They look content, placidly grazing across a pasture or steadily crunching corn in dusty feed lots across the Central Plains, but if it's the middle of summer, cattle are well aware that the sun is blazing and the heat can be brutal.

Just like their human counterparts, cows don't need a weatherman to know when it's too hot. Most are sweating through extreme temperatures, much like their owners, looking for a cool spot in the shade to relieve heat stress.

Individual cows react differently to heat, but in the worst cases, livestock suffering from heat stress can lose their appetite or experience reduced rates of growth, making them more susceptible to illness or even death.

It might seem overly obvious to say that cattle need some kind of shade for protection from dangerous conditions, but a group of Agricultural Research Service researchers wondered precisely how much shade is needed and what types of sun shelters would best meet the needs of animals and improve the bottom line for livestock producers.

The scientists' work has three main components: analyzing animal susceptibility to heat stress, 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. This is significant because cattle, like humans, sweat to keep cool. Results showed that coat color, wind speed, access to shade, and breed could influence an animal's physical response to heat.

For example, the scientists observed that Angus cattle adapted to conditions in Kansas had higher body temperatures than those adapted to conditions in Florida. Though genetically similar, the Kansas cattle also had a more erratic sweating rate, suggesting that 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 agency's Roman L. Hruska U.S. Meat Animal Research Center (USMARC) in Clay Center, Neb., 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.

The result was a heat stress model that incorporates predictions of temperature, humidity, sun intensity and wind speed. The model predicts when environmental conditions are particularly likely to cause heat stress, and presents the information in an easy-to-read, color-coded map that includes South Dakota, Nebraska, Iowa, western Colorado, Kansas, Missouri, Oklahoma, and northern Texas.

Having more information about the potential benefits and disadvantages of stress-alleviation methods can help managers decide how to respond to dangerous heat situations, so the USMARC scientists have evaluated one of the more common management options, comparing the effectiveness of four commercially available shade materials to protect cattle raised in outdoor pens.

They found that 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, providing some shade but allowing sunlight to still filter through, while shades made of solar radiation-blocking polyethylene cloth offered the most protection.

Still, all the shades offered some protection that could result in slower respiration rates and lower body temperatures — even the snow fence, which is less expensive than the other shades.

"Based on these results, we can conclude that erecting shades is indeed an effective method to reduce stress-related losses," Brown-Brandl says.

Research efforts like these have been essential for developing tools and management practices to help cattle producers beat the heat. And that's a relief not just for the cattle, but for the people who work with them as well.

Tami Brown Brandl, Roger Eigenberg and John Nienaber all work at the USDA-ARS Roman L. Hruska U.S. Meat Animal Research Center in Clay Center, Neb.

For more information about this research, contact Mark Boggess, leader of ARS National Program #101, Food Animal Production.