Occurrence: Worldwide, but especially in hot, humid areas of the world.   Species affected: All. Heavier breeds are more susceptible.   Age affected: Older birds (over 5 weeks) and adults.

Causes: High outside temperatures (reaching 100ºF) and high humidity (reaching 90% or more) combined with inadequate ventilation of poultry houses.

Effects: Birds have no sweat glands, so their only method of cooling is by rapid respiration with mouths open, and hanging wings loosely by their sides. Birds become weak and feed consumption decreases. If continued for several days or weeks, birds will die due to respiratory, circulatory or electrolyte imbalance. There is a dramatic drop in egg production and shell quality will deteriorate.

Older birds (over 5 weeks) and adults (especially heavy breeds) in production are more susceptible to high temperatures accompanied by high humidity. Lacking sweat glands, the birds’ only method of cooling is by rapid respiration with mouths open and wings relaxed and hanging loosely at their sides.

When outside temperatures approach 100oF (38oC) and relative humidity reaches 90%, body temperatures rise, the birds become week and feed consumption is decreased. If this continues for several days or weeks, the birds may die due to respiratory, circulatory, or electrolyte imbalances.

Birds in production will show a dramatic decrease in egg production and shell quality will deteriorate.

Clinical signs are diagnostic at high environmental temperatures.

Every attempt should be made to improve air circulation with additional fans. Insulation of the building and use of white or aluminium paint on the outside of the building will reflect heat. Water sprinkers can be installed on the roof or over side curtains to cool the house.

Installation of high pressure foggers in the ceiling or evaporation coolers on the side walls will also significantly reduce inside temperatures when the relative humidity falls below 75%.

A system of tunnel ventilation (exhaust fans at one end of the house and air inlets at the other end will provide significantly more efficient cooling and heating throughout the year). Reducing bird concentration and providing birds cool water with vitamin C, electrolytes and/or aspirin will also reduce heat stress.

Increasing the nutrient density of the feed (increased energy and protein) and feeding early in the morning are also important during hot weather when the birds’ feed intake is less.

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