Published: July 08, 2009 08:55 am      

Heat stresses everyone, everything -- including cows

STILLWATER -– Understanding and avoiding heat stress in cattle can be a valuable management tool in Oklahoma, where most areas of the state experience 70 or more days each year with temperatures that exceed 90 degrees Fahrenheit.

“Cattle have an upper critical temperature that is approximately 20 degrees Fahrenheit cooler than humans,” said Glenn Selk, Oklahoma State University Cooperative Extension livestock specialist. “When we’re uncomfortable at 80 degrees and feel hot at 90 degrees, cattle may well be in the danger zone for extreme heat stress.”

The potentially bad news does not end there. Humidity is an additional stress that intensifies ambient temperature problems by making body heat dissipation more difficult. In other words, it can be tough to cool off in Oklahoma during the summer, for people and cattle.

High humidity contributes to the likelihood of heat stroke or prostration because water evaporation from the oral and nasal cavities is decreased, in spite of rapid panting, a heat regulatory device in cattle.

“Panting often occurs at rectal temperatures at or above 104 degrees Fahrenheit, but may begin at even lower body temperatures,” Selk said.

Signs of overheating in cattle may develop suddenly and depend on the environmental conditions and health of the animal. Some overheated cattle manifest restlessness, excitement and muscle spasms. Others may be dull and depressed. A protruding tongue may be covered with saliva, and frothy mucus may be discharged at the nostrils.

Fortunately, overheating in cattle can be prevented under most management conditions. Allowing cattle access to cool water and mineral supplements is a must during hot summertime weather. Access to shade and air circulation should be provided if at all possible. Nathan Anderson, Payne County Extension director and agricultural educator, reminds producers that it is a good idea to work cattle before 8 a.m. during hot weather, and all cattle work should be completed by 10 a.m.

“While it may seem to make sense to work cattle after sundown, they may need at least six hours of night cooling before enough heat is dissipated to enable them to cool down from an hot day,” he said.

Cattle that must be handled during hot weather should spend less than 30 minutes in the working facility, according to OSU recommendations. Drylot pens and corrals loaded with cattle will have little if any air circulation.

“Cattle will gain heat constantly when in these areas,” Anderson said. “By limiting the cattle’s time in a working facility, the producer can help limit the animal’s heat gain and therefore the heat stress.”

The most basic rule is to make every effort to provide cattle access to cool, fresh water, especially for animals that are in close, confined areas for any length of time.

“During hot weather, cattle will drink more than 1 percent of their body weight per hour,” Anderson said. “Producers need to be certain that water supply lines are capable of keeping up with demand when working cattle during hot weather.”

Excitable cattle will be even more prone to heat stress if handled at high environmental temperatures.

“If animals are going to have limited access to water under stressful conditions such as shipping by truck or trailer, they should be allowed water prior to further stressful situations,” Anderson said.

Anderson and Selk point out that it is fortunate most cattle handling for health and production purposes in Oklahoma occurs in the relatively cooler weather of spring and fall.



resulting in only an occasional need for cattle handling in the heat of summer.