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Warning: Heat Stress, Beef Cows

28 June 2018

The bovine thermal comfort zone is -13oC to +25oC.  Above this upper level, cattle will start to suffer some degree of heat stress.  Cattle naturally minimise exertion to stay cool.  High temperatures will also have some effect on sperm quality and even embryo viability – each of these being hugely important in the middle of the main beef-breeding season.

High humidity and temperature levels, especially if it is a very still day, can reduce feed intakes and therefore milk yield or growth rates whilst suppressing immunity and increasing mastitis risk.  Any impact on milk yield is more important in high yielding dairy cows but do not forget beef dry cows near calving.  These summer calvers will already have low dry matter intakes and rapid weight loss so risk having poor energy for calving, and with dropping grass availability and quality in front of them, could affect colostrum levels for the calf and her ability to regain condition in preparation for bulling.  A 10% reduction in feed intake is a sign of high heat stress levels, although not easily assessed at grazing.

The most visible symptoms of heat stress tend to be elevated breathing rates:

In all stock:

  • Clean drinking water is essential as voluntary water intakes can increase by 20% in hot weather, particularly in newly calved cows.
  • Avoid walking stock in the hottest part of the day
  • As grass growth slows, some youngstock will quickly take to creep feeders so this should be introduced slowly to avoid sub-clinical acidosis.

 In housed stock:

  • Improve airflow and ventilation, which might include replacing shed doors with gates.
  • Avoid overcrowding in sheds
  • Gradually change feeding times to early morning or late evenings to promote feed intakes and minimise feed spoilage.

Written by Robert Logan, for further information contact robert.ramsay@sac.co.uk 

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