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Heat waves, according to the World Meteorological Organization (WMO), “occurs when, over an interval of at least 6 consecutive days, the daily maximum temperature is 5°C higher than the daily average value of the reference period”.
As direct negative effects on the performance of commercial laying hens caused by high temperatures and relative humidity are:
Reduction in feed consumption.
Drop in production.
Reduction in egg quality and, mainly,
Increased mortality rate.
If we evaluate what is happening lately, we perceive that the occurrences of heat waves are more and more present in our reality.
In this context, it can be said that heat stress is related to the result of the negative balance between:
The amount of heat dissipated from the animal to the surrounding environment and,
The amount of heat produced by the animal itself.
If we consider that the best condition would be the maintenance of thermal equilibrium, stress is precisely the imbalance that leads the animal organism to use different ways to maintain itself.
Birds are homeothermic animals, that is, they keep their body temperature relatively constant (approximately 41°C), but their characteristic is the absence of sweat glands, which makes heat exchange with the environment difficult.
Because of this, birds can exchange heat with the environment by four means in order to keep their body temperature in equilibrium:
Convection.
Conduction.
Radiation.
Respiration.
Respecting the limits of the thermoneutrality zone for laying hens under “normal conditions” is no longer an easy task and it is not adopted by everyone. Under heat wave conditions, the losses incurred are very significant from an economic point of view due to high mortality rates, as has occurred in Brazil in the spring and summer period.
Considering the ideal temperature ranges for a rearing system, the following figure shows the recommended limits for the different phases during rearing and production.
Figure 1. Recommended ideal temperature ranges for laying hens in the rearing, rerearing and production phases (Silva et al., 2020).
In a simple direct analysis it is possible to conclude that in case of heat waves the production conditions will be well above the recommended ideal temperatures.
In addition to the conditions related to temperature, the relative humidity values of the air must be associated in ...
