Heat stress is caused by various environmental factors such as air temperature, air humidity, air velocity and exposure to direct sunlight.

Heat stress affects the activity, production and health of your livestock. Research has shown that at temperatures of 22°C and above, livestock show a reduced feed intake and consequently lose body weight. Production is reduced and can remain below standard for an extended period.

The optimum ambient temperature for livestock is between -5°C and 18°C. At least two months per year, the temperature in the Netherlands exceeds the critical value of 20°C. Under normal circumstances, livestock keep their body temperature within the limits of 38 to 39°C by sweating and panting. Heat is removed by increasing the rate of respiration and evaporation through the skin.

For example, above a temperature of 18°C, it takes extra energy for a cow to remove heat. At these high temperatures, livestock are barely able to regulate their own body temperature.

A cow, for example, can produce 20 to 25 litres of water vapour per day in extreme conditions. Because a cow has to limit its own heat production, it will move less during heat stress (less muscle work) and eat less feed (less digestive work). Feed intake can decrease by up to 25%, which is one of the causes of reduced milk production. Panting and sweating also costs energy.