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Helping cows cope with heat stress

Sector News Sector News19-6-2018

For a cow to achieve optimum performance, their ambient temperature should be between 5°C and 25°C. 

There will be some variation, according to breed, weight and feeding levels, but this is a useful target temperature range to keep in mind. If cows are left exposed to temperatures in excess of 25°C for prolonged periods of time, heat stress occurs and cows will start cooling themselves down by panting, drooling and increasing internal blood flow. 

Afbeelding: Cows at water trough Jonos

Effects of heat stress

All of these actions use energy and nutrients that would normally be utilised by the cow. The effects of heat stress can be seen by:

  • Lower milk yield
  • Decreased butterfat
  • Fertility issues
  • Rumen health problems

It is important to remember that cows already generate a high volume of heat, so it does not take a large increase in ambient temperature for cows to start suffering from heat stress. The temperature humidity index (THI) is a good indicator of potential heat stress problems. 

Heat stress identification

The use of a hygro-thermometer or local temperature and humidity data will help you make heat stress decisions. 

Afbeelding: heat stress table

Impact of heat stress on animals

Milking cows

  • Reduced conception and pregnancy rate due to embryo survival - (energy)
  • Reduced rumen pH (acidosis) due to sodium bicarbonate losses when drooling/panting
  • Milk yield loss due to reduced dry matter intake and energy availability
  • Lower milk quality (butterfat) due to rumen health and decreased fibre digestibility

Dry/Transition cows

  • Increased health issues (mastitis) due to additional immune stress
  • Reduced foetal metabolism and growth rates
  • Reduced rumen pH and metabolic acidosis risk, especially on full DCAB systems
  • Further decrease in dry matter intake in the close-up period


  • Heifers can miss first calving targets of 22-24 months of age due to negative impact that heat stress has on fertility, feed intakes and growth
  • Calves can also experience lower dry feed and milk replacer intakes reducing growth rates

Solutions for heat stress

Afbeelding: heat stress solutions 2