What is Heat Stress ?

• A situation when chicken faces difficulty in achieving balance between body heat production & body heat loss
• Genetics, Feather cover, Age, Body Weight, Egg Production stage & flock maintenance all affect a chicken’s heat tolerance
• Chickens are homeotherms & regulate their body temperature across a wide range of external Temperature.
• But continuous high climate Temp overwhelm the thermoregulatory mechanisms, resulting imbalance between the amount of metabolic heat produced & their capacity to dissipate body heat in the environment

Key environmental factors contributing to Heat stress in poultry

• Consistent Global warming induced Temperature elevation
• Uprooting Trees & Deforestation in the name of urbanization
• Filling of waterbodies
• Indiscriminate Mining & Urbanization in Hills

Physiological Changes and Production Impact of Heat Stress

• Chickens lack sweat glands to facilitate latent heat loss by evaporation (perspiration), and have limited un-feathered body surface areas for loss of sensible heat through conduction, radiation, & convection
• With Increase in Climate Temp, the Thermal gradient between the Body surface & the surrounding environment lessens with dissipation of Heat decreasing, resulting chicken suffering from environment-induced Hyperthermia.
• This increases Respiratory rate (Thermal Polypnea or Panting) to increase Latent Heat Loss via Evaporation of water from the Respiratory tract
• Dehydration is the most harmful effect of panting, which causes Respiratory Alkalosis, acid base imbalance leading to permanent physiological damage
• Alkalosis reduces blood ionized Calcium and ultimately Eggshell mineralization resulting Reduced Egg production, Pale Egg, Soft Shell Eggs, Thin Shell Egg, Increased Broken egg % in Layer & Breeder
• Panting causes Oxidative Stress leading to Immunosuppression, ultimately inviting diseases
• Panting causes loss of energy leading to poor productivity in chicken
• Heat Stress impact the Expression of Gene related to Growth, Production Performance & Resistance to disease

Key signs of heat stress in poultry

• Panting
• Sitting with Wings spread to dissipate body heat by Convection
• Poor Feed Intake
• Increased water intake
• Enteritis
• Poor Body Wt gain, reduced Egg Production & Poor Egg shell quality
• Heat Stroke Mortality

Economic impact and productivity losses associated with heat stress

• Reduced Feed Intake
• Reduced Egg Production
• Reduced Egg Weight
• Poor Shell Quality
• Reduced Albumin Height in Egg
• Reduced Male Fertility
• Reduced Hatchability
• Poor Growth
• Cannibalism
• Respiratory Distress leading to Respiratory Infections like Colibacillosis, CRD, Coryza, ND, IB & Avian Influenza
• Immunosuppression resulting increased disease incident from existing microbes, especially the respiratory diseases like ND, Avian Influenza, IB, CRD, E coli, etc
• Heat Stress has Permanent damaging effect; damages the muscles affecting Meat Quality and Lowering Breast Muscle Yield
• Reduces Protein content of the muscles, reduction of muscle pH & Water Holding Capacity and ultimately affecting Juiciness of Chicken Meat
• Disturbs Lipid metabolism by affecting enzyme function in lipid breakdown causing Excess Fat deposition instead of converting to meat

Major Health risks of chicken during summer

• Immunosuppression and increased incidence of diseases from existing microbes, especially the respiratory diseases like ND, AI, IB, CRD, E coli, etc.
• Oxidative Stress causes Gut Health Problem, reduced Digestion with Reduced Productivity
• Under Heat Stress, water intake increases leading to dilution of Nutrients inside intestinal lumen resulting mal-absorption and passage of nutrients into the hind gut
• This favours growth of undesirable microorganism, loss of microbial equilibrium in the gut, Dysbacteriosis, Enteritis, Watery dropping, Wet Litter condition, Ammonia accumulation resulting further increase in Humidity at the bird’s level leading to increase discomfort level & dehydration. The chicken will consume more water and the condition aggravates in a cyclic manner (Vicious cycle)
• In closed EC house, with Increase in climate Temperature, control system is failing, especially with high Humidity outside. Evaporative Cooling & Tunnel Ventilation failed to maintain Comfort environment inside with rising Climate Temperature outside creating many Blank spot in the middle of EC house causing Breathing problem leading to Panting

Impacts on immunity, post vaccination response & disease susceptibility

• Heat stress impairs a chicken’s immune system, leading to a reduced response to vaccines, suppressing the production of antibodies and affecting the function of immune cells, particularly lymphocytes, due to the atrophy of immune organs like thymus under high temperatures. Heat stress makes it harder for chickens to fight off infections after vaccination and increases their vulnerability to disease
• Heat stress can significantly lower the levels of circulating antibodies (like IgM and IgG) produced after vaccination, resulting in a weaker immune response against pathogens
• High Temp cause atrophy of thymus, leading to decreased T-cell production and impaired cell-mediated immunity
• Heat stress increases corticosteroid levels and thus the immune system.
• Heat stress disrupt the function of immune cells, macrophages & lymphocytes, affecting their ability to recognize and fight pathogens.
• Heat stress damage the intestinal lining, allowing harmful bacteria to enter the bloodstream, further compromising immune function

Monitoring Heat stress in poultry

• Difference in activity during Cool hours & Hot hours
• Posture of the birds
• Feed Intake with increasing Temperature
• Health status after Temperature increase
• Degree of Panting or Respiratory distress
• Egg Production & Egg Shell quality status with Increasing Temp

Poultry House Environmental modifications to combat Heat Stress

Poultry House Environment need to made near comfort zone in terms of Temperature Humidity & Ventilation. Closed EC house is the perfect answer for chicken. Alternative actions are:

• Plantation of Tress on both side
• Farm construction near forest or under Coconut farming or any big trees
• Reduce Stocking Density
• In open house system action must be taken to REDUCE TEMPERATURE at Birds level through
  1. Elevated Roof, increased centre height than standard practice
  2. Coated Roofing materials (Tin or Asbestos) or thatched roof
  3. Extended both side roof overhang to prevent entry of direct Sunlight
  4. Thatching of Roof by Agricultural waste
  5. False Ceiling by Thermostat Aluminium foil or agricultural waste
  6. Constructing Side Pandals (Leaned Roof Over-hang 1 meter)
  7. Hanging of Gunny with Dipper on both side during hot hours keeping ventilation on top
  8. Ceiling fans in case of Broiler and Circulatory fans in Layer or breeder
  9. Springler on Rooftop
  10. Fogger inside the shed

Nutritional Modification to combat Heat Stress in Summer

1. Sodium bicarbonate

• • pH regulation: When birds pant heavily in hot environments, birds lose carbon dioxide due to excessive Panting, leading to a rise in blood pH (alkalosis). Sodium bicarbonate acts as a buffering agent, providing bicarbonate ions that help maintain a balanced blood pH.
  • Improved feed and water intake: Adding sodium bicarbonate to drinking water helps increase water consumption, which is vital for heat regulation.
  • Enhanced growth performance: Studies shown that supplementing sodium bicarbonate in the diet of heat-stressed poultry can improve body weight gain and FCR.
  • Eggshell quality: For laying hens, sodium bicarbonate helps maintaining good eggshell quality as the bicarbonate ion is involved in shell formation.

2. Electrolytes

• • Electrolytes help maintaining proper fluid balance and blood pH levels, which are significantly disrupted when chickens panting heavily in hot environments, leading to the loss of essential minerals like Na & K through their respiratory system
  • Supplementing electrolytes in the drinking water can help replenish these lost minerals and alleviate the negative effects of heat stress

3. Vitamin C

• • Antioxidant activity: Vitamin C scavenges free radicals generated during heat stress, protecting cells & tissues from Oxidative stress induced damage
  • Immune system support: Vitamin C is vital for proper immune function, which can be compromised under heat stress.
  • Hormone regulation: Vitamin C is involved in the synthesis of stress hormones, helping to manage their levels during heat stress.
  • Improved performance: Supplementation with Vitamin C can lead to better growth rates, feed efficiency, and egg production & egg shell quality in heat-stressed chickens. Vit C helps maintaining sperm production in breeder male during summer stress
  • Reduced oxidative damage: Heat stress can cause oxidative damage to the liver and other organs, which Vitamin C helps to mitigate.
  • Blood pH regulation: Studies suggest that Vitamin C can help maintain proper blood pH levels, which can be disrupted under heat stress

4. Ginger, Turmeric few other herbs can help by reducing mortality, improving nutrient digestion, and stimulating the immune system

5. Vit A, D, E & Vit B Complex help reduces heat stress mortality

6. Vitamin E, Zn & Se can help mitigating heat stress with antioxidant parameter

7. Betaine help with reducing metabolic heat production thus helps reducing heat stress

8. Chromium

• Chromium enhances insulin sensitivity, allowing better utilization of glucose, crucial for energy production during heat stress when energy demands are high
• Chromium addition can lead to decreased levels of corticosterone, a stress hormone released in response to heat stress, thereby promoting a calmer physiological state
• Chromium as antioxidant, helps to combat oxidative stress caused by heat stress damaging cells and tissues
• Performance Improvement: by mitigating the negative impacts of heat stress on metabolism & stress response, supplementing chromium can positively influence growth rate, feed efficiency, and egg production in chicken

Drinking Water Management

Cold drinking water supply 24 hours; the key of combating heat stress, can be ensured by:

• Frequent filling of water tank, and not to allow water to become hot in tank
• Keeping water Tank under shed, even inside farm shed.
• Open Tank may be made white painted to reduce heating of water inside.
• Underground water pipeline from tank to farm shed
• Covering of external water pipeline by wet gunny during summer days
• For manual chick drinker, change water frequently

Heat Stress Mitigation Keys

• Reduce Temperature of Poultry house with available Infrastructure & inputs applying common sense
• Reduce Stocking density or allow more space to each birds
• Improve air movement at birds’ level
• Increase nutrient density in feed, especially the micronutrients.
• Modify feeding practice towards cool hour feeding
• Supply cold drinking water 24 hours

For more articles by Dr. B.C, Dutta,  click here