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College of Food, Agricultural, and Environmental Sciences


Take Steps to Protect Livestock from Heat Stress

July 9, 2007

COLUMBUS, Ohio -- As summer progresses and the temperature rises, livestock producers should be mindful of stresses the heat can put on animals.

Maurice Eastridge, an Ohio State University Extension dairy specialist, said that keeping livestock, especially dairy cattle, comfortable under hot conditions is important to maintaining animal health.

"The heat can impact any animal, but dairy cattle are more susceptible because of their high metabolism. Dairy cattle are already generating heat for milk production and additional environmental heat can just make them more stressful," said Eastridge. "Heat stress can impact health, fertility, and milk production, all of which means money lost from a farmer's pocket."

Cattle can exhibit mild heat stress (a combination of temperature and humidity known as the THI index) with temperatures as low as 75 degrees Fahrenheit and a relative humidity of 65 percent. An animal's response to heat stress is to eat less. For each pound of dry matter not consumed, 2 pounds of milk can be lost.

Additionally, heat stress can increase a cow's susceptibility to diseases, specifically mastitis and digestive disorders, and can also create fertility problems -- it is difficult to get heat-stressed cows pregnant or keep them pregnant.

"The miscalculation many farmers make when it comes to heat stress is that they go by the outside ambient temperature to judge whether or not a cow might be suffering from the heat," said Eastridge, who also holds a partial research appointment with the Ohio Agricultural Research and Development Center. "They often forget about the housing area where cattle reside, which is often warmer and more humid than the outside air."

Eastridge said that livestock producers can help minimize heat stress on dairy cattle by following the recommended tips:

• Keep the housing area well ventilated, either by opening the sides for air exchange and/or installing fans.

• Use sprinkler systems to help regulate body temperature. "Place sprinklers over the feeding area to encourage cattle to go to the bunk to eat," said Eastridge. "A combination of sprinklers and fans is the best option for farmers in Ohio. Sprinklers without fans tend to increase the humidity and create additional stresses."

• Keep cattle in holding pens for no more than an hour, as the close proximity of the animals to each other increases heat stress. Make sure holding pens have adequate ventilation, including the use of fans with or without sprinklers.

• Provide an adequate clean water supply -- 1 linear foot for every 20 cows. Keep the water source close to the housing area and provide water to cattle immediately after they exit milking parlors.

• Design a feeding strategy that suits hot conditions. Cut back on wet feed, increase feed with high nutrient, fat, and mineral content, and include high quality forage.

Though dairy cattle are more susceptible to heat stress than other livestock, animals such as beef cattle, pigs, sheep, goats and horses can suffer from heat stress as well.

The following tips can also help keep livestock comfortable and healthy during days of high temperatures:

• Don't overgraze in pastures. Typically, the taller the grass, the cooler the pasture will be.

• Consider feeding more at night rather than in the morning to shift heat fermentation to a cooler part of the day. The heat of digestion can place additional stress on the animal.

• Switch to frequent feedings since high moisture products, like silage, spoils more rapidly in hot weather. This will help control illnesses.

• Work cattle early in the morning to decrease the risk of heat stress.

• Don't over-exercise or transport livestock during the hottest part of the day.

• Sheer rams 60 days prior to breeding to reduce additional stresses when they need to be fertile.

• When cooling down sows, be sure to keep piglets dry. Piglets require the heat.

• Keep finishing pigs as cool as possible.

Signs of heat stress include rapid respiration, laying or standing with mouths open with or without hanging tongues, and excessive salivation.

Information on the THI index can be obtained by logging on to

Candace Pollock
Maurice Eastridge