How to Identify and Manage Heat Stress in Your Herd

There is no question that heat stress can negatively impact animal performance.

Kimberly Kester, University of Wisconsin-Madison dairy and livestock program manager, says cattle have a comfort zone of 32 to 77 degrees Fahrenheit.

“When temperatures rise above this range, cattle use valuable energy to stay cool,” she explains. “Environmental factors contribute to heat stress in cattle, including ambient temperature, humidity, wind speed and solar radiation.”

“For feedlot cattle heat stress reduces daily gains, negatively impacts feed efficiency and can lower dressing percent,” says Bill Halfman, University of Wisconsin-Madison state beef outreach specialist, in a recent Wisconsin Cattlemen’s Cattle Trail newsletter. “Cow-calf producers could expect greater embryonic loss in the first few weeks after conception due to heat stress. High temperatures could also impact semen quality in bulls two to four weeks after the heat stress event, resulting in lower conception rates. Prolonged exposure to heat stress is much more detrimental than short-term heat stress and its effects linger long after temperatures drop back below the heat stress threshold.”

The following chart shows the level of heat stress on beef cattle at different temperature and humidity levels.

(University of Wisconsin-Madison)

To evaluate cattle heat stress, Halfman suggests counting breathing rate.

“Since cattle do not sweat, they try to dissipate heat by increasing their breathing rate,” he explains.

The following chart shows the level of heat stress based on breathing rate.

(Brown-Brandl et al., 2005)

Kester says other signs of heat stress include spending more time standing, restlessness and drooling.

“In extreme cases, cattle may open-mouth breathe and breathing appears labored,” she says. “Young calves and heavy cattle are more sensitive to heat and have a greater risk of heat stress.”

Halfman suggests producers follow these five management practices to help reduce cattle heat stress:

1. Avoid handling, transporting, moving or processing cattle. If these activities must occur during this time, they should be done early in the morning hours while using low-stress handling techniques, but it is best to delay them until better weather when possible.
2. Provide plenty of water. Make sure the water supply to cattle is able to meet the increased demands during hot weather. Also, make sure the waterers are clean to not discourage intake. It may be necessary to provide additional tanks especially if cattle only have access to one tank in the pastures. Kester adds that on an 80-degree day, a 500-lb growing calf needs roughly 8 gallons of water per day, and a lactating cow needs up to 18 gallons.
3. Provide shade. Shade is critical, especially for dark-haired cattle and/or fleshy cattle; therefore providing a pasture with access to trees or open buildings. Portable shade options are also a possibility. In open feedlots or pastures without shade, please see Tip 4 to reduce heat stress. It is also a good idea to provide shade in such a manner to prevent bunching up, which reduces good airflow and often causes a mud hole under the shade. Beef cows should have access to about 30 square feet of shade per head.
4. Sprinkle cattle and pen with water. As evening approaches cattle try to dissipate heat, so spraying water on mounds or pens where cattle can lie down will help. Also avoid spraying cattle with a mist, because in high humidity this may only contribute to instead of alleviating the problem of heat stress. Be careful and first introduce the water to cattle in early morning hours or ahead of time so they are accustomed to being wetted down to avoid adding additional stress to the cattle when spraying them with water.
5. Provide adequate ventilation. If cattle are being fed and housed in an enclosed barn or building, use fans to move air out and through the building; open sides of the barn to improve airflow, or provide access to an outside pen or pasture with shade. Using sprinklers in this situation will potentially intensify the problem and create more humidity without proper air movement to remove it from the building. Keep in mind that some sheds may have dead air spaces in them, for example in the back, below the knee wall where cattle may lay down. Fans and positive pressure tubes can help correct these problems.

Kester also suggests avoiding feeding during the hottest parts of the day, because body temperatures increase as feed is digested.

“Monitoring your herd’s behavior, providing access to shade and water, and making minor changes to management strategies can reduce the risk of heat stress in cattle,” Kester summarizes. “This will have a positive impact on animal welfare and your bottom line.”

For more details, including heat stress prediction maps, visit the U.S. Meat Animal Research Center website or download the Keep Cattle Cool and Comfortable in Summer fact sheet.