Dr. Mohini Tripathi1 (MVSc Scholar)
Dr. Shipra Tiwari1 (MVSc Scholar)
Dr. Pawar Rutik Namdev1 (MVSc Scholar)
1Department of Livestock Products Technology, College of Veterinary Science and Animal Husbandry, DUVASU Mathura (281001), India
- Introduction :
Heat stress represents a critical environmental constraint in poultry production, particularly in tropical and subtropical climates. It occurs when ambient temperatures exceed the birds’ thermoneutral range, limiting their capacity to regulate internal body temperature effectively. This thermal imbalance can lead to several physiological disruptions, including decreased feed consumption, metabolic disturbances, oxidative damage, weakened immune function, and electrolyte imbalances. In extreme cases, it may also increase mortality rates. Nutritional management plays an essential role in counteracting the detrimental effects of heat stress. By supporting vital metabolic processes, enhancing heat tolerance, and strengthening overall resilience, targeted nutritional strategies can significantly improve the birds’ ability to cope with elevated temperatures.
2.1. Optimization of Dietary Energy and Protein for Thermal Load Management
Heat stress leads to a significant decline in voluntary feed intake, compromising energy and nutrient availability necessary for growth, maintenance, reproduction, and immune competence in poultry. Targeted adjustments to dietary energy and protein content can reduce endogenous heat production and optimize productivity.
- Enhancement of Energy Density: Increasing dietary energy concentration through the inclusion of high-quality lipid sources (e.g., vegetable oils, animal fats) is recommended. Lipids possess a lower specific dynamic action (SDA) compared to carbohydrates and proteins, thus generating less metabolic heat during digestion and assimilation.
- Reduction of Crude Protein with Balanced Amino Acid Supplementation: Slightly reducing total crude protein helps minimize the heat generated during amino acid deamination and nitrogen excretion, particularly in hot climates. To maintain optimal growth and production, it is essential to supplement limiting amino acids in crystalline form—such as L-lysine, DL-methionine, L-threonine, and L-tryptophan—to ensure amino acid adequacy and reduce nitrogenous waste.
- Use of Highly Digestible Proteins: Incorporating highly bioavailable protein sources (e.g., soybean protein isolates, enzymatically hydrolyzed fish protein) helps reduce digestive workload and supports efficient nutrient utilization while minimizing intestinal fermentation and heat generation.
2.2. Electrolyte Balance and Regulation of Systemic Acid–Base Equilibrium
Heat stress-induced hyperventilation (panting) results in excessive CO₂ expulsion, leading to respiratory alkalosis, which disrupts blood pH homeostasis and reduces systemic buffering capacity. Nutritional strategies must aim to correct this imbalance.
- The Dietary Electrolyte Balance (DEB) is a key parameter in regulating acid–base physiology and is calculated as:
DEB (mEq/kg) = (Na⁺ + K⁺) – Cl⁻
- A DEB range of 250–300 mEq/kg feed is generally optimal for thermally stressed birds.
- Supplementation with sodium bicarbonate (NaHCO₃) aids in buffering excess alkalinity and improving systemic bicarbonate reserves.
- Potassium chloride (KCl) supports intracellular fluid balance and neuromuscular function, while electrolyte-enriched water supplements enhance fluid retention, osmoregulation, and thermotolerance.
Maintaining an optimal electrolyte profile helps prevent dehydration, supports cardiac and muscular function, and enhances overall resilience under heat load.
2.3. Nutritional Antioxidants and Redox Stabilization
Oxidative stress is a hallmark of heat-exposed poultry, with elevated reactive oxygen species (ROS) damaging lipids, proteins, and nucleic acids. Dietary antioxidants are critical for mitigating oxidative stress, preserving tissue integrity, and enhancing immune function.
- Vitamin E (α-tocopherol): A primary lipophilic antioxidant that stabilizes cell membranes and prevents lipid peroxidation.
- Vitamin C (ascorbic acid): A powerful water-soluble antioxidant that also functions as an anti-stress agent by lowering plasma corticosterone levels and supporting adrenal function. Poultry are unable to synthesize vitamin C endogenously, making exogenous supplementation essential during thermal stress.
- Selenium (Se): Acts as a cofactor for glutathione peroxidase (GPx), a critical enzyme in the detoxification of hydrogen peroxide and organic peroxides. Organic selenium forms (e.g., Se-enriched yeast) are preferred for better bioavailability.
- Zinc and Manganese: Integral to the activity of superoxide dismutase (SOD), which catalyzes the dismutation of superoxide radicals into oxygen and hydrogen peroxide, providing systemic antioxidant defense.
A synergistic approach combining these antioxidants has been shown to reduce oxidative biomarkers and improve poultry performance under heat stress conditions.
2.4. Functional Osmolytes and Bioactive Feed Additives for Heat Resilience
Bioactive compounds and osmolytes enhance cellular integrity and physiological performance during episodes of elevated ambient temperature.
- Betaine (Trimethylglycine): Serves dual functions as a methyl donor in metabolic reactions and as an osmolyte that stabilizes cellular hydration by regulating intracellular osmotic pressure. Betaine supplementation improves intestinal morphology, enhances gut barrier function, and reduces energy expenditure associated with osmotic regulation.
- Chromium (Cr): Especially in its organic form (e.g., chromium picolinate or chromium propionate), chromium reduces circulating corticosterone, enhances glucose utilization, and improves growth and feed conversion efficiency under thermal challenge.
- Phytogenic Feed Additives (PFAs): Including essential oils, flavonoids, tannins, and saponins, PFAs exhibit anti-inflammatory, antimicrobial, and antioxidant properties. They also modulate gut microbiota and reinforce intestinal immunity.
- Probiotics and Prebiotics: Probiotics (e.g., Lactobacillus, Bacillus, Bifidobacterium) enhance gut microbial balance and improve mucosal immunity. Prebiotics (e.g., fructooligosaccharides, inulin) serve as substrates for beneficial bacteria and support gut health and systemic immunity, both of which are often compromised during heat stress.
2.5. Fortification of Micronutrients for Thermotolerance and Physiological Support
Micronutrient requirements escalate during heat stress due to both increased metabolic activity and reduced dietary intake. Specific vitamins and minerals support critical biological functions:
- Vitamin A: Maintains epithelial integrity and promotes mucosal immunity, providing a first-line defense against infection.
- B-complex Vitamins (B1, B2, B6, B12, niacin, pantothenic acid, folic acid): These coenzymes are vital for mitochondrial energy metabolism, neurotransmitter synthesis, and stress recovery pathways.
- Magnesium (Mg): Plays an essential role in neuromuscular transmission, enzymatic activation, and regulation of corticosteroid release, offering protective effects against neurogenic stress responses.
Periodic evaluation and reformulation of vitamin-mineral premixes are crucial to adapt to varying environmental challenges and flock performance dynamics.
2.6. Strategic Water Management for Thermoregulation and Hydration
Water is the most critical nutrient during heat stress. Birds increase their water intake to facilitate evaporative cooling, excrete excess body heat, and maintain fluid-electrolyte balance.
- Unrestricted access to clean, cool water (ideally maintained below 25°C) is essential to prevent dehydration and support physiological thermoregulation.
- Drinking water should be supplemented with electrolytes, vitamin C, organic acids, or acidifiers (e.g., citric acid, lactic acid) to promote rehydration, gut health, and nutrient utilization.
- Target a water-to-feed ratio of ≥2.5:1, particularly during heat waves, to meet the elevated water requirements for evaporative cooling and metabolic homeostasis.
The inclusion of water quality management protocols (e.g., monitoring pH, total dissolved solids, microbial load) further ensures effective nutrient delivery and mitigates heat-related health issues.
3. Smart Feed Management for Heat-Stressed Birds
Optimize feeding routines to support intake and efficiency during hot conditions:
- Time it Right: Offer feed during cooler hours (early morning and late evening) to stimulate appetite.
- Go Pellet Smart: Use pelleted feed to boost nutrient density and reduce feed wastage.
- Trim the Fiber: Lower dietary fiber to minimize fermentation-related heat in the gut.
4. Quick-Glance: Nutritional Tools to Combat Heat Stress
| Key Nutrient / Strategy | Purpose & Benefit |
| ???? Lipid-Based Energy | Lowers metabolic heat, maintains energy intake |
| ???? Essential Amino Acids | Supports lean growth with less heat from protein metabolism |
| ???? Electrolyte Balance | Regulates hydration, acid-base balance, and muscle function |
| ???? Vitamins C & E | Fight oxidative stress and strengthen immunity |
| ???? Selenium, Zinc, Chromium | Enhance antioxidant defenses, lower stress hormone levels |
| ???? Betaine | Acts as a cell protector and energy saver under heat stress |
| ???? Probiotics & Prebiotics | Promote gut health and immune resilience |
| ???? Water Intake Management | Vital for cooling, nutrient transport, and digestion |
5. Conclusion: Building Heat Resilience Through Nutrition
Nutrition is a cornerstone of heat stress management in poultry. By incorporating energy-dense ingredients, fine-tuning electrolytes, and adding protective nutrients like antioxidants and osmolytes, producers can greatly reduce the harmful impacts of high temperatures.When combined with sound environmental and management strategies, these targeted nutritional interventions offer a powerful, integrated solution to maintain poultry health, welfare, and productivity even in extreme climates.