Why we need a comprehensive strategy for heat stress management?

Temperature and humidity play a critical role in poultry production. Often, in tropical countries like India and Bangladesh, the temperature regularly reaches upwards of 40⁰C which is unfavorable for profitable poultry production. Heat stress is a negative balance between the net energy flowing from animal’s body to surroundings and net energy (heat) produced by the bird (Lucas J. Lara, animals, 2013). Heat stress is one of the most important stressors challenging poultry industry. The negative effects of heat stress lead to reduced growth, reduced egg production and makes birds prone to viral challenges. It is manifested in birds’ behavioral changes, hormonal changes, and immunological changes. Understanding the complex heat stress problem is crucial to control and manage profitable poultry production.
Heat stress is a complex problem
Modern poultry seems to be more prone to negative impacts of heat stress as there’s a higher amount of metabolic activity. There are many changes that may occur when bird is constantly exposed to temperatures above 27⁰C i.e. above the comfort zone

  • Behavioral changes in birds
    To maintain homeostasis, birds tend to reduce body temperature by manifesting peculiar behavioral signs like reduced feed intake, drinking more water, increased panting, wings raised up and minimum movement with more time spent on resting. While panting is an efficient way for thermoregulation but increased panting leads to respiratory alkalosis which lead to increased CO2 levels and high blood pH which subsequently hinders bicarbonate availability and reduced calcium in blood for eggshell mineralization in layer and breeder birds.
  • Physiological changes
    Increased plasma corticosterone due to neuroendocrinal changes may lead to multiple effects like hyperglycemia and immunosuppression which ultimately lead to lower feed intake and increasedvulnerability to viral challenges. Multiple studies have shown immunosuppressing effect of heat stress on broiler, laying hens and breeder birds. Lower weight of thymus and spleen, lower levels of antibodies IgG and IgM are common findings in heat stressed birds (Aengwanich, J. Vet. Sci. 2008). Under chronic heat stress, bird’s body tend to show increase in levels of reactive oxygen species (ROS) which leads to oxidative stress and further damage the production possibilities. (Droge, W, Physiol., 2002) Dehydration and electrolyte imbalance: There’s a high amount of water and electrolyte (Na+ , K+ , Cl- ) loss in heat stressed birds. Decreased cell permeability and reduced ATP synthesis leads to cellular apoptosis.

  • Impact of heat stress on profitability
    Multiple studies have shown the negative impact of heat stress on birds like reduced feed intake, reduced average daily gain, decrease in egg production, and increase in egg abnormalities. In one of the studies by Farnell, M.B.et al, 2001 showed that chronic heat stress may bring egg production down by 50%. In another study, Warriss et al demonstrated an increase in mortality rate by 3 times while N. R. St-Pierre et al, 1999 showed a drop of >50% in average daily gain and concluded that heat stress can cause up to 15% of total economic loss in poultry annually. A loss of 11 lakh is incurred if there is a drop in production of 5% for a 1 lakh bird layer farm (assuming age between 20 weeks to 32 weeks).

Comprehensive strategy to minimize losses in summer
Drop in feed intake, dehydration, and immunosuppression due to summer stress hits directly to the bottom line of farmer. To minimize these losses, a comprehensive strategy is required.

  • Farm management: general summer management practices to reduce average temperature inside shed like using foggers, white lime paint, curtains, insulating the shed roof and water tank will provide cooling effect. Providing proper ventilation is crucial.
  • Water management: water is the most important nutrient. Birds consume 4 times more water at temperatures above 37⁰C. Maintain regular supply of cool and fresh water with additional water acidifiers and sanitizers.
  • Nutrition Management: right nutritional changes for summer is paramount to tackle heat stress problem. Based on the geographical location and intensity of heat, common practices like
    • Optimizing energy levels through inclusion of fats. The feed passage time decreases with additional fat diet, this will help in improving availability of nutrients for absorption.
      There are many advantages of additional fats in summer like increased palatability to improve feed intake, provides a cooling effect to bird, improves egg weight and shell strength.
    • High protein content during heat stress will increase heat load. Supplementing optimal protein quantity and improved amino acid balance is critical. This will help to reduce wastage and heat load due to nitrogen excretion and improved digestibility
  • Vitamins: Vitamin C plays a critical role in reducing body temperature, reduce corticosterone levels and works as an excellent antioxidant to reduce oxidative stress. Vitamin C also improves immunity and reduces mortality in growing birds infected with IBD (G D Butcher and R D miles, 2011). Vitamin E is also used as an antioxidant and booster for immunity, Vitamin A and Vitamin D3 are also required in additional quantity for eggshell quality and immunity respectively.
  • Trace mineral requirement is increased by 15-20% as there’s an increase in excretion of minerals. Specific trace minerals like organic Chromium supplementation play a critical role in improving both cell mediated and humoral immunity while also reducing glucose concentration in blood and better uptake of glucose by cells. (Ghazi et al, Biol. Trace Elem. Res. 2012)
  • To prevent problems due to respiratory alkalosis due to excess panting, electrolyte and sodium bicarbonate addition is crucial to replace lost ions which improves feed intake and eggshell quality.
    Betaine HCl is an important inclusion for broilers and layers as it regulates the water balance inside cells and prevents dehydration related losses. Also, Betaine is studied to improve immunity in birds.

Maintaining profitability during heat stress is a challenging task. This is because there are multiple physiological and behavioral changes that occur during high ambient temperature which ultimately lead to production losses. A comprehensive strategy which includes efficient nutrition, water and farm management will help in reducing signs of heat stress and bring down overall losses in the farm.
For any further information, you may contact the author at rahul.mittal@kemin.com

by Dr. Rahul Mittal and Dr. Chandrasekar S, Kemin Industries