Ventilation: air flow
Ventilation is an important factor in housing. A building with open sides is ideal, otherwise
cross-ventilation at bird-level should be allowed for in the form of floor level inlets, open in a
direction to allow the prevailing wind to blow across the width of the building. An air mass
between the side walls of a poultry house resists being moved, even across an open-sided
building. The wider the building, the more the resistant it is to air movement. Buildings over 8
m (26 ft) wide have a significantly greater problem because of this inherent property of air to
resist movement. It is recommended that buildings relying on natural airflow for ventilation
should not exceed 8 m in width.
Heat stress is a significant constraint to successful production and can lead to death.
Although birds can withstand several degrees below freezing, they do not tolerate temperatures
over 40 qC. This depends on the relative humidity prevailing at the time. Poultry do not possess
sweat glands and must cool themselves by panting out water in their breath, which is
evaporative cooling. When the humidity is too high, this cooling mechanism does not work very
well. Lethal temperatures for most chickens are 46 qC upwards, and severe stress sets in above
40 qC. In temperate regions, the chicken house may be constructed to face the rising morning
sun to gain heat. In the tropics however, an east-west orientation of the length of the building
helps to minimize exposure to direct sunlight. Building materials such as tin or other metal
should be avoided for this reason, although white paint will reflect up to 70 percent of incident
solar heat radiation. Ventilation concerns in building alignment may prevail over solar heat
control in this aspect, as cross-flow ventilation requires the side of the building to face the
Ground cover can also reduce reflected heat. Shade should be provided, especially if there is little air movement or if humidity is high. With no shade, or when confined in higher
temperatures, poultry become heat stressed and irritable, and may begin to peck at one another.
When new pinfeathers are growing (especially on young stock), blood is easily drawn, which
can lead to cannibalism. The effects of heat stress are:
x a progressive reduction in feed intake as ambient temperature rises;
x an increase in water consumption in an attempt to lower temperature;
x a progressive reduction in growth rate; and
x disturbances in reproduction (lower egg weight, smaller chicks, reduced sperm
concentration and an increased level of abnormal sperm in cocks).
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Ventilation: air flow