Recent cooler weather has helped the situation, but state officials in Kansas say high heat and humidity killed more than 2,600 cattle July 16-18 in feedlots located in a line from Salina to Dodge City.

To help cattle producers and feedlot managers determine the risk of such conditions, the University of Nebraska has developed a Temperature- Humidity Index (THI). It’s part of a Livestock Weather Hazard Guide posted on the Samuel Roberts Noble Foundation website at www.noble.org/Ag/Livestock/Heat/.

"When there’s no daytime wind and/or nighttime temps don’t drop below 75° so conditions reach a score of 75 on the THI, producers should be on the alert for heat stress problems," Larry Hollis, Kansas State University DVM, tells Southwest Farm Press. "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 adds. If cattle are panting at a rate of 80-120 breaths/minute, they’re in moderate stress; 120-160 breaths/minute are in the danger zone; and more than 160 is 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," Hollis says.

Meanwhile, a group of USDA Agricultural Research Service (ARS) researchers set out to determine how much shade cattle need and what types of sun shelters are most effective. The scientists began by analyzing animal susceptibility to heat stress, then identifying contributing environmental factors, and evaluating management techniques to combat the stress.

One study analyzed several factors that influence the sweating rate in different breeds of cattle. Like humans, cattle sweat to keep cool, and results showed that coat color, wind speed, access to shade, and breed all influence an animal's physical response to heat.

For example, researchers found that Angus cattle adapted to conditions in Kansas had higher body temps than those adapted to conditions in Florida. Though genetically similar, the Kansas cattle also had a more erratic sweating rate, suggesting the Florida cattle are better suited to warmer climates.

To create a more accurate model, ARS scientists Roger Eigenberg and Tami Brown-Brandl at the U.S. Meat Animal Research Center (USMARC) in Clay Center, NE, worked with engineer John Nienaber to analyze weather data from significant heat waves and identify environmental factors that contributed to higher incidences of cattle stress.

Their resulting heat-stress model incorporates predictions of temperature, humidity, sun intensity and wind speed. The model predicts when conditions are particularly likely to cause heat stress, and presents the info in a color-coded map that includes South Dakota, Nebraska, Iowa, western Colorado, Kansas, Missouri, Oklahoma and northern Texas. View it at www.ars.usda.gov/Main/docs.htm?docid=20426

The USMARC scientists then compared the effectiveness of four commercially available shade materials to protect cattle in outdoor pens. They found all the materials reduced cattle stress, and the higher the percentage of solar radiation blocked by the shades, the more effective they were at reducing stress. Porous snow fence material was the least effective (and cheapest), but shades made of solar radiation-blocking polyethylene cloth offered the most protection.

For more detail on his work, go to www.ars.usda.gov/is/np/ha/han42.htm