Risk to Livestock during Heat Waves

Cattle deaths have been mounting in the central U.S. as the recent heat wave has pushed heat indices above 120 degrees in a number of states. Faced with dry pastures, rapidly depleting hay supplies and drought stressed surface water sources, ranchers in Texas are engaging in a significant  livestock sell-off, referred to in one press account as culling into “the heart of the herd.” The size of the U.S. herd is now at a record low as farmers liquidate, enticed by high beef prices and expensive feed. The situation is dire enough that the government has stepped in with low interest loans to ranchers and direct payments for farmers that lost animals due to the extreme weather. Under the Livestock Indemnity Program, cattle lost to extreme weather are reimbursed by the government at 75 percent of their value, a significant expenditure when cattle losses are counted in the thousands. Texans are already looking for ways to adapt to the drought and improve their climate resilience. Henderson County is hosting a training session on August 22 entitled “Managing the Effects of Drought for Beef Producers.”

In the Northern Plains states, where flooding has dominated instead of drought, a high-humidity heat wave has killed several thousand head of cattle. While data on the exact numbers of heat-related cattle losses are difficult to come by, it is clear that losses were larger than usual this year, with initial reports of about 2,500 head lost in South Dakota and Minnesota and an additional 4,000 head lost in Iowa. Although these deaths represent a small percentage of the overall heard they demonstrate the risk from extreme heat.

The recent spate of heat, humidity and drought in the plains states show how vulnerable herds are to climate change. The risk of more extreme weather events that cause widespread hardship among ranchers is only increasing and the Great Plains is among the regions at the highest risk of extreme heat over the next century. During the climate of the recent past, (Figure 1), 100°F days were rare. However, projections show that by the end of this century, current cattle producing regions could average 75 to 120 days per year where the temperature exceeds 100°F  (Figures 2 and 3). In addition, these temperature projections do not address the expected increase in humidity–think of the heat index that weather forecasters mention on the nightly news–which adds additional stress to livestock (as well as people). Since livestock are sensitive to extreme heat and cattle cannot be raised indoors in large numbers, continued warming of the climate is likely to pose a serious risk to American ranchers.

The U.S. Global Change Research Program warned about the risks of climate change to livestock in a recent report: “Milk production declines in dairy operations, the number of days it takes for cows to reach their target weight grows longer in meat operations, conception rate in cattle falls, and in swine growth rates decline due to heat. As a result, swine, beef, and milk production are all projected to decline in a warmer world.” These negative impacts occur at a temperature humidity index (THI) of 80 or more, and at a THI of 98, cow deaths can occur. The recent heat wave resulted in THI values around 90 in the Northern Plains and Midwest for several days.

Fortunately, there are measures that can be taken to reduce the impact of heat on cattle. Heat tolerance is considered to be one of the most important traits in selective breeding programs and certain popular breeds from tropical regions show great promise in tolerating extreme heat. In addition to breeding tolerance, other adaptations can work to directly cool existing stocks. Ensuring cows are not overcrowded, have adequate access to shade or mist sprayers, and have easy access to water, although difficult in the midst of drought like the current one in Texas, can help prevent severe heat impacts. Changing a herd’s diet by adding vitamins and fat while decreasing protein intake may also help to reduce the effects of extreme heat, and ensuring cows have access to quality feed can increase resilience.

Future cattle ranching is likely to require a wide variety of adaptations both through selective breeding and direct cooling efforts. Learning about vulnerability to extreme heat from events today and accurately assessing the risk level into the future are keys to ensuring that the U.S. livestock industry remains as healthy and productive for future generations as it has been for generations past. But the necessary measures will come with a cost and the more the climate warms, the more expensive the necessary adaptation measures will be.

Dan Huber is Science & Policy Fellow