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Brenda Ekwurzel, Ph.D.

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Taking Stock of the Summer of Extremes: 2011

Posted: 10/12/11 04:06 PM ET

Unbearable heat and humidity over six days in late July caused considerable losses of livestock on farms in Iowa, Minnesota, and South Dakota. Heat indexes soared, with temperatures in some parts of the region feeling like 120 degrees -- and even as high as 131 degrees in Iowa.

On a Tuesday afternoon in the middle of the heat wave, water tankers from two Minnesota fire departments rushed to provide cooling water to Joe Nelson's livestock farm on the Minnesota-Iowa border. Despite emergency efforts, 100 of his cattle died. Nelson wasn't alone in his massive losses. One Minnesota farm lost 150 cattle -- another, more than 300.

Temperatures across Iowa averaged 79 degrees F in July, five degrees higher than average, according to Iowa state climatologist Harry Hillaker. The average heat index - a way of expressing how hot it feels after humidity is factored in -- for the state officially was 110 degrees or higher on six days.

During the scorcher, farmers brought extra water to livestock and rescheduled feeding times to cooler times of the day, but the extreme weather proved lethal. More than 4,000 cattle died in Iowa, an estimated 1,500 in Minnesota, and 1,500 in neighboring South Dakota.

Estimates put those losses at $10 million to $13 million. "It is a huge financial loss," said a University of Minnesota beef extension educator, Grant Crawford. "Many of the cattle that died were near market weight. For the cattle that were nearly market-ready, they probably weighed 1,200 to 1,300 pounds and were worth around $1,400 per head." Some farmers qualified for federal aid under the U.S. Department of Agriculture's Livestock Indemnity Program, part of the Food, Conservation and Energy Act of 2008. Reimbursements are based on 75 percent of fair market value.

Two factors contributed to the animals' severe heat stress: the prolonged, extremely high daytime heat index and unusually warm nighttime temperatures. The high heat index was the result of air temperatures of 97 to 100 degrees during a period of high humidity. Hillaker said the humidity rises because of "the area's relatively deep, rich soil, which can store a large amount of water compared to what is typically seen across southern states. Thus, when temperatures warm, the vegetation can work from a huge store of moisture and thus add a large quantity of local moisture into the atmosphere via transpiration, in addition to what is transported here from the Gulf of Mexico by prevailing southerly winds."

Instead of cooling down at night, temperatures remained high. In Iowa, minimum nighttime temperatures have been rising more than daytime temperatures since 1970, a trend that is expected to continue.

Those high nighttime temperatures proved to be the tipping point for the cows' survival. Grant Dewell, a beef extension veterinarian at Iowa State University, said, "If nighttime temperatures do not drop below 70 degrees at night, cattle are not able to dissipate all the heat they accumulate in the day, so they end up bringing some of that heat load into the next day. Typically, we see losses starting on the third day of a heat event because cattle have accumulated excessive heat loads."

Dewell said he was surprised that most of the losses were not in southwestern Iowa, the hottest area of the state. He was also surprised by the number of losses reported, despite widespread news warnings to make livestock farmers aware of the risks. "We believe that cattle producers in southern Iowa responded to the warnings and took appropriate measures because they are used to dealing with heat events," he said. "However, producers in northern Iowa and probably Minnesota do not typically see these heat events extend that far north and probably did not take any measures to protect their cattle."

For the surviving herds, heat stress led directly to reduced milk production, less weight gain, and lowered reproduction, Dewell said. Farmers won't know about their reproductive losses until next spring, after calving. While some producers will give pregnancy tests to their cattle this fall, many will not, and researchers won't have any estimates until the spring. "I expect that reproductive losses will be significant," Dewell said. "Producers that artificially inseminate cattle had difficulty getting cattle bred in July because of the heat, and we will definitely see similar results for the bull-bred herds. I would not be surprised to see fertility decreased by 10 to 20 percent for cows that should have been bred in July."

Some farmers are helping their livestock adapt to extreme heat by installing monoslope buildings -- open-sided structures with an angled roof that can reduce temperatures by 10 to 20 degrees and allow better survival rates. Grant Dewell said the buildings offer two features that help cool cattle. "One is a roof that provides shade -- probably the biggest effect and one that would be true for any shade structure," he said. "The other thing they do is, if they are designed right, they can increase air movement. As air heats up, it will rise up, move up the slope of the ceiling and then move out the front of the building. This will pull air into the back of the building and increase the air flow."

Just as a black T-shirt absorbs more heat than a white T-shirt on a sunny day, the temperature of the cows' black coats was strikingly different in sun versus shade. One day at noon during the heat wave, on a farm near the town of Nevada, Iowa, the president of Iowa Beef Systems, Bill Rubis, observed an infrared thermometer that measures the coat temperatures of cattle exposed to sunlight and those in shade. The thermometer registered 140 degrees F on cattle in open air and 106 degrees on coats shaded under a monoslope structure. Rubis said a typical monoslope barn housing 500 head of cattle costs $500,000 to build.

"The problem with building a specific type of building is it may be difficult to justify the added cost of this type of facility to prepare for a heat event that may only happen once every year," said Crawford. "I know of Minnesota open lots that made it through the heat with few or no deaths. It is really all about preparation, though the covered buildings such as monoslopes do provide peace of mind for when extreme weather occurs."

Perhaps there is a lesson in the apparent difference between livestock deaths in southwestern Iowa, where farmers are used to planning for extreme heat, and in northern Iowa, where producers were unprepared for it: it's less costly to prepare for climate change, which has already increased the chances for extreme heat wave conditions, than to suffer the kinds of losses that economists call the "costs of inaction."