Heat stress: causes, facts and prevention

The optimal outside temperature for dairy cattle lies between 23°F and 64°F. Heat stress is caused by a combination of high temperature and high humidity. At a temperature of 68°F and a humidity of 80%, a cow is already suffering from heat stress. Literature and practice have indicated that heat stress impacts the activity, milk yield and health of cows. As a result of this, the number of voluntary visits of cows to the robot will decrease, which means a negative impact on farm performance. Using the Lely Benchmark tool, we have analyzed this.

Management, Cow health, Milking

Benchmark facts

Based on the ‘Royal Dutch KNMI’ weather institute we used the Lely Benchmark environment to analyze a normal week and a warm week in the Netherlands in 2013. Average day temperature during the normal week was 62°F (including the nights); in the warm week this average temperature was 70°F (including the nights). First of all, milk production per cow per day and milkings per cow per day were analyzed. In figure 1 we see a significant difference for both parameters; both milk production and number of milkings were at a lower level during the warm week.

Figure 1

In terms of refusals (figure 2) we also see a significant difference; the number of refusals dropped during the warm week. This could be explained by the fact that the cows were less active and tried to avoid physical efforts. A decrease of the number of milkings and refusals leads to an increase of free time; the percentage of free time rose significantly during the warm week. The number of failures shows no significant difference.

Figure 2


This Benchmark analysis proves that heat stress has a negative influence on the cows’ performance. Several measures are possible to ensure that cows — dry cows and heifers included — do not suffer from heat stress. First and foremost, such measures are related to water supply, housing and feed management. These aspects have a direct impact and preventive measures can be taken with little effort.

• Check ventilation capacity and increase ventilation rate if necessary (mechanical ventilation, doors open, curtains open) to ensure a maximum air flow.
• Control water management; make sure that at least 10% of all cows can drink simultaneously from large open troughs.
• Check the capacity of your overall water supply system.
• Check cleanliness of water troughs every day.
• Fermentation of roughages produces a lot of warmth. Consider a temporary increase of the amount of concentrates in the ration.
• Add some salt to the ration. 
• Feed multiple times a day.

Push up the feed multiple times a day to prevent the feed from heating up and therefore becoming less palatable. During hot periods, it is advisable to put the cows out to pasture only during the night or during the cooler moments (evening, early morning) of the day. When in pasture, cows should always be ensured of sufficient shade and fresh water.

Lely Farm Management Support