Heat Transfer & Cow Behaviour

Off-loading heat

Understanding the heat exchange process can support your decision making around providing shade, water and cooling systems
to keep cows cool. 

Heat Transfer Process  Behaviours

Conduction - the transfer of heat through physical contact 

Stand up to increase air flow around its body.

Standing in cool drinking water to lose heat through the hooves.

Convection - produces cooling if there's high temperature difference

Stand where there is a breeze or under fans. 

Cooling is more effective with higher air speed

Radiationemission of heat to and from the cow and surroundings, directly from the sun or from re-radiation  from hot ground, fences, buildings etc.

Cows position themselves away from the sun if there is no shade.

Shading from direct sunlight reduces the solar radiation it receives by 50%

Black coated cows absorb more solar radiation.

However, black coated cows will re-radiate heat more effectively at night.

evaporation 

Heat loss by conduction, convection and radiation all depend on a temperature difference between the cow and the surrounding environment. The greater the temperature difference, the faster the flow of heat. As the air temperature rises this form of heat loss declines.

 

Evaporation

This is the most efficient and primary mechanism cows will use to rid themselves of heat loads. Anything you can do to assist the cows evaporative cooling processes is worthwhile.

Heat Transfer Process Cooling benefits
Evaporation - heat loss through sweating and breathing

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.

Evaporation from the cow surface through sweating will increase with air movement. However, evaporation depends on a difference in relative humidity between the cow 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.

evaporation 

Sprinklers and fans work best but only in low humidity.