Heat Stress


6 min read

Why do cows get hot so easily? How to recognise heat stress in cows Minimising heat stress Podcast Additional resources

Heat stress in cows happens when they can't dissipate the heat they generate, leading to discomfort and lower milk yields. Unlike humans, cows can start feeling heat stress at temperatures above 20°C. You might notice that your cows breathe faster, graze less, drink more, and move slower in warm weather. Providing shade and ample drinking water is the first line of defence against heat stress. You can also make strategic changes to their management and feeding routine. The podcast included here provides scientific explanations and in-depth strategies for managing heat stress.

Why do cows get hot so easily?

Heat stress occurs when cows have more heat than they can get rid of and leads to discomfort and lower milk production. All areas of New Zealand get hot enough to cause heat stress during summer.

Which animal monitoring technologies are farmers using in 2023?

We all have an ideal temperature range within which we feel comfortable and our immune system and organs function properly. The comfortable temperature range for a cow is 4-20°C, lower than for a human of 16-24°C.

That’s because cows generate enormous amounts of energy digesting food and producing milk. This is handy during winter but a challenge during summer, when cows absorb more heat from the environment and it’s harder for them to maintain an ideal body temperature.

One way cows get rid of excess heat is by evaporation through their breath and sweat. To increase evaporation, they breathe faster and sweat more, although their ability to sweat is limited. When this isn’t enough, they eat less to reduce the production of heat in their rumen, so their milk yield declines.

High humidity, little cloud cover, and low air movement increase the risk of heat stress as evaporation is less effective, making it hard for the cow to lose heat by sweating and panting.

How to recognise heat stress in cows

Watch for these five signs:

  1. Cows breathing faster – check their breathing rate
  2. Eating less - cows standing more but grazing less
  3. Drinking more and cows hanging around troughs
  4. Cows walking more slowly to and from the shed
  5. Less milk in the vat

Checking breathing rate

The earliest indicator of heat stress is increased breathing rate. Check breathing rate by observing a number of cows on a warm summer afternoon – a high producing black cow will be most at risk. More than 10 breaths in 10 seconds means a cow is not comfortable and is an indication that the herd need cooling.

Minimising heat stress

To minimise impacts on productivity and protect cow comfort, consider the following:

Providing shade

Cows are highly motivated to seek shade during hot weather because shade will keep the cows 2 degrees cooler than direct sunlight.

  • Use paddocks with shade during periods of heat stress –at least 5m2 of shade per cow to minimise competition.
  • Provide shade at the shed and over off-paddock facilities.
  • Use shade cloth with at least 80% shade block.
  • Consider a tree planting program on the northern and western edges of pastures, and deciduous trees along raceways (see Trees for Shade).

Using sprinklers can keep cows cooler for 2-6 hours

Cooling with water

Sprinklers can improve evaporative cooling for 2-6 hours after wetting.

  • Wet the dairy yard before cows arrive to remove heat from the concrete.
  • Ensure all cows are wet in the first 10 minutes of arriving to the dairy shed.
  • If you need to conserve water, run sprinklers on an on/off cycle, for example, around 3 minutes every 15 minutes.
  • The water should be large droplets to reach the skin and pour down the side of the cow.
  • Position sprinklers approximately 2m above cows to reduce risk of wetting udders and of water getting into cows’ ears.
  • Fans and/or extra space on the yard can increase airflow and cool cows faster by moving humid/moist air away.
  • After a warm night, sprinklers can be used in the morning milking to reduce heat load, especially if there is little shade available for cows during the day.

Note: Sprinklers are not effective unless they thoroughly wet the coat, as this only increases humidity, making heat stress conditions worse.

For technical specifications on sprinkler system design, visit the DairyAustralia website.

Check flow rates. Keep your troughs clean. Cows will drink more and feel cooler.

Drinking water

Lactating cows typically require more than 100 litres/cow/day in summer and drink between two to six times per day. A cow can drink 20 litres per minute.

  • Inspect the troughs at peak drinking times (after milking) and ensure flow rates to troughs are high enough.
  • Water pipes should be 75mm in diameter with enough pressure to provide 20 litres per cow per hour. Large volume troughs will also help maintain supply during high demand.
  • Clean troughs regularly. Cows will drink more water if it is clean and palatable.
  • Consider installing extra troughs in raceways and at the dairy yard.

Install an extra trough along the exit race of the cow shed.


Cows walking to milking and standing on unshaded yards during the heat of the day increases risk of heat stress.

  • Reduce the walking distance and speed to the dairy. Plan to use paddocks closer to the shed for afternoon milkings.
  • Allow more yard space per cow at milking times.
  • Reduce the time spent in unshaded yards by milking earlier in the morning and later in the afternoon or consider once-a-day milking.


Peak heat production in the rumen occurs about three hours after cows eat. The impact of modifying diet is small relative to the impact of providing shade and cooling. However, there are some changes that can help keep your cows cooler:

  • Increase metabolisable energy (ME) and nutrient densities of feed, especially during the day to reduce a drop in appetite due to heat stress.
  • Feed more of their daily allowance earlier in the morning or overnight so that heat is produced during cooler parts of the day.
  • Cows lose more salts in sweat and urine when they are hot so offer extra potassium, sodium and magnesium via salt licks or supplement.


How does heat stress affect cows, what are some warning signs, and what can you do on farm to make life more comfortable for your cows? In this episode, Tom Buckley, farm manager for Owl Farm in Cambridge, goes into detail about the strategies they use to combat heat stress. Meanwhile, DairyNZ’s Jac McGowan talks about the science behind heat stress: how it affects cows, the warning signs, and what research is underway.

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Last updated: Jan 2024
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