Though the early part of the summer was cool, there is the prospect of many hot days ahead. You will need to use all the cooling tools available to protect livestock from heat stress. According to Jay Harmon, agricultural engineer at Iowa State University, the list of heat-related ills for mature livestock is long and complicated, and includes such problems as summer slump, poor reproductive performance and low-feed intake.

He urges you to ensure that you are able to recognize the visible symptoms of heat stress. Elevated respiration rates, abnormal body temperatures, feed avoidance, playing with waterers and crowding into shaded areas as common signs that animals are overheating.

To combat heat stress, Harmon recommends a four-pronged approach that focuses on heat load, evaporative cooling, air speed and body thermal capacity.

First, reduce the animals’ heat load. This includes managing what the animal consumes as well as the heat loads created by the external environmental. Check with your nutritional consultant to get useful hot-weather nutrition tips specific to your herd and location.

One essential strategy to reduce heat load is to provide shade during mid-day and afternoon hours. For confined animals, the western exposure of a building must adequately shade the animals on that side in late afternoon. You may need to place shade cloth or other materials that do not block airflow to block late sunshine, or the animals in that part of the building may have to be relocated.

The second strategy is to use evaporative cooling wisely. While there are several methods, Harmon says water evaporation from wetted skin is one of the more powerful methods available. To be effective, it relies on fairly dry air and high air speed over the animal’s wetted body.

In parts of the Midwest there may be only a few hours during the day when the air is dry enough to use evaporation. Activating fans early in the morning on these days is critical because the air temperature is still less than the animals’ skin temperature, and some cooling can be accomplished.

For example, if the dew point is a constant 71F, and the temperature reaches 93F, the relative humidity at the hottest part of the day will be about 48 percent. On the way to that high temperature, the relative humidity will continue to drop, and once the humidity is below about 65 percent (temperature around 84F), you should turn on evaporative cooling in conjunction with lots of air movement. But the evaporative-cooling water should be turned off in the evening once the temperature drops below 84F. That’s because the relative humidity will again rise past that magic 65 percent.

If you have an instrument to measure hourly relative humidity you will know precisely when to activate the evaporative cooling equipment. Harmon suggests purchasing a pocket model of such an instrument. They’re available for about $60. He advises checking farm and industrial supply catalogs under “thermohygrometers” or “relative humidity instruments.”

The third factor is air velocity. Effectively cooling a pig requires a sustained wind of at least 300 to 500 feet per minute (3.5 to 5.5 miles per hour) over much of the animal’s body. There are several ways to accomplish that, but unless the locale has a dependable wind and a shade tree, mechanical fans are necessary to move the air. Circulation fans throw air effectively about 10 times the distance of the fan’s diameter—you should install fans accordingly.

One frequent problem is that a building will have enough exhaust fans and air inlets to remove heat from a building, but there is inadequate air speed at the animal level to accomplish cooling. Adding water for evaporative cooling will increase the animals’ misery in that situation. He cautions that you must pay attention to air speeds and recommends using a smoke stick or an inexpensive anemometer to help find areas where air speeds aren’t adequate.

The final step is to learn to use an animal’s body thermal capacity. Humans can heat up and cool off fairly quickly compared to a 400 or 800 pound animal. It can take several night-time hours for an overheated sow to get her body temperature down to normal. On days when conditions make it difficult to cool animals in mid-day, it is vital to start cooling the mature animals in the morning, and cool them aggressively with fans in early evening when temperatures moderate.

“Use every opportunity to remove body heat and get the animal back to normal,” says Harmon. For more information on cooling livestock, get a copy of Heating, Cooling and Tempering Air for Livestock Housing, MWPS-34, which can be purchased online at, by calling 800-562-3618, or by sending e-mail to

Jay Harmon, Extension agricultural engineer, Iowa State University