Cows generate heat internally (metabolic heat) as a result of eating and digesting feed. Like most mammals, the dairy cow needs to maintain its core body temperature within a narrow range around 39oC – between 38.6oC and 39.3oC to be precise! The core temperature fluctuate slightly throughout the day, reaching a peak in the early evening and a low early morning.


How are my cows coping?

The most useful and practical way to determine how your cows are actually coping with the conditions is to check their breathing rate.

An increased breathing rate is the first defence the cow employs to dissipate heat.

  • On hot days or after an extended period of hot weather, check cows twice daily.
  • Check using a watch and count the number of breaths in at least 20 cows by observing flank movements over a 20-second interval and then multiply by 3.
  • Check your best producing cows first – they will be the first to feel the effects because of the extra heat developed in their gut and the higher tissue metabolic rate from the demands of higher production.


Evaporative loss is the fastest way to cool cows down (i.e sprinkling with water followed by airflow such as fans). If cows are severely affected, hosing thoroughly – so they are wet to the skin is most effective IF there is good air flow and humidity is low. Severely affected cows will likely need a vet visit ASAP as dehydration and kidney damage can be a complication of heat stress

If cows are at more than 60 breaths a minute – take action      


Access to cool drinking water

  • Allow for 200-250 litres per cow per day of drinking water in hot weather – double what cows usually need each day.
  • Ensure cows have access to plenty of cool drinking water wherever they are during the day.
  • A large water trough on the exit side of the dairy is a must.
  • Water troughs in every paddock will keep cows grazing longer in hot weather. If they have to leave the paddock to get a drink they may not bother going back!
  • Large volume concrete troughs help keep drinking water cool.
  • Provide a minimum of 0.75m water trough space per cow at your feed-out facility.
  • Water pipes should be 75mm in diameter, with sufficient pressure to provide 20 litres per cow per hour, so that troughs cope with periods of peak demand.
  • Avoid running black poly pipe along the ground, as water will become very hot.





Milking times

Walking cows to the dairy during the hottest part of the day (about 3pm) adds to their heat loads.

Delaying afternoon milking until 5pm may increase milk yield by up to 1.5 litres per day, regardless of whether the cows are sprinkled with water while in the dairy.

On hot days, be sure to milk and feed cows before 10am. On heat wave days, try to have it done by 9am. Try to offer feed to cows as soon as they exit the dairy. Have the paddock or feed-out area ready and ensure that every cow gets a fair go.