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College of Food, Agricultural, and Environmental Sciences


Heat Stress Costs U.S. Livestock Producers Billions

August 12, 2002

COLUMBUS, Ohio - The impact of heat stress on livestock costs U.S. livestock producers approximately $2.5 billion a year, as much as 50 percent of their net farm income, according to a recent Ohio State University study.

Ohio State University Extension dairy specialist Normand St-Pierre and colleagues analyzed over 250 national journal papers on the nutritional, environmental and physiological impacts of heat stress on livestock in an attempt to quantify the economic impact heat stress has on the commercial animal production industry.

"The results of the study gives producers an opportunity to find more efficient cooling systems for their livestock," said St-Pierre. "Even if every farmer in the United States used the best cooling system for his operation, we'd only be able to decrease that cost by a third. Some of these systems are not very energy efficient." Heat stress, brought about by a combination of temperature, humidity and solar radiation, is one of the leading causes behind livestock health problems, decreased feed intake, negative reproductive impacts and increased mortality, all of which lead to a decrease in production.

Researchers combined the heat stress threshold of 10 animal classes with average minimum and maximum temperature and humidity from 260 weather stations across the country to calculate a temperature humidity index (THI) - a chart where the level of heat stress for all livestock species in every state can be calculated on a daily basis. The animal classes studied included milking cows, heifers, yearlings, beef cows, finishing cattle, sows, feeder hogs, chicken layers, chicken broilers and turkeys.

In addition, researchers incorporated the THI chart with four types of cooling systems (no cooling or strictly shade; fans; a combination of fans and water; and evaporative cooling) to determine the optimal cooling system for each livestock species for every state.

"We found that the best cooling system for dairy cows, in terms of net returns, for most of the United States is one with a combination of fans and a sprinkler system," said St-Pierre. "For other animal classes, like beef cattle, all current cooling systems have costs that exceed their benefits." Ohio is quite representative of the national average when it comes to heat stress. Assuming that all livestock producers were to use the most economically efficient cooling system for their animals, heat stress would cost them a total of $30 million a year.

"That is equal to approximately 1.74 percent of the total national cost of heat stress," said St-Pierre.

The optimal cooling system is the one farmers get the most bang for their buck and is weighed against a variety of factors, including average temperature and humidity for a given month; the number of hours an animal is under heat stress; animal population on a given farm; physical losses (annual losses in production, reproduction and death); and economic losses.

"Evaporative cooling is the best system in terms of cooling down the animals, but is only economically efficient in states with low relative humidity and long periods of high temperatures," St-Pierre said.

Kansas, Oklahoma, Arizona, New Mexico, Nevada and parts of southern California and Texas are examples of such states.

"In other parts of the country, an evaporative cooling system would cost so much money that the cost would exceed the benefits, largely in electrical costs," said St-Pierre. "These systems consume a fair amount of electricity." For example, under the optimum cooling system of fans and sprinklers, electricity consumption would cost Ohio producers more than $2.8 million. Under a commercial evaporative system, that cost would nearly triple.

St-Pierre is working to refine the temperature humidity index chart to include specific heat stress thresholds and the most economic cooling system for livestock producers throughout the United States right down to the county in the state they live in.

"Eventually, I'd like to create a Web site where all the producer has to do is provide his location, what kind of livestock he has, what cooling system he uses or plans to use and the number of animals, and it would calculate his economic cost," said St-Pierre. "It would be more than just a site for information, it'd be a decision-making tool."

Candace Pollock
Normand St-Pierre