A string of hot, humid days through much the Plains and Midwest this summer have taken a toll on cattle, according to Kansas State University veterinarian Larry Hollis.

To help cattle producers and feedlot managers determine the risk of such conditions, the University of Nebraska developed a Temperature- Humidity Index. The index is part of a Livestock Weather Hazard Guide, posted on the Ardmore, Okla., website of the Samuel Roberts Noble Foundation: http://www.noble.org/Ag/Livestock/Heat/.

"When there is no daytime wind and/or nighttime temperatures do not drop below 75 degrees so conditions reach a score of 75 (on the Temperature-Humidity Index), producers should be on the alert for heat stress problems," Hollis said. "When the index reaches 79, the situation has reached the danger point. An index of 84 means emergency conditions exist."

Panting scores probably give the best visual method to estimate the severity of heat stress on cattle, he added. If cattle are panting at a rate of 80 to 120 breaths per minute, they are in moderate stress; 120 to160 breaths per minute mark the danger zone; and more than 160 should be considered an emergency.

"When they see signs of moderate heat stress, producers may have a very short time to provide a mechanism for cooling the cattle before the situation becomes life-threatening," the veterinarian said.