|MMM 371||August 7, 1998|
When humidity and temperatures climb, keep a close eye on beef cattle. Temperatures in the 80's and 90's coupled with high humidity can cause heat stress. This stress causes general discomfort, decline in animal performance and even death. Heat stress is defined as any combination of temperature, humidity, radiation and wind producing conditions higher than the animals thermal neutral zone. Beef cattle cool themselves primarily through breathing. They sweat only about 10 percent of what humans do.
Keep the cattle out of the sun from about 9:00 a.m. to 4:00
p.m. Light haired animals (Charolais, blonde Simmentals and crosses)
can even get sunburn. Angus and black animals can be easily overheated
by radiant heat because the black absorbs more of the sun's radiant
heat. Either open-sided sheds, trees, or other shade can reduce
the radiant heat by as much as 40 percent.
Have the shade in a location where there is a breeze and ensure
that the sides are open for good ventilation. The shed roofs should
be at least 10 feet tall. If the peak is open it will allow the
hotter air to escape. If the roof is insulated, it will help reduce
the radiant heat. Without proper ventilation in buildings and
shaded areas, heat and moisture accumulate and the animals will
Clean, fresh and preferably cool drinking water in good supply
is vital to beef cattle in hot humid weather. Beef cattle cool
themselves by panting and some sweating. In panting, there is
water loss from the lungs. Since beef animals do not sweat, in
extreme heat, they may need to be sprayed with water to keep them
cool. Check the water troughs daily to make sure there are no
supply problems. Make sure there is enough space for everyone
to drink, but not so much that the water grows warm and stale
throughout the day. You want the water supply to turn over rapidly
and be cool and fresh. For more information, see "Water for
Beef Cattle," Section 2002 in the Southern Region Beef Management
The temperature humidity index (THI) is used as a guide to measure heat stress.
THI combines the effects of temperature and humidity into one value. There are
three stress categories (temperatures given in Fahrenheit): Livestock alert
is 75-78 degrees, Livestock danger is 79-83 degrees, and Livestock emergency
is 84+ degrees. At 40% relative humidity (RH) the three levels are at 84 degrees,
90 degrees and 98 degrees, respectively. For 60% RH the three levels are 80
degrees, 84 degrees and 92 degrees, respectively. At 90% RH the three levels
are 76 degrees, 80 degrees, and 86 degrees, respectively. The higher the humidity
the lower the temperature for the Livestock alert, danger and emergency levels
to occur. For more information on the temperature humidity index go to the web:
If heat stress is a big concern, keep
checking the cattle. Temperatures above 104 degrees F are getting
dangerous. Temperatures in excess of 107 degrees F are at the
critical stage and can lead to possible heart failure.
Do not work the cattle through chutes
or move them from pasture to pasture during the heat of the day.
If you have to move or work cattle do it before 9:00 a.m. or after
5:00 p.m. or later. This is at the time of the day with the least
solar radiation, making it cooler. If cattle become over heated
and start panting, stop working or moving them and let them cool
Also, when you haul cattle, do it in early morning or late afternoon or early evening to reduce heat stress. Plan on hauling fewer animals per load, which will reduce the heat production in the trailer. Plan your trips so the animals can be loaded immediately before leaving and unloaded immediately on arrival. There is limited ventilation and poor cooling, if cattle have to stay on a still trailer for an extended period of time.
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