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Reduce heat stress in cattle

With temperatures expected to reach dangerous highs this
week in the middle of the country, Iowa State University (ISU) Extension beef
veterinarian Grant Dewell urges beef cattle producers to prepare for these
weather conditions to maintain herd health.


Facts you
should know

  • Feedlot cattle are at higher risk than pastured
    cattle, which have the ability to seek shade and avoid radiant heat from dirt
    or concrete surfaces.
  • Temperatures exceeding 80 degrees F cause physiologic
    stress on cattle. Though they are not at risk of dying, their health can
    deteriorate.

  • Compared to other animals, cattle cannot dissipate
    their heat load effectively due to their inability to sweat.

  • Cattle’s core temperature peaks 2 hours after peak
    environmental temperature.

  • It takes at least 6 hours for cattle to dissipate
    their heat load.
  • Black cattle and heavy cattle and respiratory
    compromised cattle have an increased risk of heat stress, and higher chances of
    death


Managing
the heat



Careful monitoring:

Don’t
work cattle at all in high heat. Finish working cattle before 9 to 10 a.m.
during the summer. Do not work cattle in the evenings after it has cooled
off.  It takes at least 6 hours for
cattle to recover from their heat load. 
Cattle should not wait in processing areas longer than 30 minutes.


Water
requirements:

Cattle lose water more quickly from increased respiration
and perspiration when it’s hot. 
Consuming water is the only way cattle can reduce core body
temperature.  Cattle need 3 inches
of linear water space per head during the summer.  The supply should be able to deliver 1.1% of body weight of
the cattle per hour.  A 1,000-pound
animal needs about 1.5 gallons of water per hour. Introducing extra water tanks
before extreme heat will allow cattle to become accustomed to them.


Feeding
changes:

Cattle should not be fed in the morning when body heat will
peak when environmental temperatures are also at their highest (midday).  Cattle should receive at least 70% of
their feed 2 to 4 hours after the day’s peak temperatures.  Changing the ration is controversial,
but the general recommendation is to reduce the diet energy content of feed by
5 to 7%.


Shade and
ventilation:

There should be 20 to 40 square feet of shade per
animal.  Shade structures are most
adequate when they have an east-west orientation and are more than 8 feet off
the ground to heighten air movement. 
Removing tall vegetation within 150 feet of the feedlot pens will also
expose cattle to more air movement.


Cooling
techniques:

Sprinklers can cool cattle during times of stress by
increasing evaporative cooling and reducing ground temperature.  Sprinklers are adequate when they wet
the animal and not just mist the air. 
Sprinklers should not interfere with drinking water supply.  Use sprinklers intermittently to avoid
mud and increased humidity.  Assess
water temperature: thermal shock from too cold of water can kill cattle that
are extremely stressed.  Once
sprinklers are utilized, they should be continued until the heat is over.

Fly control will also reduce cattle stress.  Biting flies cause cattle to bunch up,
decreasing cooling.  Minimize
breeding areas for flies and apply insecticides to decrease fly populations
before heat stress.
 

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