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By K.V. Chandrasekar, Kemin AgriFoods, Singapore
Chickens, unlike most other animals, do not possess sweat glands to aid in heat loss in order to maintain a constant body temperature. The chicken removes excess body heat in four ways. Body heat can be lost by radiation from the skin surface through the air to another object (i.e., another bird). Heat can be directly transferred by conduction to cooler objects with which the bird is in contact, such as the cage, litter or slats. Body heat is also lost to the surrounding air by convection.When the environmental temperatures are between 28°C and 35°C (82°F and 95°F), radiation, conduction, and convection heat losses are usually adequate to maintain the bird’s body temperature. The bird dilates the blood vessels in its skin, wattles and comb to bring the internal body heat to the skin surface to facilitate conductive, convective and radiation heat loss. Floor birds will search for cool places in the house and dig into the litter to increase the conductive and convective heat loss. Drooping of the wings promotes convective heat loss by increasing the surface area of the body.
Caged birds are more susceptible to heat stress because they are unable to seek a cooler place and there is less conductive heat loss in cages. As the environmental temperature approaches the body temperature of the bird, 41°C (106°F), the efficiency of these heat loss mechanisms diminishes.
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Source: Source: World Poultry, Vol. 27, No. 5, 2011
