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How to survive the dog days

Agriculture.com Staff 08/01/2008 @ 9:14am

Cattle are not well equipped to handle the high temperatures and humidity typical of mid- to late summer.

The comfort zone varies by age and type of animal, says University of Nebraska veterinary and biomedical sciences professor David Smith. Calves are comfortable between 45 and 80 degrees Fahrenheit, Smith says, while feeder cattle are better off between 0 and 75 degrees. Dairy cattle are comfortable between 25 and 65 degrees. Cattle on higher-energy diets are within their comfort level up to 90 degrees.

"Conditions most conducive to heat stress in beef and dairy cattle are prolonged high temperatures with above-average humidity, below-average winds, and when cattle have had little time to adapt to the heat load," Smith says. "Fat cattle, new arrivals, cattle with dark hides, recently fresh dairy cattle, and cattle with illnesses are the most susceptible to heat stress."

Stressed cattle will often require up to 50% more water intake to control body temperature. Water temperature is also key, according to Ohio State University Extension beef specialist Stephen Boyles.

"Water temperature affects rumen temperature and, thus, blood temperature, which affects brain centers that control feed consumption," Boyles says. "Temperature increases from 70 to 95 degrees can increase total water requirements by about two and a half times."

Shade is another way to combat potential heat stress in cattle. Virginia Tech University Extension dairy scientists Gerald Jones and Charles Stallings recommend providing artificial shades that allow maximum airflow.

"To achieve the most benefit from the shade structure, feed and water must be available to the cows under the shade," they say.

High-energy or hot rations help control body heat by providing more concentrated protein feed than those with more roughage, which can raise rumen fermentation temperatures during digestion.

"Cattle actually produce less heat when consuming corn than when consuming hay," Boyles says.

And with increased water consumption, cattle will excrete more urine, thereby losing more minerals. Boyles says trace mineral salt should be made available to cattle in a shaded area.

"Loose salt will be more readily consumed than block salt," he adds.

Cattle are not well equipped to handle the high temperatures and humidity typical of mid- to late summer.

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