management requires an integrated approach combining environmental control and nutritional strategies. Optimise ventilation and reduce stocking density Lower light intensity and minimise bird disturbance during peak heat hours Use cooling systems such as foggers, sprinklers and roof insulation or whitewashing Ensure continuous access to clean, cool drinking water Flush water lines regularly and insulate pipelines from heat exposure Adjust feeding schedules to cooler periods (early morning and evening) Enhance diet formulation by increasing nutrient density and using highly digestible ingredients. Managing stress from within: The role of Phytocee While external interventions are essential, they often reach their limits, especially under high humidity. This is where internal resilience becomes critical. Phytocee, formulated by Natural Remedies Pvt. Ltd, works as a natural defence enhancer by enhancing endurance, optimising CMI and helping to reduce the harmful effects of stress. Phytocee is designed to support the bird from within by addressing key stress pathways. By improving the bird’s ability to cope at the cellular and systemic level, Phytocee complements environmental and nutritional strategies, creating a more robust defence against heat-humidity stress. Building resilience Heat stress under high humidity is no longer an occasional challenge but a defining factor in modern poultry production. Its impact extends beyond immediate performance losses, affecting long-term health, reproductive efficiency and overall sustainability. With increasing global warming, the question is no longer how to eliminate heat stress, but how we can help birds withstand it effectively. Solutions such as Phytocee represent an important step in this direction, shifting the focus from reactive management to proactive resilience. In the end, the success of poultry production in a warming, more humid world will depend on how well we understand and support the biology of the bird, both outside and within.To find out more about the product, reach out: [email protected].

By Natural Remedies & Dr Divya Divakaran