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Heat stress can take toll on cattle herd

Author: Kristy

By Mary Hightower, University of Arkansas Extension

The heat and humidity of an Arkansas summer can take its toll on cattle and increase management tasks for ranchers, said Tom Troxel, associate head-Animal Science for the University of Arkansas System Division of Agriculture.

Cattle generate heat as they digest their food. Cattle use this heat to regulate body temperature to 101 degrees Fahrenheit, plus or minus a degree. When it’s hot, however, cattle do everything possible to dissipate this heat. For calves and older cows, managing heat stress is more difficult.

“Their ability to get rid of heat depends on air temperature, relative humidity, wind, thermal radiation, and the energy level in the ration,” Troxel said. “Since cattle sweat very little, the main ways they cool themselves are through breathing, radiating heat from their bodies, and reducing feed/forage intake. As intake declines, energy needed for performance also declines, whether for milk production in cows or weight gain in growing cattle.”

Shade, water and feed all play a major role in managing heat stress in herds.

Shade is important. Provide shade to pasture cattle during hot weather. Direct sunlight raises body temperature and decreases an animal’s ability to dissipate its own heat. Shade can reduce radiant heat up to 40 percent. Ideally, treed areas used for shade are thick enough to block direct sunlight but sparse enough to allow natural ventilation.

Pasture managers need to recognize that allowing cattle to lounge in shade all summer will, over time, result in ‘nutrient creep’ from the pastures to shade areas and also result in less efficient utilization of pasture.

Water intake is critical. Ambient temperatures in the mid-90s can increase cattle water requirements by 2.5 times compared to 70 degrees Fahrenheit. Water trough capacity and refill rate become very important in this situation. Cattle need 3 inches of water tank space per head during hot weather. If necessary, introduce additional water tanks ahead of a heat wave so cattle can get used to them. Make sure that refill rates are adequate so that cattle intake does not exceed refill capacity. A 1,000-pound animal needs about 1.5 gallons of water per hour during hot weather.

Remember that mature cows nursing calves need 20-30 gallons of water per day during the summer; stocker calves, 10-20 gallons. A rule of thumb in the summer is a gallon of water per pound of daily dry matter intake.

Timing of feeding can make a difference. “There’s not a lot we can do about that with pastured cattle, but if you supplement cattle on pasture, feed toward the evenings,” Troxel said.

If cattle are in a barn, provide adequate ventilation. This may involve opening up all doors and windows, adding fans, or providing access to an outside pen with shade.

Control flies. This involves not only applying repellants and control products, but also eliminating fly breeding areas. Biting flies can cause cattle to bunch up which reduces evaporative cooling via air movement. Fly problems can affect both pasture and feedlot cattle.

Don’t add stress. If at all possible, try to avoid working cattle during extreme heat. Schedule any handling to be done first thing in the morning as daylight allows. Working cattle in the evening is not recommended as cattle are still dissipating heat from the day. Plan major workings, pasture rotations, shipping, etc., in relation to the potential for heat stress.

“A little common sense during our summers can pay large dividends in percent calf crop, weaning weights, and gains,” he said.

To learn more about managing livestock, contact your county agent or visit www.uaex.edu.

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