Cows & Heat
Evaporation
Off-loading heat by evaporation is the most efficient way for cows to rid themselves of heat load – it is the primary mechanism for heat loss. Anything you can do to assist the cows’ evaporative cooling processes is worthwhile.
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Evaporation - heat loss through sweating and breathing
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70% of total evaporative heat loss is due to sweating.
30% of total evaporative heat loss is from breathing – moisture losses from the respiratory system.
Small evaporative heat losses also occur through loss of water vapour from skin independent of the action of sweat glands, and through salivation.
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Evaporation from the cow’s surface through sweating will increase with air movement. However, evaporation depends on a difference in relative humidity between the cow’s skin and the air. For example, at 30oC you may be able to achieve good evaporative heat loss in low humidity conditions. If the temperature remains at 30oC but the humidity level increases, then the rate of evaporative heat loss will decline - keep this in mind when making cooling choices for your cows.
Once the air temperature exceeds the cows' body temperature, heat loss can only occur by evaporation.
Sprinklers and fans work best to support a cow's evaporative heat loss process but only in low humidity conditions.
