Pokey feedlot steers

During a heat stress incident in southwest Iowa on July 11 and 12, 1995, an estimated 3,500-4,000 cattle died of heat stress. A deadly combination of temperatures exceeding 100 degrees, 50% relative humidity and no wind or cloud cover centered over the region. In the Midwest, deadly combinations such as this one are usually short lived but can occur any time from June to August.

Dr. Terry Mader, retired beef specialist at the University of Nebraska, has noted that an incident similar to the one described has occurred somewhere in the central and northern plains states each year from 2009 to 2013. To prevent cattle losses during such heat events, feedlots should implement one or more mitigation strategies.

Shade. After the 1995 incident, ISU beef specialists Darrell Busby and Dan Loy surveyed feedlot managers in the area about which heat stress factors and management practices, and shade was the most effective prevention method. In fact, where cattle were provided access to shade from a building or constructed shed death loss was no different than normal conditions. It is suggested to provide at least 20 square feet of shade when building structures for feedlot cattle.

Water and sprinkling. In the survey, producers also indicated that sprinkling or spraying water on the cattle was effective. Cattle cool by evaporative cooling so intermittent sprinkling is one method. Cattle will also walk in and out of continuous sprinkling. South Dakota State University has evaluated methods of wetting the feedlot surface in the evening to reduce the lot surface temperature.

Signs of heat stress.  As cattle accumulate heat during the day they will show multiple signs of heat stress. Initially cattle will increase respirations as they try to cool themselves by panting. As the heat load increases, cattle will become restless and begin to drool. Even though, at this stage, cattle are spending energy trying to cool themselves they are in danger. With additional increases in the heat load cattle will begin to breathe through their mouth, which is an indication that a heat mitigation strategy should be implemented if it has not been initiated proactively. The last indication is that cattle will protrude their tongue as a last attempt to increase cooling. These cattle are at risk of dying and even if they survive, may take time to recover. Care should be taken to not increase other stresses when trying to cool these cattle.

Feed and water consumption. Expect feed consumption to decrease during periods of heat stress by as much as 20%-40%. In these circumstances, cattle tend to eat more of their feed in the evening so many feedlot managers will adjust feed deliveries to account for this. Water consumption can increase significantly during periods of heat stress so be sure to provide adequate water and drinking space for each animal. Individual animals can consume as much as 15-20 gallons per day during these periods, so be sure to provide at least 1-2 linear inches of drinking space per animal. This may need to be increased to 3 linear inches during severe heat events to provide proper access to water.

Source: Dan Loy, Iowa Beef Center director, and Grant Dewell, ISU Extension beef veterinarian