Heat stress is a worldwide problem in poultry production, especially in broiler and layer farms.
Heat stress begins when the ambient temperature is above 85F0 due to which physiological changes start within the bird’s body to dissipate excess heat. If this condition persists it will affect optimum growth rate, hatchability, egg size, eggshell quality, and egg production.
High ambient temperature can be devastating to commercial broilers; occupied with high humidity they can have even more harmful effect. Heat stress interferes with the broiler comfort and suppresses productive efficiency, growth rate, feed efficiency, carcass quality, increased time to reach market value and high mortality.
In laying hens, Heat stress leads to a decline in egg production and egg quality, as well as, the shelf life of an egg is also decreased. In breeder high ambient temperature coupled with high humidity decreases fertility leading to low hatchability.
During this period the increase in body temperature has a negative effect on gamete formation and fertilization process. Hens must make major thermo-regulatory adaptations to prevent death from heat exhaustion due to which full genetic potential of the layer is often not achieved.
Clinical Signs and Symptoms of heat stress: Poultry subject to high environmental temperatures exhibit many behavioral and physiological changes which allow them to re-establish heat balance with their surroundings.
As ambient temperature increases above the comfort zone, the bird spends less time in feeding while more time in drinking, panting with their wings elevated and more time resting.
Usually, their wings are spread away from the body to promote cooling by reducing body insulation and they splash water on combs and wattles in order to increase evaporative cooling from these surfaces. Heat-stressed birds also spend relatively less time engaging in social behavior and in changing posture.
In open houses, birds will look for a shady and cool area. Within the bird, blood flow is diverted from certain internal organs such as liver, kidneys, and intestine to dilated blood vessels of peripheral tissues(skin) in order to facilitate heat loss.
Measures to alleviate heat stress in poultry
Housing Design: The design of the building and its ventilating system, the sitting of new buildings and construction materials, will have an effect. Roof color, reflectivity, pitch and orientation,
And whether the building is in shade or not, are the factors which will have a small bearing on solar heat gain. Expert advice should be sought at the design stage. The house and ventilation system must complement each other to achieve maximum benefit.
All naturally ventilated houses must be equipped with some type of adjustable side wall curtains to control the flow of air into the house. To minimize heat stress-related problems during hot weather, it is always beneficial to insulate poultry house roof/ceilings.
The methods used for insulation are; dropped ceiling, rigid board insulation, spray polyurethane insulation, reflective insulation, etc. Similarly, reflective roof paints have been shown to reduce roof temperature thus reducing heat gain.
Air Movement: Increasing the amount of air over a bird is one of the most effective methods that producers can use to increase heat removal from birds. High airspeed is essential in heat stress relief especially in systems with lower stocking rates.
Ventilation: During the summer when the temperature and humidity are high, proper poultry house ventilation is vital to ensure the necessary removal of heat and continued productivity of the flock.
The ventilation system has several components including curtains, fans, fogging nozzles, evaporative cooling pad, timers, static pressure controller, thermostats, etc. Most ventilation systems can provide an adequate indoor environment when properly managed.
In control houses, a new arrangement for ventilating poultry houses in the summer is Tunnel ventilation. It involves moving air along the building axis from inlets to exhaust fans, providing high airflow velocities. This system works best when there is no pressure difference between inlet and fans.
Evaporative cooling: It is an essential component of a hot weather ventilation system. There are two cooling systems used in poultry houses: fogging system and pad system.
While the pad system can only be installed in a power-ventilated house, fogger system can be installed in power or naturally ventilated housing to lower the temperature of the house. A third system, sprinkling, has limited usage except in very dry climates.
Stocking Density: Heat loss often depends upon the difference of temperature in house and bird’s body. If stocking density is high, the radiant heat between birds increases thus increasing house temperature.
Birds tend to absorb each other radiant heat load which makes heat management more difficult. That’s why it is sound practice to reduce bird density in summer so that birds can move freely to nearby waterlines.
Drinking water and feeding time: During heat stress, the bird tries to maintain its body temperature by increased respiration (evaporation of metabolic water) which may considerably increase water requirement.
Feeding at the right time of day is very important to help birds cope with heat stress. A good strategy to take an unnecessary heat loss off the birds is to withdraw feed 8 hours prior to the anticipated time of peak temperature.
One-third of the daily feed ration should be given in the morning and two third in the late afternoon. So, called “midnight snack” are a good tool to give hens extra feeding time in cooler parts of the night.
Nutrient Requirement: In summer, a very direct way to ensure optimum nutrient intake despite decreases in feed consumption is to increase the nutrient density of the ration.
The feed should be made denser with nutrients, vitamins, and minerals to compensate for low feed intake. Thus, as the hot season progresses it may be necessary to fine-tune feed formula again in mid-summer.
Conclusion: Both climate change and poultry productions have always negative impacts one over the other. Climate change is one of the most important environmental stressors challenging poultry production worldwide. The negative effects range from reduced growth rate and egg production to decreased poultry egg quality and safety.
Recently, two innovative approaches have been explored, including early life conditioning (i.e. perinatal heat acclimation) and genetic selection of breeds with increased capacity of coping with heat stress conditions (increased heat tolerance). However, these potential opportunities, although promising still to require further research and development.
Authors: Muhammad Rumman Aslam, Haseeb Ajaz, Mujeeb abid