Introduction

Poultry are homeothermic animals with a normal body temperature range of 41–42°C. Under optimal thermal conditions, typically defined as the thermal neutral zone (18–22°C), birds can maintain their core temperature without expending additional energy. However, deviations from this range, particularly during brooding when higher ambient temperatures are necessary, impose significant physiological and behavioural adjustments. Environmental temperatures exceeding 25°C are sufficient to induce heat stress in poultry, which has profound effects on health, performance, and welfare.

Indicators of Heat Stress in Poultry

Behavioural Adaptations:
Poultry exposed to elevated temperatures exhibit distinct behavioural changes, including:

• Reduced feed intake
• Increased water consumption
• Panting
• Decreased mobility
• Elevation of wings to expose less-feathered areas for heat dissipation

Physiological Responses:
Heat stress triggers several physiological disruptions, including:

• Oxidative Stress: Resulting in impaired gut funtion, increased susceptibility to disease, and reduced growth rates.
• Disturbance of Acid-Base Balance: Characterized by respiratory alkalosis and metabolic acidosis, negatively impacting production performance.
• Immunosuppression: Evidenced by reduced antibody production and lowered white blood cell counts.

These alterations collectively compromise gastrointestinal functionality, reduce nutrient absorption, and increase intestinal permeability. Dysbiosis, characterized by a decline in beneficial microbiota and a concurrent rise in pathogenic populations, can lead to necrotic enteritis.

Neuroendocrine Changes:
Heat stress activates neuroendocrine pathways that elevate blood glucose levels and respiratory rates. These adaptations, while aimed at coping with hyperthermia, reduce growth efficiency and reproductive performance.

Nutritional Strategies for Mitigating Heat Stress

To counteract the adverse effects of heat stress, several dietary modifications can be employed:

1. High-Energy Diets:
   Incorporating fats, which generate less metabolic heat compared to proteins and carbohydrates, enhances energy availability without exacerbating heat production.
2. Pelletized Feed:
   Feeding pelletized diets can improve feed intake and nutrient utilization under heat stress conditions.
3. Gut Health Enhancement:
   Indirect nutritional strategies, such as the inclusion of prebiotics, probiotics, organic acids, exogenous enzymes, and essential oils (e.g., oregano and thyme), can bolster gut integrity and mitigate the deleterious effects of heat stress.
4. Supplementation of Vitamins, Minerals, and Phytochemicals:
   Specific nutrients with antioxidant and immune-supportive properties have proven effective:

Supplement	Beneficial effect of heat stressed birds:	Recommended dosage
Vitamin E	Antioxidant; enhances lymphocyte proliferation	100-250mg/kg
Vitamin A	Antioxidant and improves immunity
Vitamin C	Reduces oxidative damage and boosts immunity	200-250mg/kg
Zinc	Is associated with the antioxidant defense system, immune function, and skeletal development	40-60mg/kg organic Zn
Selenium	Vital component of proteins which are different parts of enzymes in physiological processes.	0.15 – 0.3mg/kg
Electrolytes	Higher range of dietary electrolyte balance (DEB): 200-300mEq/kg (use of Sodium Bicarbonate and Potassium Chloride)
Phytochemicals	· Lycopene (found in tomatoes) · Resveratrol (found in grapes, berries) · EGCG (green tea extract) · Curcumin (extracted from turmeric) · Other with antioxidant properties:  Thymol, Carvacrol, Cinnamaldehyde, Silybinin and Quercetin.	·      Lycopene 200-400mg/kg ·      Resveratrol (300-500mg/kg) ·      EGCG 300-600mg/kg) ·      Curcumin 100-150mg/kg
Osmolytes	· Betaine (increase water-holding capacity of the cells, thus preventing dehydration) · Taurine (antioxidant action)	Betaine: 0.05-0.2%   Taurine: 5g/kg feed

 

Conclusion

Through targeted dietary interventions, poultry producers can alleviate the detrimental effects of heat stress, safeguarding poultry health, welfare, and productivity. The adoption of these strategies provides a holistic approach to enhancing thermotolerance and maintaining performance under challenging environmental conditions.

Reference

Wasti, S., Sah, N., & Misha, B. (2020). Impact of Heat Stress on Poultry Health and Performances, and Potential Mitigation Strategies. Animals, 10(1266).