Cattle should be closely monitored for signs of heat stress during this week’s hot, humid weather, says Ben Holland, South Dakota State University Extension beef feedlot specialist.

Symptoms of heat stress range from mild to severe as conditions worsen, says Holland. Initially, animals will increase their respiratory rate in an attempt to cool themselves. Increased salivation and open-mouth breathing will commence, and in severe cases of heat stroke, animals will become uncoordinated, weak, and go down and not be able to rise. When these latter symptoms hit, recovery is unlikely.

Some animals will likely be more severely affected than others. Producers should pay close attention to dark-hided animals, fleshy animals, or animals with histories of respiratory disease.

Heat-stress symptoms peak in the early evening hours after the animal's body attempts to regulate its temperature and fails. "The most important thing is to be prepared to take steps to intervene before severe signs of heat stress manifest themselves," he says.

Cattle in feedlots are generally the most impacted in high heat conditions, and steps should be taken to allow them to adequately dissipate heat. During hot summer days, they accumulate internal heat, which must be released during the nighttime. When nighttime low temperatures are above 70° F, especially for extended periods, heat removal is not very affective.

"The most important thing cattle feeders can do to help cattle cool off at night is by sprinkling mounds in dirt pens late in the evening or at night,” says Holland. “This provides a cool place for cattle to lay down, allowing the heat to dissipate. Cattle can be sprayed directly during the day as well, but if cattle are sprayed, large water droplets should be used. Too fine a mist will only add humidity and make problems worse."