MMM 371 August 7, 1998

Protecting Livestock from Heat Stress
H.D. Hupp, Animal and Veterinary Sciences
P.J. Rathwell, Extension Ag. Economist

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.

SHADE

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.

VENTILATION

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 be stressed.

WATER

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 Handbook.

TEMPERATURE HUMIDITY INDEX (THI)

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:
http://virtual.clemson.edu/groups/psapublishing/DISASTER/drought/Drout2.htm

KEEP AN EYE ON THE ANIMALS

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.

WORKING AND HAULING CATTLE

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 down.

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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