Managing feedlot cattle to eliminate stress during a heat wave

Jul 25, 2014
by WLJ

Summer heat waves pose a serious danger to cattle in feedlots. Not only is there elevated risk of death loss, but there is also the reduction in performance and efficiency to consider. Developing a plan before hot and humid conditions hit will put producers in a better position to deal with the conditions and minimize the impact on their cattle.

The amount of stress that cattle are under is affected by both the air temperature and the relative humidity, as shown by Figure 1. The combination of high temperatures plus high relative humidity is particularly dangerous, especially when there is little to no nighttime cooling. Solar radiation and air movement aren’t accounted for in this index, but these factors are a major component in determining how high temperatures affect cattle.

Water access is vitally important to maintain the wellbeing of cattle during hot weather. Water consumption at 90° F can by 2.5 times higher compared to intakes at 70° F. The water system needs to have enough capacity so that enough water is available at all times to satisfy cattle demand. There should be at least 3 linear inches of trough access per head. Extra tanks may need to be provided to ensure enough access and holding capacity. Making sure the tanks stay clean will help make sure that water intake isn’t being limited.

Heat stress can also be reduced by using sprinklers to cool both the cattle and ground. It’s important to make sure the droplet size is large enough so that there isn’t a mist created that might only add to the heat stress by increasing humidity. Sprinkling should be introduced to cattle prior to extreme heat and begin before the cattle are under significant heat stress; waiting until the cattle are overheated is too late. An additional supply of emergency water may be needed so that the supply system can meet both sprinkler and drinking water demand.

Another way to mitigate heat stress is by providing shade. Shade will reduce the amount of radiant heat load the cattle would face and reduce the surface temperature of the ground. South Dakota State University (SDSU) Extension has produced a video that shows how shades and temporary water tanks can be utilized on the farm. Providing a layer of light colored bedding also can reduce the temperature of the soil surface in an unshaded pen.

Removing barriers to air movement such as temporary windbreaks or tall vegetation that’s close to the pens will help increase airflow and provide some relief.

When possible, avoid working cattle during heat waves to minimize losses. If it is absolutely necessary to move or work cattle during hot weather, plan on being done before 9 to 10 a.m. The core temperature of cattle peaks about two hours after the peak air temperature and it takes roughly 6 hours for cattle to dissipate their heat load. So even if it cools down at night the carryover effects from earlier in the day could be enough to cause problems if cattle were worked.

Some other management steps to reduce heat stress-related losses include:

• Pay particular attention to cattle that are at higher risk for heat stress. These include heavy cattle, those with dark hides, and those with past health problems.

• Controlling flies will help keep cattle from bunching in a group. That will allow more air flow to each animal.

• Feed 70 percent or more of the daily ration in the late afternoon or evening. Delaying feeding times has been shown to reduce the animal’s peak body temperature.

• One method to determine whether or not to reduce morning feed deliveries is to monitor early morning respiration rates. If cattle are still breathing faster at 6 or 7 a.m., that’s an indication that the heat load didn’t dissipate overnight and offering less feed and sprinkling more often would be warranted.

• Feeding melengestrol acetate—MGA—to heifers has been associated with less death loss due to heat stress, presumably because of less riding activity. Other resources that are available to help producers manage through a heat wave include the USDA Heat Stress Forecast Maps ( ?docid=19899&viewDay=7), the SDSU Climate and Weather page, as well as additional materials related to heat stress in cattle found on iGrow Beef. — Warren Rusche, Cow/Calf Field Specialist, iGrow Home Livestock Beef