July 12, 2000 | By: Aimee D. Heald

Kentucky is entering the hottest, most humid time of the year. All this heat can be stressful for beef and dairy cattle.

The normal body temperature for cattle is about 101.3 degrees Fahrenheit. But many things, such as humidity, solar radiation and wind velocity interact with the air temperature and all that affects an animal's ability to maintain a steady temperature.

Larry Turner, chairman of the University of Kentucky College of Agriculture's biosystems and agricultural engineering department said recent studies by UK researchers have shown that shade can help cattle maintain a healthy body temperature.

In the study, researchers draped portable 12 X 24 ft. pipe-constructed frames with shade cloth in pastures with cow/calf pairs and stocker steers. Each cow wore a data logger to gather accumulated ambient air temperature and body temperature measurements. Ear probes were used to measure body temperature. Also, researchers weighed cattle at 28-day intervals.

Turner said the data indicated that shade may lower the body temperature of beef cattle by .5 to 1.4 degrees Fahrenheit. The cattle in the study gained more weight per day when they had access to shade. The study was conducted by the biosystems and agricultural engineering department in cooperation with Brian Larson, beef specialist, and other personnel from the UK animal science department.

Shade is even more important to cattle on dirty fescue, as these cattle can't regulate body temperature as well.

Dairy Specialist, Donna Amaral-Phillips said that all cows respond to heat stress by eating less and by drinking more water. "Cows which are heat stressed produce less milk and have lower conception rates," she said. "Studies have shown that the maximum decrease in production usually is seen 24 to 48 hours after exposure."

When the nighttime temperatures drop to allow the dairy cow's core body temperature to cool down, the cow can more readily handle daytime heat stress. Dry cows and heifers also are subject to heat stress. Bringing cows within three weeks of calving into the holding pen and cooling them can be beneficial and may improve production after calving. Cows who endure heat stress during their last trimester of pregnancy have smaller calves and may produce less milk in the next lactation.

Amaral-Phillips agrees that cows need shade to cope with the hot temperatures and high humidity of summer.

"Trees are the best natural shade," she added. "However, if trees are the only source of shade, cattle need to be rotated every couple of days to prevent mastitis."

Fans and sprinklers can also provide some relief and protection from heat stress by wetting the animal to the skin. The fans should be located near the feed bunk and in the holding area. Recent studies have shown that fans and evaporative cooling systems over freestalls can improve cow comfort and milk production.

Amaral-Phillips recommends altering feeding practices to fit summer conditions. Since cows usually eat less in the hot, summer months, rations need to be reformulated to account for the lower intake. Another good idea is to feed rations during the cooler parts of the day.

Amaral-Phillips and Turner agree that water is critical to preventing heat stress. Not only having enough cool water, but also an adequate reserve so many cows can drink at once. Turner said future shade studies are planned and will take place at multiple shade levels. Studies like these are important since extended periods of extreme heat can hinder cattle productivity, health and well-being.

Additional information, shade structure plans, and publications are available through your local Cooperative Extension Service office.


Larry Turner 859-257-3000, Donna Amaral Phillips 859-257-7542, Bryan Larson 859-257-2892