The temperatures across the country are starting to rise and farmers need to start looking at heat stress within their herds.

As temperatures have remained high for an extended period of time, it is important to ensure that you take measures to prevent heat stress from occurring within your herd.

Heat stress

Cows generally start to suffer heat stress once temperatures pass 20°C; heat stress occurs when an animal’s heat load is greater than its capacity to lose heat.

The most visible symptoms tend to be elevated breathing rates, however, increased water intake and sweating, along with decreased feed intake, are other symptoms.

Key symptoms:

  • Increased breathing rate;
  • Increased water intake;
  • Increased sweating;
  • Decreased milk production;
  • Change in milk composition – milk fat and protein percentages drop (seen in dairy cows);
  • Change in blood hormone concentration (increased prolactin);
  • Changed behaviour – crowding, heavy breathing and standing next to a water trough.


To help mitigate heat stress, farmers should provide cows with as much access to shade as possible and ample cool water, as water intakes rise markedly during heat stress.

On a really hot day, cows can drink anywhere up to 110L/day and they can typically drink at a rate of 14L/min from a trough.

Ensure that all water troughs are checked before cows enter paddocks; cows going without water for any period of time should be avoided.

If the water troughs are empty, the water system on your farm may need to be updated.

water on dairy farms

The warm, dry weather is also impacting on grass quality on farms – with many swards containing a large amount of fibre or low quality grass.

High fibre feed can increase the heat of fermentation in the rumen, thus increasing the heat load of livestock.

Where possible cows should be grazing paddocks with shade from trees and tall hedges during periods of hot weather.

This may mean having to graze more shaded parts of the farm during the day and more open areas during the evening/night.

If moving or handling cattle, farmers should minimise the time cattle are in collecting yards and to reduce handling stress.

Where cattle do become affected by heat stress, it is advisable to isolate the most severely affected animals and provide shade and cooling.

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